What does one mole count?

Exactly 6.02214076 × 10^23 representative particles.

What does a peak in an element's mass spectrum represent?

An isotope with a particular mass-to-charge ratio; for singly charged monatomic ions, the position tracks isotopic mass.

What does an empirical formula show?

The lowest whole-number ratio of the elements' atoms in a compound.

How does a mixture differ from a pure substance at the particle level?

A mixture contains chemically distinct representative units in variable proportions; a pure substance contains one element or compound with fixed composition. Different isotopes do not make an elemental sample a mixture.

Which particles make up an atom's nucleus?

Protons and neutrons. Electrons occupy the space outside the nucleus.

What does a larger binding energy on a PES spectrum mean?

More energy is required to remove that electron, so it is held more strongly by the nucleus.

How does atomic radius generally change across a period and down a group?

It decreases from left to right as effective nuclear charge rises, and it increases down a group as additional electron shells increase distance and shielding.

What typical ion charge do Group 1 metals form?

+1, by losing their one valence electron.

How do you convert moles to particles?

Multiply by Avogadro's number: particles = moles × 6.022 × 10^23 mol^-1.

How is average atomic mass estimated from isotope data?

Add each isotopic mass multiplied by its fractional abundance.

How is an element's mass percent in a compound calculated?

Divide the mass contributed by that element by the compound's molar mass, then multiply by 100%.

How can measured elemental composition reveal a sample's purity?

Compare the measured mass fraction with the fraction expected for the pure compound; a mismatch indicates another component.

How do you build a ground-state electron configuration with the Aufbau principle?

For ordinary ground states, move through the periodic table in atomic-number order, filling each s, p, d, or f block as it appears. The subshell capacities are s², p⁶, d¹⁰, and f¹⁴. For example, Br is [Ar] 4s² 3d¹⁰ 4p⁵.

What does the relative area or height of an ideal PES peak indicate?

The relative number of electrons in the corresponding subshell.

How does first ionization energy generally change across a period and down a group?

It increases from left to right as effective nuclear charge rises, and it decreases down a group as distance and shielding make a valence electron easier to remove.

Why do elements in the same group form similar compounds?

Their ground-state valence patterns repeat, including which outer subshells are full or partly full. That leads to similar bonding and typical ion charges.

How do you convert a sample's mass to moles?

Divide its mass by its molar mass: n = m/M.

Which mass-spectrum interpretation lies outside the usual single-element model used in this deck?

Assigning peaks in mixtures or peaks from multiply charged or polyatomic species; the standard model uses singly charged monatomic ions of one element.

What does the law of definite proportions state?

Every pure sample of a given compound has the same element mass ratios.

Why can two samples of the same mixture have different compositions?

Mixture components are physically combined, so their relative amounts are not fixed by a chemical formula.

How does Coulomb's law connect charge and separation to attraction?

Attraction grows with the magnitude of the charge product and decreases with the square of the separation distance.

Which PES electrons usually appear at the highest binding energy?

Core electrons closest to the nucleus, because they feel the strongest nuclear attraction.

How does electron affinity generally change across a period and down a group?

Electron gain generally becomes more favorable from left to right across a period and less favorable down a group as distance and shielding increase. Stable subshell patterns create substantial exceptions.

Why are alkali metals generally more reactive down the group?

Their valence electron is farther from the nucleus and easier to remove.

How many moles are in 18.0 g of H₂O?

About 0.999 mol. Use 18.0 g ÷ 18.02 g mol^-1.

An element is 75% isotope 10 and 25% isotope 11; what is its average atomic mass?

10.25 u. Calculate (0.75 × 10) + (0.25 × 11).

A compound is 40.0% C, 6.7% H, and 53.3% O by mass; what is its empirical formula?

CH₂O. For a 100 g sample, convert each mass to moles and divide by the smallest amount.

A 10.0 g impure sample contains 8.5 g of the target compound; what is its mass-percent purity?

85%. Calculate (8.5 g ÷ 10.0 g) × 100%.

Which electrons are removed first when a transition metal forms a cation?

Electrons in the occupied orbital with the highest principal quantum number: 4s before 3d. For example, Fe²⁺ is [Ar] 3d⁶.

A PES spectrum has peaks proportional to 2, 2, and 6 electrons; which configuration fits?

1s² 2s² 2p⁶, the configuration of Ne.

How does electronegativity generally change across a period and down a group?

It increases from left to right across a period and decreases down a group as atomic size and shielding increase.

What empirical formula results from Al³⁺ and O²⁻?

Al₂O₃, because two Al³⁺ ions balance three O²⁻ ions.

How does a particle's mass in atomic mass units relate to its molar mass?

The numerical value is the same: a molecular or formula-unit mass of x u corresponds to a molar mass of x g mol^-1.

What does the tallest isotope peak usually indicate in a simple mass spectrum?

The most abundant isotope, assuming comparable detection response and singly charged ions.

How much oxygen is present in 25.0 g of a compound that is 32.0% oxygen by mass?

8.00 g O. Multiply 25.0 g by 0.320.

What does a particle diagram with two unbonded species in changing ratios represent?

A mixture, because more than one particle type is present and the ratio is not fixed in a formula unit.

What distinguishes valence electrons from core electrons?

Valence electrons are available for bonding or ion formation; main-group valence electrons occupy the outermost shell, while transition metals may also use (n−1)d electrons. Core electrons mainly shield nuclear charge.

Why can PES peak groups reveal an atom's occupied subshells?

Electrons in different subshells require distinct removal energies, producing separate binding-energy groups.

How do ion radii compare with neutral atoms and within an isoelectronic series?

Cations are smaller than their neutral atoms, while anions are larger. Among species with the same electron count, more protons pull the electrons closer and produce the smaller radius.

What formula is expected for a compound between a Group 2 metal M and a Group 17 nonmetal X?

MX₂, because M forms M²⁺ and X forms X⁻.

When is a covalent bond considered nonpolar?

When the bonded atoms have identical or very similar electronegativities, so the shared electron density is distributed approximately evenly.

Why does a bonded pair of atoms have an equilibrium bond length?

At that separation, attractive and repulsive interactions balance at minimum potential energy.

How are particles arranged in an ionic solid?

Cations and anions occupy a repeating three-dimensional lattice held by electrostatic attraction.

What model explains bonding in a metal?

Positive metal cores are held together by attraction to mobile, delocalized valence electrons.

How do you construct a Lewis diagram?

Count total valence electrons, adding electrons for a negative charge and subtracting them for a positive charge. Choose a skeleton, connect atoms with single bonds, complete terminal duets or octets, and place remaining electrons on the central atom. Add multiple bonds if needed, then check the electron total and formal charges.

What does resonance mean in a molecule or ion?

Resonance uses two or more valid Lewis diagrams with the same atom arrangement but different electron placement. The actual electron distribution is a hybrid; equivalent contributors have equal weight.

What determines molecular shape in VSEPR theory?

Electron domains around the central atom arrange to minimize repulsions.

How does an ionic bond differ from a covalent bond?

Ionic bonding is attraction among oppositely charged ions in an extended structure; covalent bonding uses shared electron density between atoms.

What happens to potential energy when bonded atoms are pushed much closer than equilibrium?

Potential energy rises sharply because nucleus–nucleus and electron–electron repulsions dominate.

Why are many ionic solids brittle?

A shifted lattice can align like charges, creating strong repulsion that splits the crystal.

What molecular shapes arise from two electron domains with no lone pairs and from three domains with zero or one lone pair?

Two bonding domains give linear with a 180° angle. Three domains with no lone pairs give trigonal planar with 120° angles; replacing one bond with a lone pair gives bent with an angle slightly below 120°.

Advanced High School Chemistry Flashcards: Complete 9-Part Course Review

Review a rigorous nine-part high school chemistry course with 450 concise cards covering concepts, models, equations, calculation setup, and lab reasoning.

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Об этой колоде

Study advanced high school chemistry through 450 independently written English flashcards arranged as one nine-part sequence. The course moves from atomic structure and bonding to properties of substances and mixtures, reactions, kinetics, thermochemistry, equilibrium, acids and bases, thermodynamics, and electrochemistry. Prerequisites appear before dependent models and calculations.

What the cards practice

The cards practice five useful recall paths: concept to explanation; model or representation to interpretation; equation to meaning and use; short setup to a result with units and reasoning; and laboratory observation to a chemical conclusion. This includes definitions, relationships, conditions, contrasts, particle and energy models, focused calculation steps, measurements, errors, and visible changes.

Selected reverse and contrast prompts appear only when the reverse direction has one clear standalone target. Mechanical permutations, graph-dependent prompts that need a missing figure, copied test formats, long multipart derivations, and visual recall tied to third-party figures are excluded. The review scheduler handles long-term spacing after installation.

The prompts, answers, examples, organization, metadata, and cover were created independently from common chemistry knowledge and original work. No protected questions, answer choices, scoring materials, curriculum prose, commercial card text, source figures, or third-party media were copied.

The Common knowledge · CC0 1.0 label applies only to the original prompts, answers, examples, organization, metadata, and cover, to the extent applicable rights exist. It does not claim ownership of scientific facts, equations, or third-party material.

Карточки в этой колоде

Карточка 1
Вопрос
What does one mole count?
Ответ
Exactly 6.02214076 × 10^23 representative particles.
Карточка 2
Вопрос
What does a peak in an element's mass spectrum represent?
Ответ
An isotope with a particular mass-to-charge ratio; for singly charged monatomic ions, the position tracks isotopic mass.
Карточка 3
Вопрос
What does an empirical formula show?
Ответ
The lowest whole-number ratio of the elements' atoms in a compound.
Карточка 4
Вопрос
How does a mixture differ from a pure substance at the particle level?
Ответ
A mixture contains chemically distinct representative units in variable proportions; a pure substance contains one element or compound with fixed composition. Different isotopes do not make an elemental sample a mixture.
Карточка 5
Вопрос
Which particles make up an atom's nucleus?
Ответ
Protons and neutrons. Electrons occupy the space outside the nucleus.
Карточка 6
Вопрос
What does a larger binding energy on a PES spectrum mean?
Ответ
More energy is required to remove that electron, so it is held more strongly by the nucleus.
Карточка 7
Вопрос
How does atomic radius generally change across a period and down a group?
Ответ
It decreases from left to right as effective nuclear charge rises, and it increases down a group as additional electron shells increase distance and shielding.
Карточка 8
Вопрос
What typical ion charge do Group 1 metals form?
Ответ
+1, by losing their one valence electron.
Карточка 9
Вопрос
How do you convert moles to particles?
Ответ
Multiply by Avogadro's number: particles = moles × 6.022 × 10^23 mol^-1.
Карточка 10
Вопрос
How is average atomic mass estimated from isotope data?
Ответ
Add each isotopic mass multiplied by its fractional abundance.
Карточка 11
Вопрос
How is an element's mass percent in a compound calculated?
Ответ
Divide the mass contributed by that element by the compound's molar mass, then multiply by 100%.
Карточка 12
Вопрос
How can measured elemental composition reveal a sample's purity?
Ответ
Compare the measured mass fraction with the fraction expected for the pure compound; a mismatch indicates another component.
Карточка 13
Вопрос
How do you build a ground-state electron configuration with the Aufbau principle?
Ответ
For ordinary ground states, move through the periodic table in atomic-number order, filling each s, p, d, or f block as it appears. The subshell capacities are s², p⁶, d¹⁰, and f¹⁴. For example, Br is [Ar] 4s² 3d¹⁰ 4p⁵.
Карточка 14
Вопрос
What does the relative area or height of an ideal PES peak indicate?
Ответ
The relative number of electrons in the corresponding subshell.
Карточка 15
Вопрос
How does first ionization energy generally change across a period and down a group?
Ответ
It increases from left to right as effective nuclear charge rises, and it decreases down a group as distance and shielding make a valence electron easier to remove.
Карточка 16
Вопрос
Why do elements in the same group form similar compounds?
Ответ
Their ground-state valence patterns repeat, including which outer subshells are full or partly full. That leads to similar bonding and typical ion charges.
Карточка 17
Вопрос
How do you convert a sample's mass to moles?
Ответ
Divide its mass by its molar mass: n = m/M.
Карточка 18
Вопрос
Which mass-spectrum interpretation lies outside the usual single-element model used in this deck?
Ответ
Assigning peaks in mixtures or peaks from multiply charged or polyatomic species; the standard model uses singly charged monatomic ions of one element.
Карточка 19
Вопрос
What does the law of definite proportions state?
Ответ
Every pure sample of a given compound has the same element mass ratios.
Карточка 20
Вопрос
Why can two samples of the same mixture have different compositions?
Ответ
Mixture components are physically combined, so their relative amounts are not fixed by a chemical formula.
Карточка 21
Вопрос
How does Coulomb's law connect charge and separation to attraction?
Ответ
Attraction grows with the magnitude of the charge product and decreases with the square of the separation distance.
Карточка 22
Вопрос
Which PES electrons usually appear at the highest binding energy?
Ответ
Core electrons closest to the nucleus, because they feel the strongest nuclear attraction.
Карточка 23
Вопрос
How does electron affinity generally change across a period and down a group?
Ответ
Electron gain generally becomes more favorable from left to right across a period and less favorable down a group as distance and shielding increase. Stable subshell patterns create substantial exceptions.
Карточка 24
Вопрос
Why are alkali metals generally more reactive down the group?
Ответ
Their valence electron is farther from the nucleus and easier to remove.
Карточка 25
Вопрос
How many moles are in 18.0 g of H₂O?
Ответ
About 0.999 mol. Use 18.0 g ÷ 18.02 g mol^-1.
Карточка 26
Вопрос
An element is 75% isotope 10 and 25% isotope 11; what is its average atomic mass?
Ответ
10.25 u. Calculate (0.75 × 10) + (0.25 × 11).
Карточка 27
Вопрос
A compound is 40.0% C, 6.7% H, and 53.3% O by mass; what is its empirical formula?
Ответ
CH₂O. For a 100 g sample, convert each mass to moles and divide by the smallest amount.
Карточка 28
Вопрос
A 10.0 g impure sample contains 8.5 g of the target compound; what is its mass-percent purity?
Ответ
85%. Calculate (8.5 g ÷ 10.0 g) × 100%.
Карточка 29
Вопрос
Which electrons are removed first when a transition metal forms a cation?
Ответ
Electrons in the occupied orbital with the highest principal quantum number: 4s before 3d. For example, Fe²⁺ is [Ar] 3d⁶.
Карточка 30
Вопрос
A PES spectrum has peaks proportional to 2, 2, and 6 electrons; which configuration fits?
Ответ
1s² 2s² 2p⁶, the configuration of Ne.
Карточка 31
Вопрос
How does electronegativity generally change across a period and down a group?
Ответ
It increases from left to right across a period and decreases down a group as atomic size and shielding increase.
Карточка 32
Вопрос
What empirical formula results from Al³⁺ and O²⁻?
Ответ
Al₂O₃, because two Al³⁺ ions balance three O²⁻ ions.
Карточка 33
Вопрос
How does a particle's mass in atomic mass units relate to its molar mass?
Ответ
The numerical value is the same: a molecular or formula-unit mass of x u corresponds to a molar mass of x g mol^-1.
Карточка 34
Вопрос
What does the tallest isotope peak usually indicate in a simple mass spectrum?
Ответ
The most abundant isotope, assuming comparable detection response and singly charged ions.
Карточка 35
Вопрос
How much oxygen is present in 25.0 g of a compound that is 32.0% oxygen by mass?
Ответ
8.00 g O. Multiply 25.0 g by 0.320.
Карточка 36
Вопрос
What does a particle diagram with two unbonded species in changing ratios represent?
Ответ
A mixture, because more than one particle type is present and the ratio is not fixed in a formula unit.
Карточка 37
Вопрос
What distinguishes valence electrons from core electrons?
Ответ
Valence electrons are available for bonding or ion formation; main-group valence electrons occupy the outermost shell, while transition metals may also use (n−1)d electrons. Core electrons mainly shield nuclear charge.
Карточка 38
Вопрос
Why can PES peak groups reveal an atom's occupied subshells?
Ответ
Electrons in different subshells require distinct removal energies, producing separate binding-energy groups.
Карточка 39
Вопрос
How do ion radii compare with neutral atoms and within an isoelectronic series?
Ответ
Cations are smaller than their neutral atoms, while anions are larger. Among species with the same electron count, more protons pull the electrons closer and produce the smaller radius.
Карточка 40
Вопрос
What formula is expected for a compound between a Group 2 metal M and a Group 17 nonmetal X?
Ответ
MX₂, because M forms M²⁺ and X forms X⁻.
Карточка 41
Вопрос
When is a covalent bond considered nonpolar?
Ответ
When the bonded atoms have identical or very similar electronegativities, so the shared electron density is distributed approximately evenly.
Карточка 42
Вопрос
Why does a bonded pair of atoms have an equilibrium bond length?
Ответ
At that separation, attractive and repulsive interactions balance at minimum potential energy.
Карточка 43
Вопрос
How are particles arranged in an ionic solid?
Ответ
Cations and anions occupy a repeating three-dimensional lattice held by electrostatic attraction.
Карточка 44
Вопрос
What model explains bonding in a metal?
Ответ
Positive metal cores are held together by attraction to mobile, delocalized valence electrons.
Карточка 45
Вопрос
How do you construct a Lewis diagram?
Ответ
Count total valence electrons, adding electrons for a negative charge and subtracting them for a positive charge. Choose a skeleton, connect atoms with single bonds, complete terminal duets or octets, and place remaining electrons on the central atom. Add multiple bonds if needed, then check the electron total and formal charges.
Карточка 46
Вопрос
What does resonance mean in a molecule or ion?
Ответ
Resonance uses two or more valid Lewis diagrams with the same atom arrangement but different electron placement. The actual electron distribution is a hybrid; equivalent contributors have equal weight.
Карточка 47
Вопрос
What determines molecular shape in VSEPR theory?
Ответ
Electron domains around the central atom arrange to minimize repulsions.
Карточка 48
Вопрос
How does an ionic bond differ from a covalent bond?
Ответ
Ionic bonding is attraction among oppositely charged ions in an extended structure; covalent bonding uses shared electron density between atoms.
Карточка 49
Вопрос
What happens to potential energy when bonded atoms are pushed much closer than equilibrium?
Ответ
Potential energy rises sharply because nucleus–nucleus and electron–electron repulsions dominate.
Карточка 50
Вопрос
Why are many ionic solids brittle?
Ответ
A shifted lattice can align like charges, creating strong repulsion that splits the crystal.
Карточка 51
Вопрос
What molecular shapes arise from two electron domains with no lone pairs and from three domains with zero or one lone pair?
Ответ
Two bonding domains give linear with a 180° angle. Three domains with no lone pairs give trigonal planar with 120° angles; replacing one bond with a lone pair gives bent with an angle slightly below 120°.
Карточка 52
Вопрос
Why are metals electrically conductive as solids?
Ответ
Their delocalized electrons can move through the solid when an electric field is applied.
Карточка 53
Вопрос
How is formal charge calculated for an atom in a Lewis diagram?
Ответ
Formal charge = valence electrons − nonbonding electrons − half the bonding electrons.
Карточка 54
Вопрос
Why can't electronegativity difference alone classify a bond as ionic or covalent?
Ответ
Bonding lies on a continuum. A larger difference means more ionic character, but the element types and especially the compound's properties give the best classification.
Карточка 55
Вопрос
Which shapes and bond-angle trends arise as lone pairs replace bonds in four electron domains?
Ответ
Four bonds give tetrahedral with ideal 109.5° angles. One lone pair gives trigonal pyramidal with smaller angles; two lone pairs give bent with typically smaller angles again because lone pairs repel more strongly than bonding pairs.
Карточка 56
Вопрос
What feature of a potential-energy curve represents bond dissociation energy?
Ответ
The energy difference from the curve's minimum to the separated-atoms limit.
Карточка 57
Вопрос
When does an ionic compound conduct electricity?
Ответ
When molten or dissolved so its ions can move; not as a rigid solid lattice.
Карточка 58
Вопрос
What is a substitutional alloy?
Ответ
An alloy in which atoms of a similar size replace some host-metal atoms in the lattice.
Карточка 59
Вопрос
How do two, three, and four electron domains map to hybridization?
Ответ
Two domains map to sp, three to sp², and four to sp³, with ideal angles of 180°, 120°, and 109.5°. Hybridization involving d orbitals is outside this deck’s scope.
Карточка 60
Вопрос
What usually makes one resonance contributor more favorable than another?
Ответ
Smaller formal-charge magnitudes, appropriate negative charge on more electronegative atoms, and complete valence shells where applicable.
Карточка 61
Вопрос
How many sigma and pi bonds are in single, double, and triple bonds?
Ответ
A single bond has one sigma bond; a double has one sigma and one pi bond; a triple has one sigma and two pi bonds. Head-on sigma overlap is stronger than side-by-side pi overlap.
Карточка 62
Вопрос
Why is a polar covalent bond polar?
Ответ
Unequal electronegativity creates an uneven sharing of electron density and partial charges.
Карточка 63
Вопрос
Which molecular shapes arise as lone pairs replace bonds in five electron domains?
Ответ
Five bonds give trigonal bipyramidal; four bonds and one lone pair give seesaw; three bonds and two lone pairs give T-shaped; two bonds and three lone pairs give linear.
Карточка 64
Вопрос
How do ionic charge and ionic radius affect attraction between ions?
Ответ
Larger charge magnitudes and smaller ionic radii produce stronger attraction because the charge product increases and the ion centers are closer.
Карточка 65
Вопрос
Why do ionic solids often have high melting points?
Ответ
Many strong Coulombic attractions throughout the lattice must be overcome to free the ions.
Карточка 66
Вопрос
What is an interstitial alloy?
Ответ
A smaller atom occupies holes between host-metal atoms, often making lattice layers harder to slide.
Карточка 67
Вопрос
What shape has six bonding domains and no lone pairs on the central atom?
Ответ
Octahedral.
Карточка 68
Вопрос
Which elements commonly form incomplete octets in stable Lewis diagrams?
Ответ
Hydrogen forms a duet, and electron-deficient central atoms such as boron or beryllium can have fewer than eight electrons.
Карточка 69
Вопрос
How do bond order and atomic size affect covalent bond length and strength?
Ответ
Within a comparable bond family, higher bond order gives shorter, stronger bonds. Larger bonded atoms generally give longer bonds, which are often weaker because their orbitals overlap less effectively.
Карточка 70
Вопрос
What bonding model best fits a sample that is malleable and conducts as a solid?
Ответ
Metallic bonding with mobile, delocalized electrons and nondirectional attractions.
Карточка 71
Вопрос
What shape has six electron domains, five bonds, and one lone pair?
Ответ
Square pyramidal.
Карточка 72
Вопрос
Which lattice should have stronger attractions: MgO or NaCl, assuming similar separations?
Ответ
MgO, because the charge product for Mg²⁺ and O²⁻ is larger than for Na⁺ and Cl⁻.
Карточка 73
Вопрос
Why are pure metals often malleable?
Ответ
Metal cores can shift while the mobile electron sea maintains nondirectional attraction instead of exposing fixed like-charge planes.
Карточка 74
Вопрос
What is the best Lewis structure for CO₂?
Ответ
O=C=O, with two lone pairs on each oxygen and no formal charges.
Карточка 75
Вопрос
What shape has six electron domains, four bonds, and two opposite lone pairs?
Ответ
Square planar.
Карточка 76
Вопрос
What limitation does an odd total number of valence electrons create for a Lewis diagram?
Ответ
At least one electron must remain unpaired, so not every atom can have a complete paired-electron octet.
Карточка 77
Вопрос
What does a higher bond order do to a bond's potential-energy curve?
Ответ
It generally places the minimum at a shorter internuclear distance and makes the well deeper, corresponding to a shorter bond and a larger bond-dissociation energy.
Карточка 78
Вопрос
When can a carbon–carbon double bond produce geometric isomers?
Ответ
When each carbon has two different substituents. The pi bond restricts rotation, so distinct spatial arrangements can persist.
Карточка 79
Вопрос
When may a third-period central atom exceed an octet in a Lewis diagram?
Ответ
When the valid electron count and lower formal charges favor an expanded valence shell, as in species such as SF₆.
Карточка 80
Вопрос
How do you decide whether a molecule with polar bonds is polar overall?
Ответ
Add the bond-dipole vectors using the molecular shape; symmetry may cancel them, while an asymmetric arrangement leaves a net dipole.
Карточка 81
Вопрос
Which interparticle forces act between all atoms and molecules?
Ответ
London dispersion forces, caused by temporary and induced dipoles.
Карточка 82
Вопрос
What four broad solid types does this deck compare?
Ответ
Ionic, metallic, molecular, and covalent-network solids.
Карточка 83
Вопрос
How do gas particles differ from liquid particles?
Ответ
Gas particles are much farther apart and move independently; liquid particles stay close but can move past one another.
Карточка 84
Вопрос
What relationship connects pressure, volume, amount, and temperature for an ideal gas?
Ответ
PV = nRT, with absolute temperature in kelvins and units consistent with R.
Карточка 85
Вопрос
What does temperature measure in kinetic molecular theory?
Ответ
The particles' average translational kinetic energy.
Карточка 86
Вопрос
What two ideal-gas assumptions fail most clearly for real gases?
Ответ
Particles have nonzero volume and experience intermolecular attractions.
Карточка 87
Вопрос
How is molarity defined?
Ответ
Moles of solute per liter of solution: M = n/V.
Карточка 88
Вопрос
What must a correct particulate diagram of NaCl(aq) show?
Ответ
Separated Na⁺ and Cl⁻ ions in a 1:1 ratio, each surrounded by oriented water molecules.
Карточка 89
Вопрос
Which separation method removes an insoluble solid from a liquid?
Ответ
Filtration: the solid stays as residue while the liquid passes as filtrate.
Карточка 90
Вопрос
What does “like dissolves like” mean at the particle level?
Ответ
A solute tends to dissolve when new solute–solvent attractions can compete with the attractions disrupted in the pure substances.
Карточка 91
Вопрос
What happens when matter absorbs electromagnetic radiation?
Ответ
Its particles move to an allowed higher-energy state when the photon energy matches the energy gap.
Карточка 92
Вопрос
Which equations connect photon energy, frequency, and wavelength?
Ответ
E = hν and c = λν.
Карточка 93
Вопрос
What is the Beer–Lambert law?
Ответ
A = εbc: absorbance equals molar absorptivity at the chosen wavelength times path length times concentration.
Карточка 94
Вопрос
What molecular features generally strengthen London dispersion forces?
Ответ
More electrons and a more polarizable cloud strengthen temporary dipoles; greater contact area and accessible π-electron density can also strengthen the attraction.
Карточка 95
Вопрос
Why do molecular solids usually have low melting points and fail to conduct electricity?
Ответ
Distinct molecules are held together by relatively weak intermolecular forces, while their valence electrons stay localized in bonds and lone pairs.
Карточка 96
Вопрос
How do particles move in a solid?
Ответ
They vibrate about fixed positions and do not translate past one another.
Карточка 97
Вопрос
What graph shapes connect V or P with T(K) or n for an ideal gas?
Ответ
All four are straight lines through the origin: V versus T(K) at fixed n and P; P versus T(K) at fixed n and V; V versus n at fixed P and T; and P versus n at fixed V and T.
Карточка 98
Вопрос
At the same temperature, which gas has the greater average molecular speed: He or Xe?
Ответ
He. Both have the same average kinetic energy, but KE = ½mv² means the lower-mass particles move faster.
Карточка 99
Вопрос
Why do real gases deviate more at high pressure?
Ответ
Particles are crowded, so their own volume is no longer negligible compared with the container volume.
Карточка 100
Вопрос
Which relationship describes dilution when solute amount is conserved?
Ответ
M₁V₁ = M₂V₂.
Карточка 101
Вопрос
Why does an aqueous ionic solution conduct electricity?
Ответ
Dissolved ions are mobile and carry charge through the solution.
Карточка 102
Вопрос
Which property lets simple distillation separate two liquids?
Ответ
A sufficient difference in volatility or boiling point, so the vapor is enriched in the more volatile component.
Карточка 103
Вопрос
Why are many ionic compounds soluble in water but poorly soluble in a nonpolar solvent?
Ответ
Water can form strong ion–dipole attractions that stabilize separated ions; a nonpolar solvent cannot provide comparable attractions.
Карточка 104
Вопрос
Which molecular transition is commonly associated with microwave absorption?
Ответ
A transition between quantized rotational energy levels.
Карточка 105
Вопрос
What frequency corresponds to a 600. nm photon?
Ответ
5.00 × 10^14 s^-1. Use ν = c/λ with 600. nm = 6.00 × 10^-7 m.
Карточка 106
Вопрос
What is the absorbance to two significant figures when ε = 2.0 × 10² L mol^-1 cm^-1, b = 1.00 cm, and c = 0.0020 M?
Ответ
0.40. Use A = εbc.
Карточка 107
Вопрос
What conditions allow hydrogen bonding between two molecules?
Ответ
One molecule must donate an H covalently bonded to N, O, or F, and the other must provide a lone pair on N, O, or F. A molecule can be a donor, an acceptor, or both.
Карточка 108
Вопрос
Why are covalent-network solids often very hard with high melting points?
Ответ
A continuous network of strong covalent bonds must be disrupted to deform or melt the solid.
Карточка 109
Вопрос
Why do a substance's solid and liquid phases usually have similar molar volumes?
Ответ
Their particles remain in close contact in both phases, even though liquid particles can move past one another.
Карточка 110
Вопрос
How is a gas mixture's total pressure related to its component pressures?
Ответ
Ptotal = ΣPi; each partial pressure is the pressure that component would exert alone in the same volume and temperature.
Карточка 111
Вопрос
What microscopic events create gas pressure?
Ответ
Gas particles collide with container walls and transfer momentum.
Карточка 112
Вопрос
Why do intermolecular attractions matter more for gases at low temperature?
Ответ
Particles move more slowly, so attractions can alter their paths and promote condensation.
Карточка 113
Вопрос
What is the final concentration after 50.0 mL of 2.00 M solution is diluted to 200.0 mL?
Ответ
0.500 M. Use M₂ = M₁V₁/V₂.
Карточка 114
Вопрос
What must a particulate representation of a solution communicate?
Ответ
The relative concentrations of its components and the particle-level interactions among those components.
Карточка 115
Вопрос
What causes components to separate in chromatography?
Ответ
They differ in attraction to the stationary phase and the mobile phase, so they travel at different rates.
Карточка 116
Вопрос
Why are many polar molecular solutes soluble in water?
Ответ
Dipole attractions or hydrogen bonds with water can replace the solute–solute and water–water attractions disrupted during mixing.
Карточка 117
Вопрос
Why does an atom produce discrete spectral lines?
Ответ
Its electrons can occupy only quantized energy levels, so only photons matching allowed energy differences are absorbed or emitted.
Карточка 118
Вопрос
How does photon energy change when frequency doubles?
Ответ
It doubles because E = hν.
Карточка 119
Вопрос
Why is a calibration curve useful in spectrophotometry?
Ответ
It relates measured absorbance to known concentrations, letting an unknown concentration be read by interpolation within the linear range.
Карточка 120
Вопрос
How does an ion–dipole attraction form, and how does it compare with dipole–dipole attraction?
Ответ
An ion attracts the oppositely charged end of a polar molecule. Ion–dipole attractions tend to be stronger than dipole–dipole attractions.
Карточка 121
Вопрос
Which solid type is usually both conductive and malleable?
Ответ
A metallic solid, because its delocalized electrons move and its nondirectional bonding tolerates layer shifts.
Карточка 122
Вопрос
How does a crystalline solid differ from an amorphous solid?
Ответ
A crystalline solid has long-range repeating order; an amorphous solid lacks that long-range periodic arrangement.
Карточка 123
Вопрос
How is a gas component's partial pressure found from mole fraction?
Ответ
Pi = XiPtotal.
Карточка 124
Вопрос
How does heating a fixed-volume gas affect its pressure in the ideal model?
Ответ
Pressure rises because faster particles collide with the walls more forcefully and frequently.
Карточка 125
Вопрос
Why can attractions make a real gas's measured pressure lower than the ideal prediction?
Ответ
Attractions pull approaching particles away from the walls, reducing momentum transfer during wall collisions.
Карточка 126
Вопрос
How many moles of ions result from complete dissolution of 0.20 mol CaCl₂?
Ответ
0.60 mol ions: 0.20 mol Ca²⁺ plus 0.40 mol Cl⁻.
Карточка 127
Вопрос
How should water orient around Cl⁻ in a particle model?
Ответ
Its partially positive hydrogen ends point toward Cl⁻.
Карточка 128
Вопрос
Can filtration separate dissolved components of a liquid solution?
Ответ
No. Dissolved particles pass through the filter with the solvent; filtration only retains an insoluble solid.
Карточка 129
Вопрос
Why do nonpolar molecular solutes often dissolve in nonpolar solvents?
Ответ
Both rely mainly on compatible London dispersion forces, so mixing can replace the attractions disrupted in the separate substances.
Карточка 130
Вопрос
What does a shorter absorbed wavelength imply about an energy transition?
Ответ
A larger energy gap because E = hc/λ.
Карточка 131
Вопрос
What is the energy of a photon with frequency 5.0 × 10^14 s^-1?
Ответ
3.3 × 10^-19 J. Multiply by Planck's constant: E = (6.626 × 10^-34 J·s)(5.0 × 10^14 s^-1).
Карточка 132
Вопрос
How does doubling cuvette path length affect absorbance in the linear Beer–Lambert range?
Ответ
Absorbance doubles if concentration and molar absorptivity stay constant.
Карточка 133
Вопрос
How can noncovalent interactions affect a large biomolecule?
Ответ
Attractions between molecules or between different regions of the same molecule help set its shape, which strongly affects its properties and function.
Карточка 134
Вопрос
Why does an ionic solid usually fail to conduct as a solid?
Ответ
Its ions are fixed in lattice positions. The same substance conducts when molten or dissolved because the ions can then move.
Карточка 135
Вопрос
Why does a gas have no definite shape or volume?
Ответ
Its widely spaced particles move constantly and experience minimal interparticle attraction, so they spread through the available container.
Карточка 136
Вопрос
What graph shapes show the inverse pressure–volume relationship for a fixed amount of ideal gas at constant temperature?
Ответ
A plot of P against V is a decreasing curve, while P against 1/V is a straight line through the origin.
Карточка 137
Вопрос
At the same temperature, do different ideal gases have different average kinetic energies?
Ответ
No. Average translational kinetic energy depends only on absolute temperature.
Карточка 138
Вопрос
Under which conditions is ideal-gas behavior most accurate?
Ответ
Low pressure and high temperature, where particles are far apart and attractions matter least.
Карточка 139
Вопрос
What particle-level feature distinguishes a solution from a heterogeneous mixture?
Ответ
A solution—whether solid, liquid, or gas—is uniform throughout; a heterogeneous mixture has regions or phases with different compositions.
Карточка 140
Вопрос
How should water orient around Na⁺ in a particulate model?
Ответ
Its partially negative oxygen end points toward Na⁺.
Карточка 141
Вопрос
In paper chromatography, why does one solute spot travel farther than another?
Ответ
It interacts more strongly with the mobile phase or more weakly with the stationary phase. With known phase polarities, that travel difference can reveal relative solute polarity.
Карточка 142
Вопрос
What energy competition helps explain whether an ionic solid dissolves?
Ответ
The energy needed to separate lattice ions competes with the energy released when ion–solvent attractions form.
Карточка 143
Вопрос
Which molecular motions commonly absorb infrared radiation?
Ответ
Bond vibrations whose changing dipole can interact with the radiation.
Карточка 144
Вопрос
Why must wavelength be converted to meters in c = λν when c is in m s^-1?
Ответ
Consistent units are required so meters cancel correctly and frequency comes out in s^-1.
Карточка 145
Вопрос
How can fingerprints on a cuvette affect a visible-light absorbance reading?
Ответ
They can absorb or scatter extra light, making measured absorbance too high and the inferred concentration too high.
Карточка 146
Вопрос
What causes and controls the strength of dipole–dipole attractions?
Ответ
Opposite partial charges on neighboring polar molecules attract. Strength increases with larger molecular dipoles and depends on how favorably the dipoles are oriented.
Карточка 147
Вопрос
Why is graphite conductive and soft while diamond is insulating and hard?
Ответ
Graphite has delocalized electrons within its sheets, so it conducts, and its layers can slide, so it is soft. Diamond has a rigid three-dimensional network of localized covalent bonds, making it hard and insulating.
Карточка 148
Вопрос
Why are gases much more compressible than liquids?
Ответ
Gas particles have large empty spaces between them; liquid particles are already close together.
Карточка 149
Вопрос
What volume does 0.500 mol CO₂ occupy at 1.00 atm and 300. K if it behaves ideally?
Ответ
12.3 L. Use V = nRT/P = (0.500 mol)(0.08206 L atm mol^-1 K^-1)(300. K)/(1.00 atm).
Карточка 150
Вопрос
Why does a lighter gas effuse faster than a heavier gas at the same temperature?
Ответ
Its particles have a higher average speed because equal average kinetic energy is shared by less mass.
Карточка 151
Вопрос
How does finite particle volume affect a real gas at very high pressure?
Ответ
The free volume available for particle motion is smaller than the container volume assumed by the ideal model.
Карточка 152
Вопрос
How should 250.0 mL of 0.100 M NaCl be prepared from solid NaCl?
Ответ
Dissolve 0.0250 mol NaCl, or 1.46 g, then dilute to exactly 250.0 mL in a volumetric flask.
Карточка 153
Вопрос
What changes in a particle diagram when a solution is diluted without losing solute?
Ответ
The solute-particle count stays constant while solvent volume and particle spacing increase.
Карточка 154
Вопрос
Why is fractional distillation better than simple distillation for liquids with close boiling points?
Ответ
Repeated vaporization–condensation steps enrich the vapor in the more volatile component more effectively.
Карточка 155
Вопрос
Why are oil and water usually immiscible?
Ответ
Water's strong hydrogen-bond network isn't replaced by equally strong water–oil attractions, so the substances separate into phases.
Карточка 156
Вопрос
Which molecular transition is commonly associated with ultraviolet or visible absorption?
Ответ
A transition between electronic energy levels.
Карточка 157
Вопрос
Which photon carries more energy, blue light or red light?
Ответ
Blue light, because it has shorter wavelength and higher frequency.
Карточка 158
Вопрос
Why is absorbance often measured at the wavelength of maximum absorbance in Beer–Lambert analysis?
Ответ
It gives the largest concentration-sensitive signal, and the flat top near the maximum makes small wavelength-setting errors less influential.
Карточка 159
Вопрос
What creates a dipole–induced-dipole attraction, and what controls its strength?
Ответ
A permanent dipole distorts a nearby nonpolar particle's electron cloud and creates an attractive temporary dipole. A larger permanent dipole and a more polarizable nonpolar partner make the attraction stronger.
Карточка 160
Вопрос
How do stronger intermolecular forces affect vapor pressure, boiling point, and melting point?
Ответ
They lower vapor pressure and raise boiling point. Melting point often rises too, but the trend is less direct because melting rearranges rather than fully separates particles.
Карточка 161
Вопрос
How do particles behave in a liquid?
Ответ
They stay in close contact while moving and colliding continuously. Temperature and interparticle attractions affect their arrangement and motion.
Карточка 162
Вопрос
Why must Celsius temperature be converted to kelvins in gas-law calculations?
Ответ
Gas-law proportionalities require an absolute temperature scale whose zero corresponds to zero extrapolated thermal motion.
Карточка 163
Вопрос
How does raising temperature change a Maxwell–Boltzmann speed distribution?
Ответ
The distribution broadens, its peak lowers and shifts right, and a larger fraction of particles have high speed.
Карточка 164
Вопрос
Why does the ideal-gas model treat collisions as elastic?
Ответ
It assumes total kinetic energy is conserved in particle–particle and particle–wall collisions.
Карточка 165
Вопрос
How many moles of solute are in 75.0 mL of a 0.400 M solution?
Ответ
0.0300 mol. Multiply 0.400 mol L^-1 by 0.0750 L.
Карточка 166
Вопрос
For equal solution volumes drawn at the same scale, what shows which solution is more concentrated?
Ответ
The more concentrated diagram contains more solute particles in that equal volume.
Карточка 167
Вопрос
How do differences in intermolecular attractions let distillation separate a liquid solution?
Ответ
They give the components different vapor pressures, so the vapor is enriched in the more volatile component.
Карточка 168
Вопрос
What comparison helps predict whether two liquids will be miscible?
Ответ
Liquids with similar types and strengths of intermolecular attractions are more likely to mix uniformly.
Карточка 169
Вопрос
How can an absorption spectrum help identify a substance?
Ответ
Its allowed energy gaps produce a characteristic pattern of absorbed wavelengths that can be compared with known spectra.
Карточка 170
Вопрос
How does absorbing or emitting a photon change an atom's or molecule's energy?
Ответ
Absorption raises the species' energy by exactly the photon energy; emission lowers it by the same amount.
Карточка 171
Вопрос
What macroscopic evidence can support that a chemical reaction occurred?
Ответ
Evidence can include gas formation, precipitate formation, a persistent color change, or an energy change, interpreted with particle-level changes.
Карточка 172
Вопрос
What does a net ionic equation include?
Ответ
Only the dissolved or reacting species that undergo chemical change; spectator ions are omitted.
Карточка 173
Вопрос
What must a correct particulate reaction diagram conserve?
Ответ
The number of atoms of every element and the total charge.
Карточка 174
Вопрос
What distinguishes a chemical change from a physical change?
Ответ
A chemical change rearranges bonds into new substances; a physical change alters state or arrangement without changing chemical identity.
Карточка 175
Вопрос
What does a balanced equation's coefficient ratio provide?
Ответ
The mole ratio among reacting and produced species.
Карточка 176
Вопрос
What is the equivalence point of a titration?
Ответ
The point where titrant and analyte have reacted in the stoichiometric ratio given by the balanced equation.
Карточка 177
Вопрос
What defines a precipitation reaction?
Ответ
Aqueous ions combine to form a sparingly soluble solid.
Карточка 178
Вопрос
What happens in a Brønsted–Lowry acid–base reaction?
Ответ
A proton transfers from the acid (donor) to the base (acceptor). In aqueous solution, H₂O can play either role.
Карточка 179
Вопрос
What does oxidation mean in a redox reaction?
Ответ
Loss of electrons and an increase in oxidation number.
Карточка 180
Вопрос
What particle-level change confirms that a process is chemical?
Ответ
Atoms rearrange into new combinations, producing substances with different compositions.
Карточка 181
Вопрос
Which ions are spectators when AgNO₃(aq) reacts with NaCl(aq)?
Ответ
Na⁺ and NO₃⁻. The net ionic reaction is Ag⁺(aq) + Cl⁻(aq) → AgCl(s).
Карточка 182
Вопрос
How does a particulate diagram reveal the limiting reactant?
Ответ
After forming the maximum product allowed by the ratio, none of the limiting reactant remains while excess reactant particles do.
Карточка 183
Вопрос
Is melting ice a chemical or physical change?
Ответ
A physical change. H₂O molecules remain H₂O while their arrangement and motion change.
Карточка 184
Вопрос
How is the limiting reactant identified from given amounts?
Ответ
Convert each reactant to the same product amount using the balanced equation; the smaller product amount identifies the limiting reactant.
Карточка 185
Вопрос
How does an endpoint differ from an equivalence point?
Ответ
The endpoint is an observed signal such as indicator color change; the equivalence point is the exact stoichiometric condition.
Карточка 186
Вопрос
How is complete combustion of a hydrocarbon in excess oxygen classified, and what products form?
Ответ
It is a redox combustion reaction that forms CO₂ and H₂O.
Карточка 187
Вопрос
What are the conjugate acid and conjugate base in NH₃ + H₂O ⇌ NH₄⁺ + OH⁻?
Ответ
NH₄⁺ is the conjugate acid of NH₃, and OH⁻ is the conjugate base of H₂O.
Карточка 188
Вопрос
What does reduction mean in a redox reaction?
Ответ
Gain of electrons and a decrease in oxidation number.
Карточка 189
Вопрос
Which common changes are physical rather than chemical?
Ответ
Phase changes and the formation or separation of mixtures are physical when each substance keeps its composition.
Карточка 190
Вопрос
How are strong soluble electrolytes written in a complete ionic equation?
Ответ
As separated aqueous ions; solids, liquids, gases, and weak electrolytes stay intact.
Карточка 191
Вопрос
A diagram starts with six A particles and four B₂ particles for 2A + B₂ → 2AB; what remains after completion?
Ответ
One B₂ remains. Six A consume three B₂ and form six AB.
Карточка 192
Вопрос
Why is dissolving NaCl in water normally classified as a physical change?
Ответ
Na⁺ and Cl⁻ separate and become hydrated, but retain their chemical identities. Removing the water recovers NaCl; the shift from ion–ion to ion–dipole attractions does not by itself form a new substance.
Карточка 193
Вопрос
What mass of AgCl can form from 25.0 mL of 0.200 M AgNO₃ mixed with excess Cl⁻?
Ответ
0.717 g AgCl. The 1:1 reaction gives 0.00500 mol AgCl; multiply by 143.32 g mol^-1.
Карточка 194
Вопрос
What calculation finds unknown analyte moles at equivalence?
Ответ
Use titrant moles, n = MV, then apply the balanced-reaction mole ratio.
Карточка 195
Вопрос
Which feature identifies an acid–base, redox, or precipitation reaction?
Ответ
Acid–base reactions transfer protons, redox reactions change oxidation numbers through electron transfer, and precipitation reactions form a sparingly soluble solid.
Карточка 196
Вопрос
What is the net ionic equation for strong acid–strong base neutralization?
Ответ
H⁺(aq) + OH⁻(aq) → H₂O(l).
Карточка 197
Вопрос
What is the oxidation number of sulfur in SO₄²⁻?
Ответ
+6. Four oxygens contribute -8 total, so sulfur must be +6 to give -2 overall.
Карточка 198
Вопрос
Why can gas bubbles alone be ambiguous evidence of reaction?
Ответ
Bubbles may also come from boiling or dissolved gas escaping, so the context and particle identities must support a chemical change.
Карточка 199
Вопрос
How is melting ice represented as a balanced physical-change equation?
Ответ
H₂O(s) → H₂O(l). The formula and atom count stay the same because only the physical state changes.
Карточка 200
Вопрос
What does a particle diagram show when no reaction occurs after two aqueous ionic solutions mix?
Ответ
All ions remain separated and solvated, with no new bonded particles, precipitate, or gas.
Карточка 201
Вопрос
Why is rusting iron a chemical change?
Ответ
Iron atoms form new iron-oxide substances through electron transfer and new bonding.
Карточка 202
Вопрос
For 2H₂O₂(aq) → 2H₂O(l) + O₂(g), what volume of O₂ forms from 0.100 mol H₂O₂ at 298 K and 1.00 atm?
Ответ
1.22 L O₂. The mole ratio gives 0.0500 mol O₂, then V = nRT/P.
Карточка 203
Вопрос
A 25.0 mL monoprotic acid sample requires 20.0 mL of 0.150 M NaOH; what is the acid concentration?
Ответ
0.120 M. At 1:1 equivalence, moles acid = 0.0200 L × 0.150 M, then divide by 0.0250 L.
Карточка 204
Вопрос
Which salts does the minimum solubility rule in this deck treat as soluble?
Ответ
All salts containing Na⁺, K⁺, NH₄⁺, or NO₃⁻ are treated as soluble in water.
Карточка 205
Вопрос
How are the strengths of a conjugate acid and its conjugate base related?
Ответ
A stronger acid has a weaker conjugate base, and a stronger base has a weaker conjugate acid.
Карточка 206
Вопрос
How are oxidation and reduction half-reactions combined into one balanced equation?
Ответ
Multiply them so electrons lost equal electrons gained, add the half-reactions, then cancel electrons and any identical species on both sides.
Карточка 207
Вопрос
How do molecular, complete ionic, and net ionic equations differ?
Ответ
Molecular equations keep compounds intact, complete ionic equations split strong soluble electrolytes, and net ionic equations remove spectators. All three conserve atoms and charge.
Карточка 208
Вопрос
How should coefficients change particle counts in a reaction diagram?
Ответ
They set whole-particle ratios while preserving each particle's chemical formula.
Карточка 209
Вопрос
Is separating a mixture by distillation a chemical or physical change?
Ответ
A physical change. Components change phase and location but keep their chemical identities.
Карточка 210
Вопрос
What equation results from Cu → Cu²⁺ + 2e⁻ and Ag⁺ + e⁻ → Ag?
Ответ
Cu + 2Ag⁺ → Cu²⁺ + 2Ag. Multiply the silver half-reaction by 2 and cancel 2e⁻; both atom counts and net charge then match.
Карточка 211
Вопрос
How is average reaction rate found from a reactant concentration?
Ответ
Use the negative concentration change divided by elapsed time, adjusted by its stoichiometric coefficient when comparing species rates.
Карточка 212
Вопрос
What does a rate law express?
Ответ
It shows how the measured rate depends on reactant concentrations. In rate = k[A]^m[B]^n, m and n are the orders in A and B, and m + n is the overall order.
Карточка 213
Вопрос
A plot of ln[A] versus time is linear; what is the order in A and its integrated rate law?
Ответ
First order: ln[A]t = ln[A]0 − kt, so the plot's slope is −k.
Карточка 214
Вопрос
What is an elementary reaction?
Ответ
A single step in a mechanism whose rate law follows directly from its reactant molecularity.
Карточка 215
Вопрос
What two collision conditions are needed for reaction?
Ответ
Sufficient collision energy and a productive molecular orientation.
Карточка 216
Вопрос
What does activation energy represent on a reaction-energy profile?
Ответ
The energy difference from the reactants to the transition state. The reaction coordinate tracks the step's structural progress, not elapsed time.
Карточка 217
Вопрос
What must the elementary steps of a valid mechanism do when added?
Ответ
Cancel intermediates and reproduce the overall balanced reaction.
Карточка 218
Вопрос
How is a proposed mechanism tested against kinetics?
Ответ
Its derived rate law must agree with the experimentally measured rate law.
Карточка 219
Вопрос
What does a pre-equilibrium approximation assume?
Ответ
A fast reversible step reaches equilibrium before a later slow step consumes its intermediate.
Карточка 220
Вопрос
What does each peak on a multistep energy profile represent?
Ответ
A transition state for one elementary step.
Карточка 221
Вопрос
How does a catalyst increase reaction rate?
Ответ
It provides an alternate mechanism with a lower activation-energy pathway.
Карточка 222
Вопрос
Why does crushing a solid reactant usually increase its reaction rate?
Ответ
Crushing increases exposed surface area, so more reactant particles can collide with the other reactant each second.
Карточка 223
Вопрос
How is reaction order found from initial-rate data?
Ответ
Compare trials where one reactant concentration changes while the others stay constant, then match the rate factor to the concentration factor.
Карточка 224
Вопрос
A plot of [A] versus time is linear; what is the order in A and its integrated rate law?
Ответ
Zero order: [A]t = [A]0 − kt, so the plot's slope is −k.
Карточка 225
Вопрос
What is the rate law for the elementary step 2A + B → products?
Ответ
rate = k[A]²[B]. This inference is valid because the step is elementary.
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Карточка 226
Вопрос
How does raising temperature change a Maxwell–Boltzmann energy distribution and reaction rate?
Ответ
The distribution shifts and broadens toward higher energies, so a larger fraction of collisions exceeds the activation-energy threshold and can react.
Карточка 227
Вопрос
How is ΔH read from a reaction-energy profile?
Ответ
ΔH = energy of products − energy of reactants.
Карточка 228
Вопрос
What is a reaction intermediate?
Ответ
A species formed in one mechanism step and consumed in a later step, so it cancels from the overall equation.
Карточка 229
Вопрос
Why can't overall reaction coefficients usually supply rate-law exponents?
Ответ
The overall equation hides the mechanism; exponents come from experiment unless the reaction is a stated elementary step.
Карточка 230
Вопрос
How does pre-equilibrium remove an intermediate from a rate law?
Ответ
Use the fast-step equilibrium relation to express the intermediate concentration in terms of stable reactants.
Карточка 231
Вопрос
What does each valley between peaks represent on a multistep profile?
Ответ
A reaction intermediate.
Карточка 232
Вопрос
Does a catalyst change ΔH or the equilibrium constant?
Ответ
No. It changes the pathway and rates, not reactant/product energies or the equilibrium composition.
Карточка 233
Вопрос
For 2A → B, how are disappearance of A and appearance of B related?
Ответ
Reaction rate = -(1/2)Δ[A]/Δt = Δ[B]/Δt.
Карточка 234
Вопрос
How do the units of k depend on a rate law's overall order?
Ответ
They must make the rate unit M s^-1: zero order uses M s^-1, first order s^-1, and second order M^-1 s^-1.
Карточка 235
Вопрос
A plot of 1/[A] versus time is linear; what is the order in A and its integrated rate law?
Ответ
Second order: 1/[A]t = 1/[A]0 + kt, so the plot's slope is +k.
Карточка 236
Вопрос
What is molecularity?
Ответ
The number of reacting particles in an elementary step, such as unimolecular or bimolecular.
Карточка 237
Вопрос
How does raising temperature affect k in the qualitative Arrhenius model?
Ответ
k increases, often sharply, because a larger fraction of collisions can reach the transition state. Arrhenius-equation calculations are outside this deck’s scope.
Карточка 238
Вопрос
A reactant falls from 0.80 M to 0.50 M in 30. s; what is its average disappearance rate to two significant figures?
Ответ
0.010 M s^-1. Use -(0.50 − 0.80) M ÷ 30. s.
Карточка 239
Вопрос
How does a catalyst differ from an intermediate in a mechanism?
Ответ
A catalyst is consumed early and regenerated later; an intermediate is formed early and consumed later.
Карточка 240
Вопрос
For 2NO₂ → NO₃ + NO (slow), followed by NO₃ + CO → NO₂ + CO₂ (fast), what rate law is predicted?
Ответ
rate = k[NO₂]². The first step is elementary and rate-limiting, so its molecularity sets the observed rate law.
Карточка 241
Вопрос
On a multistep reaction-energy profile, which feature often identifies the rate-determining step?
Ответ
The step with the largest activation barrier measured from its preceding valley to its peak.
Карточка 242
Вопрос
If changing [B] leaves rate unchanged, what is the order in B?
Ответ
Zero order, so [B]^0 = 1 in the measured rate law.
Карточка 243
Вопрос
What mechanism changes can binding, acid–base, or surface catalysis introduce?
Ответ
They can orient reactants, lower activation barriers, or create new bound, protonated, or deprotonated intermediates and elementary steps; the catalyst is regenerated.
Карточка 244
Вопрос
What is special about a first-order reaction's half-life?
Ответ
It is constant and independent of starting concentration: t1/2 = ln 2/k. Radioactive decay is a common first-order example.
Карточка 245
Вопрос
Why is a termolecular elementary collision uncommon?
Ответ
Three particles must collide simultaneously with suitable energy and orientation, which is much less probable than one- or two-particle events.
Карточка 246
Вопрос
On a reaction-energy profile, how are reverse activation energy, forward activation energy, and ΔH related?
Ответ
Ea,reverse = Ea,forward − ΔH. The reverse barrier is measured from products to the same transition state.
Карточка 247
Вопрос
Why can correct orientation matter even above the activation energy?
Ответ
The colliding reactive sites must align so old bonds can break and new bonds can form along the reaction pathway.
Карточка 248
Вопрос
How does detecting a proposed reaction intermediate affect a mechanism claim?
Ответ
It supports a mechanism that contains that intermediate, but it doesn't prove that mechanism is unique.
Карточка 249
Вопрос
For 2NO ⇌ N₂O₂ (fast equilibrium), followed by N₂O₂ + O₂ → 2NO₂ (slow), what observed rate law results?
Ответ
rate = kobs[NO]²[O₂]. Start with rate = k₂[N₂O₂][O₂], use [N₂O₂] = K[NO]² from the fast equilibrium, then substitute.
Карточка 250
Вопрос
What does the highest point of a one-step energy profile represent?
Ответ
The transition state, an unstable arrangement at the top of the activation barrier.
Карточка 251
Вопрос
What sign does q have for an endothermic system?
Ответ
Positive, because the system absorbs heat from the surroundings.
Карточка 252
Вопрос
How does an exothermic reaction appear on an enthalpy diagram?
Ответ
Products lie below reactants, so ΔH is negative.
Карточка 253
Вопрос
What condition defines thermal equilibrium?
Ответ
Objects in contact have the same temperature, so there is no net heat transfer.
Карточка 254
Вопрос
What equations relate heat capacity and temperature change to heat transfer?
Ответ
Use q = mcΔT with specific heat capacity, or q = nCₘΔT with molar heat capacity.
Карточка 255
Вопрос
Why is temperature constant during a phase-change plateau?
Ответ
Added or removed energy changes interparticle potential energy instead of average kinetic energy.
Карточка 256
Вопрос
What does ΔHrxn describe?
Ответ
The heat absorbed or released at constant pressure for the reaction exactly as written under the stated conditions.
Карточка 257
Вопрос
How is reaction enthalpy estimated from average bond enthalpies?
Ответ
ΔHrxn ≈ Σ(bonds broken) − Σ(bonds formed).
Карточка 258
Вопрос
What is the standard enthalpy of formation of an element in its standard state?
Ответ
Zero by definition.
Карточка 259
Вопрос
In a Hess’s law calculation, how should a step change when the target needs twice its reverse?
Ответ
Reverse the equation, double every coefficient, and multiply its ΔH by -2.
Карточка 260
Вопрос
How can energy cross a system boundary during a process?
Ответ
As heat or work. Heat transferred to or work done on the system increases its energy; heat transferred from or work done by the system decreases it.
Карточка 261
Вопрос
How does an endothermic reaction appear on an enthalpy diagram?
Ответ
Products lie above reactants, so ΔH is positive.
Карточка 262
Вопрос
How are heat gained by a system and heat lost by its surroundings related in an isolated setup?
Ответ
qsystem = -qsurroundings.
Карточка 263
Вопрос
In coffee-cup calorimetry, how is reaction heat related to solution heat?
Ответ
qrxn = -qsolution when calorimeter heat is negligible and pressure is constant.
Карточка 264
Вопрос
What heat is required to melt n moles at the melting point?
Ответ
q = nΔHfus.
Карточка 265
Вопрос
How does reversing a reaction change ΔH?
Ответ
It reverses the sign of ΔH.
Карточка 266
Вопрос
Why is breaking a bond endothermic?
Ответ
Energy must be supplied to separate atoms against their bonding attraction.
Карточка 267
Вопрос
How is ΔH°rxn calculated from standard enthalpies of formation?
Ответ
ΣνΔHf°(products) − ΣνΔHf°(reactants).
Карточка 268
Вопрос
How does multiplying an equation by 3 affect its ΔH?
Ответ
Multiply ΔH by 3 because enthalpy change scales with reaction amount.
Карточка 269
Вопрос
Why can an exothermic dissolution warm the solution?
Ответ
The solution warms because forming solute–solvent attractions releases more energy than is absorbed in separating the original particles. The net potential-energy decrease raises particle kinetic energy and temperature.
Карточка 270
Вопрос
Does an energy diagram's activation barrier determine ΔH?
Ответ
No. ΔH depends on reactant and product energy levels, while the barrier controls kinetics.
Карточка 271
Вопрос
Why does heat flow from a warmer object to a cooler object?
Ответ
Energy transfers through collisions until their average kinetic energies, and therefore temperatures, equalize.
Карточка 272
Вопрос
How much heat warms 100.0 g of water by 5.0°C?
Ответ
2.1 kJ. Use q = (100.0 g)(4.184 J g^-1 °C^-1)(5.0°C).
Карточка 273
Вопрос
How are the molar enthalpies of a phase change and its reverse related?
Ответ
They have equal magnitudes and opposite signs, such as ΔHcond = -ΔHvap and ΔHfreeze = -ΔHfus.
Карточка 274
Вопрос
How does doubling every coefficient in a thermochemical equation affect ΔH?
Ответ
It doubles ΔH.
Карточка 275
Вопрос
Why is forming a bond exothermic?
Ответ
Atoms move to a lower-potential-energy bonded arrangement and release energy.
Карточка 276
Вопрос
What formation equation defines ΔHf° for CO₂(g)?
Ответ
C(s, graphite) + O₂(g) → CO₂(g), forming exactly one mole from elements in standard states.
Карточка 277
Вопрос
What should happen to intermediate species when equations in a Hess’s law calculation are added?
Ответ
They cancel, leaving the target overall reaction.
Карточка 278
Вопрос
If the surroundings warm during a process, what is the likely sign of qsystem?
Ответ
Negative; the system likely released heat to the surroundings.
Карточка 279
Вопрос
For a profile with reactants at 40 kJ and products at 10 kJ, what is ΔH?
Ответ
-30 kJ for the reaction as drawn.
Карточка 280
Вопрос
Assuming no phase change, what determines the final temperature when two substances exchange heat in an insulated container?
Ответ
Energy conservation: q_warm + q_cool = 0. Use each substance's mass, heat capacity, and initial temperature to solve for the common final temperature.
Карточка 281
Вопрос
How would heat loss to the room affect an exothermic calorimetry result?
Ответ
The observed temperature rise is too small, so the calculated magnitude of released heat is too low.
Карточка 282
Вопрос
What heat expression covers warming a liquid without a phase change?
Ответ
q = mcΔT, not nΔHphase.
Карточка 283
Вопрос
If forming 1 mol of product has ΔH = -50 kJ mol^-1, what is q when 2 mol forms?
Ответ
-100 kJ. Use q = nΔH = (2 mol)(-50 kJ mol^-1).
Карточка 284
Вопрос
Breaking reactant bonds requires 500 kJ, and forming product bonds releases 650 kJ; what is the estimated ΔH?
Ответ
-150 kJ, from 500 − 650.
Карточка 285
Вопрос
For CO(g) + ½O₂(g) → CO₂(g), what is ΔH°rxn if ΔHf°[CO] = -110.5 and ΔHf°[CO₂] = -393.5 kJ mol^-1?
Ответ
-283.0 kJ. Use -393.5 - [-110.5 + ½(0)], since ΔHf°[O₂(g)] = 0.
Карточка 286
Вопрос
In a Hess’s law calculation, two valid steps have ΔH values +25 kJ and -60 kJ; what is the combined ΔH?
Ответ
-35 kJ, provided the equations add to the target reaction.
Карточка 287
Вопрос
Why is “bonds breaking releases energy” incorrect?
Ответ
Bond breaking absorbs energy; the overall reaction releases energy only when forming new bonds releases more than breaking old bonds requires.
Карточка 288
Вопрос
How would melting appear on an energy diagram?
Ответ
The liquid lies above the solid, so ΔHfus is positive; the diagram represents a physical, endothermic change.
Карточка 289
Вопрос
Can two objects at the same temperature exchange energy microscopically?
Ответ
Yes, but their energy transfers balance, so there is no net heat flow.
Карточка 290
Вопрос
Why must the calorimeter's heat capacity be included when it isn't negligible?
Ответ
The apparatus can absorb or release heat, so include q_cal = C_calΔT in the energy balance: q_process + q_solution + q_cal = 0.
Карточка 291
Вопрос
What makes chemical equilibrium dynamic?
Ответ
Forward and reverse reactions continue at equal rates even though macroscopic concentrations stay constant.
Карточка 292
Вопрос
For aA + bB ⇌ cC, what is the concentration-form expression for Q?
Ответ
Q = [C]^c / ([A]^a[B]^b), using current rather than necessarily equilibrium concentrations.
Карточка 293
Вопрос
What does K much greater than 1 indicate?
Ответ
Products predominate at equilibrium, though K says nothing about reaction speed.
Карточка 294
Вопрос
How does reversing a reaction change its equilibrium constant?
Ответ
K becomes 1/K.
Карточка 295
Вопрос
Can a reversible system reach equilibrium when it starts with only products?
Ответ
Yes, if the reverse reaction is possible. The equilibrium composition depends on temperature, initial amounts, and volume or pressure.
Карточка 296
Вопрос
How do Q and K predict reaction direction?
Ответ
Q < K shifts forward, Q > K shifts reverse, and Q = K means equilibrium.
Карточка 297
Вопрос
Which species are omitted from a heterogeneous equilibrium expression?
Ответ
Pure solids and pure liquids because their activities are effectively constant.
Карточка 298
Вопрос
How does increasing a dissolved reactant's concentration or a gaseous reactant's partial pressure affect equilibrium at constant temperature when other Q terms are initially unchanged?
Ответ
It lowers Q relative to K, so the system shifts toward products until Q = K again. Changing the amount of a pure solid or liquid omitted from Q does not cause this shift while that pure phase remains present.
Карточка 299
Вопрос
What does a flat concentration-time graph mean at equilibrium?
Ответ
Each concentration is constant, not necessarily equal to the others.
Карточка 300
Вопрос
For A ⇌ B in one fixed volume, a particulate model shows 16 A and 0 B initially, then 4 A and 12 B at equilibrium. What changed, what predominates, and what is Kc?
Ответ
The net change was forward: 12 A particles became 12 B particles. B predominates at equilibrium, and Kc = [B]/[A] = 12/4 = 3.0 because both counts come from the same fixed volume.
Карточка 301
Вопрос
What can Ksp tell you about a salt's solubility, and when can two Ksp values be compared directly?
Ответ
Ksp > 1 indicates a soluble salt. For salts with the same dissolution stoichiometry, a larger Ksp generally means greater molar solubility; across different stoichiometries, calculate molar solubility before comparing.
Карточка 302
Вопрос
What is the common-ion effect on solubility?
Ответ
Adding an ion already in the dissolution equilibrium usually decreases the solid's molar solubility.
Карточка 303
Вопрос
How does uniform dilution shift an aqueous equilibrium based on the stoichiometric powers in Q?
Ответ
It shifts toward the side with the larger sum of stoichiometric coefficients for dissolved species included in Q. If the sums are equal, dilution causes no shift by this effect; pure solids and liquids remain omitted.
Карточка 304
Вопрос
What happens if a reversible reaction starts with reactants only?
Ответ
The forward rate is initially largest; products form, the reverse rate grows, and the rates eventually become equal.
Карточка 305
Вопрос
What is the purpose of an ICE table?
Ответ
To organize initial, change, and equilibrium concentrations using reaction stoichiometry.
Карточка 306
Вопрос
Can a reaction with a very large K be slow?
Ответ
Yes. K describes thermodynamic equilibrium position, while rate depends on kinetics and activation energy.
Карточка 307
Вопрос
What happens to Q immediately after product concentration increases?
Ответ
Q increases; if it rises above K, the reaction shifts toward reactants.
Карточка 308
Вопрос
How does multiplying every reaction coefficient by 2 affect K?
Ответ
The new equilibrium constant is K².
Карточка 309
Вопрос
For A ⇌ B, Kc = 4.0 and initially [A] = 1.0 M and [B] = 0, what are the equilibrium concentrations?
Ответ
[A] = 0.20 M and [B] = 0.80 M. Let x form: Kc = x/(1.0 − x) = 4.0, so x = 0.80 M.
Карточка 310
Вопрос
What macroscopic properties stay constant at equilibrium?
Ответ
Properties such as concentration, color, and pressure remain constant when external conditions are fixed.
Карточка 311
Вопрос
How does decreasing volume shift a gaseous equilibrium?
Ответ
Toward the side with fewer moles of gas, if the two sides have different gaseous mole counts.
Карточка 312
Вопрос
For N₂ + 3H₂ ⇌ 2NH₃, what is Kc?
Ответ
Kc = [NH₃]² / ([N₂][H₂]³).
Карточка 313
Вопрос
For CaF₂(s) ⇌ Ca²⁺ + 2F⁻, how is Ksp written in terms of molar solubility s in pure water?
Ответ
Ksp = s(2s)² = 4s³ because [Ca²⁺] = s and [F⁻] = 2s.
Карточка 314
Вопрос
What does K much less than 1 indicate?
Ответ
Reactants predominate at equilibrium.
Карточка 315
Вопрос
How does decreasing a dissolved product's concentration or a gaseous product's partial pressure affect equilibrium when other Q terms are initially unchanged?
Ответ
It lowers Q and drives a net forward reaction until equilibrium returns. Changing the amount of a pure solid or liquid omitted from Q does not cause this shift while that phase remains.
Карточка 316
Вопрос
Does equilibrium mean the reaction has stopped?
Ответ
No. Both directions continue, but equal rates produce no net macroscopic change.
Карточка 317
Вопрос
Why does adding NaF reduce CaF₂ solubility?
Ответ
The added F⁻ raises Qsp, shifting the dissolution equilibrium toward solid CaF₂.
Карточка 318
Вопрос
For N₂ + 3H₂ ⇌ 2NH₃, what is Kp when P_N₂ = 0.50 atm, P_H₂ = 1.50 atm, and P_NH₃ = 0.25 atm?
Ответ
0.037. Use Kp = (P_NH₃)²/[(P_N₂)(P_H₂)³] = (0.25)²/[(0.50)(1.50)³]. Use equilibrium partial pressures directly; Kc↔Kp conversion isn't assessed.
Карточка 319
Вопрос
What happens to Q when a gaseous equilibrium mixture is compressed at constant temperature if products have fewer gas moles?
Ответ
Q falls relative to K, so the reaction shifts toward products.
Карточка 320
Вопрос
How do K and Q transform when a reaction is reversed, its coefficients are multiplied, or reactions are added?
Ответ
They follow the same algebra: reversing takes the reciprocal, multiplying every coefficient by c raises the value to the power c, and adding reactions multiplies their K or Q values.
Карточка 321
Вопрос
When is the small-x approximation acceptable?
Ответ
When x is small relative to the initial concentration and the final result confirms the neglected change is suitably small.
Карточка 322
Вопрос
What graph feature shows a disturbance followed by re-equilibration?
Ответ
A sudden or gradual concentration change followed by new constant plateaus while rates return to equality.
Карточка 323
Вопрос
If Q = 0.20 and K = 5.0, which direction is favored next?
Ответ
Forward, because Q < K.
Карточка 324
Вопрос
At equilibrium, are reactant and product concentrations equal?
Ответ
Not necessarily. They are constant, while forward and reverse rates are equal.
Карточка 325
Вопрос
CaF₂ has Ksp = 3.2 × 10^-11 in pure water; what is its molar solubility?
Ответ
2.0 × 10^-4 M. If the molar solubility is s, then [Ca²⁺] = s, [F⁻] = 2s, and Ksp = 4s³.
Карточка 326
Вопрос
For N₂ + 3H₂ ⇌ 2NH₃, how is Qp written?
Ответ
Qp = (P_NH₃)²/[(P_N₂)(P_H₂)³], using the current partial pressures rather than necessarily equilibrium values.
Карточка 327
Вопрос
How does heating shift an endothermic forward reaction?
Ответ
Toward products, and K increases because temperature changes the equilibrium constant.
Карточка 328
Вопрос
Why do both forward and reverse rates change as equilibrium is approached?
Ответ
As reactant and product concentrations change, the collision frequencies for the two directions change until their rates match.
Карточка 329
Вопрос
CaF₂ has Ksp = 3.2 × 10^-11. What is its molar solubility in 0.10 M NaF?
Ответ
About 3.2 × 10^-9 M. With [F⁻] ≈ 0.10 M, Ksp = [Ca²⁺][F⁻]² gives s = (3.2 × 10^-11)/(0.10)². The common ion lowers solubility but does not change Ksp at constant temperature.
Карточка 330
Вопрос
What concentration data must be used to calculate Kc?
Ответ
Equilibrium concentrations, each raised to its stoichiometric coefficient and excluding pure solids and liquids.
Карточка 331
Вопрос
What is a Brønsted–Lowry acid?
Ответ
A proton donor.
Карточка 332
Вопрос
How is pH defined?
Ответ
pH = -log[H₃O⁺].
Карточка 333
Вопрос
What is Ka for HA + H₂O ⇌ H₃O⁺ + A⁻?
Ответ
Ka = [H₃O⁺][A⁻]/[HA].
Карточка 334
Вопрос
How does stabilizing a base affect its basicity and the strength of its conjugate acid?
Ответ
It makes the base weaker and its conjugate acid stronger. A more stable base is less willing to accept H⁺.
Карточка 335
Вопрос
What is a Brønsted–Lowry base?
Ответ
A proton acceptor.
Карточка 336
Вопрос
At 25°C, what are Kw and the relationship between pH and pOH?
Ответ
Kw = [H₃O⁺][OH⁻] = 1.0 × 10^-14. Taking negative logarithms gives pH + pOH = 14.00.
Карточка 337
Вопрос
What is Kb for B + H₂O ⇌ BH⁺ + OH⁻?
Ответ
Kb = [BH⁺][OH⁻]/[B].
Карточка 338
Вопрос
Why can lowering pH increase the solubility of a salt containing a basic anion?
Ответ
H₃O⁺ consumes the anion, pulling the dissolution equilibrium toward more dissolved ions.
Карточка 339
Вопрос
What are conjugate acid–base pairs?
Ответ
Species that differ by exactly one proton.
Карточка 340
Вопрос
What is the pH of 1.0 × 10^-3 M HCl?
Ответ
3.00, assuming complete dissociation and negligible water contribution.
Карточка 341
Вопрос
How are pKa and pKb defined?
Ответ
pKa = -log Ka, and pKb = -log Kb.
Карточка 342
Вопрос
Why does acid strength increase across a row of comparable hydrides?
Ответ
Increasing electronegativity stabilizes the conjugate base and polarizes the H–A bond.
Карточка 343
Вопрос
What is an amphiprotic species?
Ответ
A species that can donate or accept a proton, such as HCO₃⁻.
Карточка 344
Вопрос
What amounts remain after a limited amount of strong base partially neutralizes weak acid HA?
Ответ
Subtract the reacted moles from HA and form the same number of moles of A⁻. The result gives the remaining HA and formed A⁻ amounts before any equilibrium or buffer-pH calculation.
Карточка 345
Вопрос
How are Ka, Kb, pKa, and pKb related for a conjugate pair at 25°C?
Ответ
KaKb = Kw = 1.0 × 10^-14, and pKa + pKb = pKw = 14.00.
Карточка 346
Вопрос
When does pH have little effect on a salt's solubility?
Ответ
When neither dissolved ion reacts appreciably with H₃O⁺ or OH⁻.
Карточка 347
Вопрос
How does H₂O act in HCl + H₂O → H₃O⁺ + Cl⁻ and in NH₃ + H₂O ⇌ NH₄⁺ + OH⁻?
Ответ
It acts as a base in the first reaction by accepting H⁺, and as an acid in the second by donating H⁺.
Карточка 348
Вопрос
After mixing weak base B with strong acid, what controls the final solution in the three stoichiometric regimes?
Ответ
Excess B leaves a B/BH⁺ buffer; equimolar amounts leave BH⁺, so the solution is acidic; excess strong acid sets the pH from the remaining H₃O⁺.
Карточка 349
Вопрос
What two components make a typical weak-acid buffer?
Ответ
A weak acid and a significant amount of its conjugate base.
Карточка 350
Вопрос
What do the successive half-equivalence pH values approximate in a diprotic weak-acid titration?
Ответ
The first approximates pKa₁ and the second approximates pKa₂ because each conjugate pair has equal concentrations at its half-equivalence point.
Карточка 351
Вопрос
Which acid is stronger, one with pKa 2 or pKa 5?
Ответ
The acid with pKa 2; lower pKa means larger Ka.
Карточка 352
Вопрос
What is the Henderson–Hasselbalch equation?
Ответ
pH = pKa + log([A⁻]/[HA]).
Карточка 353
Вопрос
Why are larger binary hydrides down a group often stronger acids?
Ответ
The H–A bond becomes weaker as the central atom grows, so proton release is easier.
Карточка 354
Вопрос
What mainly determines buffer capacity?
Ответ
The concentrations of both members of the conjugate acid–base pair. Increasing both concentrations at a fixed ratio increases capacity without changing pH; capacity is best balanced for added acid and base when their concentrations are similar.
Карточка 355
Вопрос
Why does acid increase CaCO₃ solubility?
Ответ
H₃O⁺ converts CO₃²⁻ to HCO₃⁻ or carbonic acid species, reducing free carbonate and driving more CaCO₃ to dissolve.
Карточка 356
Вопрос
What does pH < pKa imply for a weak-acid pair?
Ответ
The protonated form HA predominates over A⁻.
Карточка 357
Вопрос
What happens when stoichiometrically equal amounts of a monoprotic weak acid and strong base are mixed?
Ответ
The weak acid is consumed to its conjugate base; at equivalence, the solution isn't a buffer containing both forms.
Карточка 358
Вопрос
What is [H₃O⁺] when pH = 4.50?
Ответ
3.2 × 10^-5 M, from [H₃O⁺] = 10^-pH.
Карточка 359
Вопрос
What is the pH of 0.010 M Ba(OH)₂ at 25°C?
Ответ
About 12.30. Complete dissociation gives [OH⁻] = 0.020 M, so pOH = 1.70. At 25°C, pH + pOH = 14.00, so pH = 12.30.
Карточка 360
Вопрос
How does a buffer respond to a small amount of added strong acid?
Ответ
Its conjugate base consumes H⁺, converting to the weak acid and limiting the pH change.
Карточка 361
Вопрос
Why is the equivalence-point solution basic in a monoprotic weak-acid–strong-base titration?
Ответ
The conjugate base produced at equivalence reacts with water to form OH⁻, so the pH is above neutral—above 7.00 at 25°C.
Карточка 362
Вопрос
How is percent ionization calculated for a weak acid or weak base?
Ответ
For HA, use ([H₃O⁺]equilibrium ÷ [HA]initial) × 100%. For B, use ([BH⁺]equilibrium ÷ [B]initial) × 100%, under the usual monoprotic setup.
Карточка 363
Вопрос
When is Henderson–Hasselbalch useful for an initial buffer-pH calculation?
Ответ
Use it when both members of a conjugate acid–base pair are present in meaningful amounts, including after in-scope stoichiometry creates a buffer. Calculating the pH change after acid or base is added to an existing buffer is outside this deck’s scope.
Карточка 364
Вопрос
Why does adding oxygen atoms usually strengthen oxyacids with the same central atom?
Ответ
Extra oxygens withdraw electron density and delocalize negative charge in the conjugate base.
Карточка 365
Вопрос
A prepared buffer is accidentally diluted to twice its intended volume; what happens to its pH and capacity?
Ответ
Its pH stays nearly the same, and its capacity per liter is halved because both component concentrations halve. The total neutralizing moles in the sample remain unchanged.
Карточка 366
Вопрос
How does adding OH⁻ affect Mg(OH)₂ solubility?
Ответ
It decreases solubility through the common-ion effect, shifting Mg(OH)₂(s) ⇌ Mg²⁺ + 2OH⁻ toward the solid.
Карточка 367
Вопрос
A buffer has equal [A⁻] and [HA]; what is its pH?
Ответ
pH = pKa because log(1) = 0.
Карточка 368
Вопрос
How should a weak acid–strong base mixture be solved before equivalence?
Ответ
First use mole stoichiometry; if both HA and A⁻ remain, use the resulting buffer relation.
Карточка 369
Вопрос
Why can pure neutral water have a pH other than 7.00?
Ответ
Kw changes with temperature. Neutrality means [H₃O⁺] = [OH⁻], while pH = 7.00 only when Kw = 1.0 × 10^-14 at 25°C.
Карточка 370
Вопрос
25.0 mL of 0.200 M HCl is diluted to 100.0 mL; what is the pH?
Ответ
1.301. Dilution gives [H₃O⁺] = (0.200 M)(25.0 mL)/(100.0 mL) = 0.0500 M, so pH = -log(0.0500).
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Вопрос
How does a buffer respond to a small amount of added strong base?
Ответ
The weak acid consumes OH⁻, forming conjugate base and water.
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Вопрос
How do you find the final pH after mixing a strong acid and strong base at 25°C?
Ответ
Use H₃O⁺ + OH⁻ → 2H₂O and compare their moles. Divide excess H₃O⁺ or OH⁻ by the total volume, then calculate pH or pOH from that excess concentration. Equal moles give pH 7.00 at 25°C.
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Вопрос
What distinguishes acid strength from acid concentration?
Ответ
Strength is the equilibrium tendency to donate H⁺, reflected by Ka or pKa; concentration is the amount of acid per solution volume.
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Вопрос
If [A⁻]/[HA] = 10, how does pH compare with pKa?
Ответ
pH = pKa + 1 because log 10 = 1.
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Вопрос
Which conjugate base is more stable, one with localized or resonance-delocalized charge?
Ответ
The resonance-delocalized conjugate base, which generally corresponds to the stronger acid.
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Вопрос
Which 1.0 L buffer has greater capacity: 1.0 mol each of HA/A⁻ or 0.10 mol each at the same ratio?
Ответ
The 1.0 mol pair; both have the same initial pH, but the larger amounts neutralize more added acid or base.
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Вопрос
For BHX(s) ⇌ BH⁺ + X⁻, why can raising pH increase the salt's solubility?
Ответ
OH⁻ consumes BH⁺ to form B and H₂O, so dissolution shifts right to replace BH⁺. This is a qualitative prediction, not a pH-dependent solubility calculation.
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Вопрос
What does pH > pKa imply for a weak-acid pair?
Ответ
The deprotonated form A⁻ predominates over HA.
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Вопрос
For HA + B ⇌ A⁻ + BH⁺, which side is favored when pKa(HA) = 4 and pKa(BH⁺) = 9?
Ответ
Products are favored. Proton transfer moves toward the weaker acid–base pair, and K ≈ 10^(9 − 4) = 10^5.
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Вопрос
What is the pOH when [OH⁻] = 2.5 × 10^-4 M?
Ответ
3.60, from -log(2.5 × 10^-4).
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Вопрос
What is the pH of 0.100 M HA when Ka = 1.0 × 10^-5?
Ответ
About 3.00. The ICE setup gives Ka = x²/(0.100 − x); x ≈ 1.0 × 10^-3 M, and the 1.0% change validates the approximation.
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Вопрос
Why does a buffer fail after too much strong acid is added?
Ответ
Its conjugate base is depleted, so added H⁺ is no longer consumed effectively.
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Вопрос
What do two clear equivalence regions on an acid titration curve suggest?
Ответ
At least two distinguishable titratable protons; on a clean ideal curve with exactly two equivalence regions, this is consistent with a diprotic acid.
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Вопрос
A buffer has pKa 4.8 and [A⁻]/[HA] = 0.10; what is pH?
Ответ
3.8, from 4.8 + log(0.10).
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Вопрос
Why is HCl stronger than HF in water despite F being more electronegative?
Ответ
The H–F bond is much stronger; bond strength dominates this down-group binary-acid comparison.
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Вопрос
Why does percent ionization increase when a weak acid is diluted?
Ответ
Dilution shifts ionization toward more particles, so a larger fraction ionizes even though [H₃O⁺] decreases.
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Вопрос
A buffer contains more HA than A⁻. Which addition can it neutralize in greater amount: strong acid or strong base?
Ответ
Strong base. The larger HA reserve consumes more added OH⁻; a buffer with more A⁻ than HA instead has greater capacity for added strong acid.
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Вопрос
Why can removing a basic anion increase a salt's molar solubility without changing Ksp?
Ответ
The equilibrium shifts to replace the consumed ion; Ksp remains fixed at the same temperature.
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Вопрос
Why can an acid–base indicator change color as pH changes?
Ответ
Its protonated and deprotonated forms have different colors or other observable properties, and their relative amounts change with pH.
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Вопрос
What buffer results from mixing 1.0 mol HA with 0.40 mol OH⁻?
Ответ
0.60 mol HA and 0.40 mol A⁻ remain, forming a buffer before any equilibrium calculation.
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Вопрос
What is the pH of 0.200 M weak base B when Kb = 2.0 × 10^-5 at 25°C?
Ответ
About 11.30. The ICE setup gives Kb = x²/(0.200 − x); x ≈ 2.0 × 10^-3 M OH⁻, and the 1.0% change validates the approximation.
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Вопрос
Why does a weak acid alone not make an effective buffer?
Ответ
It lacks a substantial conjugate-base reserve to consume added strong acid.
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Вопрос
What controls pH after excess strong base passes equivalence?
Ответ
The concentration of excess OH⁻ after accounting for reaction stoichiometry and total volume.
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Вопрос
How should an indicator be chosen for a titration?
Ответ
Its color-change range should fall within the steep pH change near the equivalence point.
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Вопрос
How can a measured pH and known pKa give a conjugate-base/acid ratio?
Ответ
Rearrange Henderson–Hasselbalch: [A⁻]/[HA] = 10^(pH − pKa).
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Вопрос
Can a weak base and its conjugate acid form a buffer?
Ответ
Yes, when both are present in significant amounts.
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Вопрос
For equal-volume buffers with the same conjugate-base/acid ratio, how does adding the same amount of strong acid affect a more concentrated versus less concentrated buffer?
Ответ
The concentrated buffer changes pH less because it has greater capacity.
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Вопрос
How does equivalence-point pH compare for strong acid–strong base, weak acid–strong base, and weak base–strong acid titrations at 25°C?
Ответ
Strong acid–strong base: pH 7.00. Weak acid–strong base: above 7.00 because the conjugate base reacts with water. Weak base–strong acid: below 7.00 because the conjugate acid reacts with water.
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Вопрос
Why should mole ratios replace concentration ratios after mixing buffer solutions?
Ответ
Both components share the same final volume, so that volume cancels in [A⁻]/[HA].
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Вопрос
How does adding a little strong acid change a buffer's conjugate-base and conjugate-acid amounts?
Ответ
The conjugate base decreases and its conjugate acid increases by the amount of strong acid consumed.
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Вопрос
What does entropy measure qualitatively?
Ответ
The dispersal of matter and energy among available microstates.
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Вопрос
How is standard reaction entropy calculated?
Ответ
ΔS°rxn = ΣνS°(products) − ΣνS°(reactants).
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Вопрос
What equation gives ΔG° from ΔH° and ΔS°, and what standard states do the degree symbols assume?
Ответ
ΔG° = ΔH° − TΔS°. The standard states are pure substances, 1.0 M solutions, and gases at 1 atm or 1 bar; T is in kelvins and energy units must match.
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Вопрос
Does thermodynamic favorability guarantee a fast reaction?
Ответ
No. A favorable reaction can be slow when its activation barrier is large.
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Вопрос
What is ΔG at equilibrium?
Ответ
Zero under the current conditions because there is no net driving force.
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Вопрос
Why can an endothermic dissolution still be thermodynamically favorable?
Ответ
A sufficiently positive entropy change can make TΔS exceed positive ΔH, giving negative ΔG.
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Вопрос
How can an unfavorable reaction be driven by a favorable one?
Ответ
Couple them so their equations and ΔG values add to a negative overall ΔG.
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Вопрос
Where does oxidation occur in every electrochemical cell?
Ответ
At the anode.
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Вопрос
How are standard cell potential and standard free energy related?
Ответ
ΔG° = -nFE°cell.
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Вопрос
What equation gives cell potential under nonstandard conditions?
Ответ
E = E° − (RT/nF) ln Q. When Q = 1, ln Q = 0, so E = E°.
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Вопрос
How is electrical charge related to current and time?
Ответ
q = It.
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Вопрос
Which phase has greater molar entropy, liquid water or ice at the same temperature?
Ответ
Liquid water because its molecules have more accessible arrangements and motion.
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Вопрос
Do elements in their standard states have zero standard molar entropy?
Ответ
No. Their ΔHf° is zero, but their absolute S° values are positive above 0 K.
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Вопрос
How do the four ΔH° and ΔS° sign combinations determine thermodynamic favorability across temperature?
Ответ
ΔH° < 0 and ΔS° > 0 is favorable at every temperature; ΔH° > 0 and ΔS° < 0 is thermodynamically unfavored at every temperature. If both are positive, favorability requires high temperature; if both are negative, it requires low temperature.
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Вопрос
What does it indicate when a thermodynamically favored process does not occur at a measurable rate?
Ответ
It is under kinetic control, commonly because of a high activation energy; no measurable reaction does not mean the system is at equilibrium.
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Вопрос
How are ΔG° and K related?
Ответ
ΔG° = -RT ln K.
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Вопрос
What two contributions compete in dissolving an ionic solid?
Ответ
Enthalpy changes from separating and solvating particles, and entropy changes from their new dispersal and solvent organization.
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Вопрос
What must cancel when coupled reactions are added?
Ответ
Shared intermediates, leaving the desired net reaction.
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Вопрос
Where does reduction occur in every electrochemical cell?
Ответ
At the cathode.
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Вопрос
What sign of E°cell indicates a favorable standard galvanic reaction?
Ответ
Positive E°cell, corresponding to negative ΔG°.
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Вопрос
If Q increases for a galvanic reaction, how does E change at fixed temperature?
Ответ
E decreases according to the Nernst equation. Le Châtelier's principle does not apply to an operating cell away from equilibrium; use Q and Nernst reasoning instead.
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Вопрос
How are moles of electrons found from charge?
Ответ
Moles e⁻ = q/F, where F ≈ 96485 C mol^-1 e⁻.
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Вопрос
How does producing more gas particles usually affect system entropy?
Ответ
It increases entropy because the particles have more positional microstates.
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Вопрос
Can a dissolution with negative ΔH be unfavorable?
Ответ
Yes. A sufficiently negative entropy change at the stated temperature can make ΔG positive.
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Вопрос
When can a process with ΔH > 0 and ΔS > 0 become favorable?
Ответ
At sufficiently high temperature, when TΔS exceeds ΔH.
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Вопрос
How does a catalyst affect ΔG?
Ответ
It does not change ΔG; it lowers the activation barrier for both directions.
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Вопрос
For A → B, ΔGf°(A) = -50 kJ mol^-1 and ΔGf°(B) = -80 kJ mol^-1. What is ΔG°rxn?
Ответ
-30 kJ mol^-1. Use ΣνΔGf°(products) − ΣνΔGf°(reactants) = -80 − (-50).
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Вопрос
Why can dissolving a gas in a liquid have a negative entropy change?
Ответ
Gas particles lose much of their translational freedom when confined and solvated in the liquid.
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Вопрос
If coupled steps have ΔG values +20 kJ and -35 kJ, what is overall ΔG?
Ответ
-15 kJ, so the combined process is thermodynamically favorable under those conditions.
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Вопрос
What role does each half-cell solution play in an electrochemical cell?
Ответ
It supplies dissolved redox species at an electrode interface and carries ions within its compartment. Separate compartments prevent direct mixing while the external circuit and salt bridge connect the half-cells.
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Вопрос
How is E°cell found from standard reduction potentials?
Ответ
E°cell = E°cathode − E°anode, using both tabulated values as reductions.
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Вопрос
How does a cell's potential magnitude change as Q approaches or moves away from K, and what is E at equilibrium?
Ответ
|E| falls toward zero as Q approaches K and grows as the system moves farther from equilibrium. At equilibrium, Q = K and E = 0.
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Вопрос
How many moles of electrons pass when 1.93 × 10^5 C flows?
Ответ
2.00 mol e⁻, from q/F.
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Вопрос
How does a salt bridge maintain charge balance in a galvanic cell?
Ответ
Anions migrate toward the anode compartment and cations toward the cathode compartment, countering the net charge imbalances created by the two half-reactions.
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Вопрос
Why does raising a substance's temperature generally increase its entropy?
Ответ
Energy spreads across more accessible particle energy states, increasing the number of possible microscopic arrangements.
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Вопрос
When can a process with ΔH < 0 and ΔS < 0 be favorable?
Ответ
At sufficiently low temperature, where the unfavorable -TΔS term is small.
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Вопрос
Why can diamond persist even though graphite is more stable at standard conditions?
Ответ
Conversion has a large activation barrier, so diamond is kinetically persistent.
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Вопрос
What do the external circuit and measuring device do in an electrochemical cell?
Ответ
The circuit carries electrons from anode to cathode; a voltmeter measures potential difference, while an ammeter in series measures current.
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Вопрос
At constant temperature, how does increasing the volume available to a gas affect its entropy?
Ответ
Entropy increases because the gas particles can occupy more positions in the larger space, so more microstates are accessible.
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Вопрос
How does reversing one coupled reaction affect its ΔG?
Ответ
It reverses the sign of that reaction's ΔG.
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Вопрос
Why is n required in ΔG° = -nFE°?
Ответ
It is the moles of electrons transferred per balanced reaction, linking charge flow to reaction extent.
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Вопрос
What makes an electrolytic cell operate?
Ответ
An external power source drives a thermodynamically unfavorable redox reaction; oxidation still occurs at the anode and reduction at the cathode.
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Вопрос
In an Mⁿ⁺/M concentration cell, which half-cell is the anode: the dilute or concentrated ion solution?
Ответ
The dilute half-cell. Oxidation produces Mⁿ⁺ there, while reduction consumes Mⁿ⁺ in the concentrated half-cell, so electrons flow from dilute to concentrated as the concentrations move toward equality.
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Вопрос
How is deposited metal mass found from current and time?
Ответ
Find q = It, convert q/F to moles e⁻, use the half-reaction ratio to moles metal, then multiply by molar mass.
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Вопрос
Given product S° total 500 J mol^-1 K^-1 and reactant total 420 J mol^-1 K^-1, what is ΔS°?
Ответ
+80 J mol^-1 K^-1.
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Вопрос
How do electrode masses change in a Zn–Cu galvanic cell?
Ответ
The Zn anode loses mass as Zn → Zn²⁺ + 2e⁻, while the Cu cathode gains mass as Cu²⁺ + 2e⁻ → Cu.
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Вопрос
What is ΔG° when ΔH° = 50 kJ mol^-1, ΔS° = 0.200 kJ mol^-1 K^-1, and T = 300 K?
Ответ
-10 kJ mol^-1, from ΔG° = 50 − (300)(0.200).
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Вопрос
Why can temperature change a solid's solubility?
Ответ
Temperature changes the balance of ΔH and TΔS, so it changes the free energy of dissolution and the equilibrium constant.
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Вопрос
What does the size of ΔG° relative to RT imply about K?
Ответ
ΔG° near zero gives K near 1. When |ΔG°| is much larger than RT, K is far from 1: negative ΔG° gives K ≫ 1, while positive ΔG° gives K ≪ 1.
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Вопрос
Bubbles form at an inert cathode in acidic solution; which half-reaction can explain them?
Ответ
2H⁺ + 2e⁻ → H₂(g). Gas evolution at the cathode can be direct evidence of reduction.

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