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.
Über dieses Lernkartenset
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.
Karten in diesem Lernkartenset
Karte 1
Frage
What does one mole count?
Antwort
Exactly 6.02214076 × 10^23 representative particles.
Karte 2
Frage
What does a peak in an element's mass spectrum represent?
Antwort
An isotope with a particular mass-to-charge ratio; for singly charged monatomic ions, the position tracks isotopic mass.
Karte 3
Frage
What does an empirical formula show?
Antwort
The lowest whole-number ratio of the elements' atoms in a compound.
Karte 4
Frage
How does a mixture differ from a pure substance at the particle level?
Antwort
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.
Karte 5
Frage
Which particles make up an atom's nucleus?
Antwort
Protons and neutrons. Electrons occupy the space outside the nucleus.
Karte 6
Frage
What does a larger binding energy on a PES spectrum mean?
Antwort
More energy is required to remove that electron, so it is held more strongly by the nucleus.
Karte 7
Frage
How does atomic radius generally change across a period and down a group?
Antwort
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.
Karte 8
Frage
What typical ion charge do Group 1 metals form?
Antwort
+1, by losing their one valence electron.
Karte 9
Frage
How do you convert moles to particles?
Antwort
Multiply by Avogadro's number: particles = moles × 6.022 × 10^23 mol^-1.
Karte 10
Frage
How is average atomic mass estimated from isotope data?
Antwort
Add each isotopic mass multiplied by its fractional abundance.
Karte 11
Frage
How is an element's mass percent in a compound calculated?
Antwort
Divide the mass contributed by that element by the compound's molar mass, then multiply by 100%.
Karte 12
Frage
How can measured elemental composition reveal a sample's purity?
Antwort
Compare the measured mass fraction with the fraction expected for the pure compound; a mismatch indicates another component.
Karte 13
Frage
How do you build a ground-state electron configuration with the Aufbau principle?
Antwort
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.
Karte 14
Frage
What does the relative area or height of an ideal PES peak indicate?
Antwort
The relative number of electrons in the corresponding subshell.
Karte 15
Frage
How does first ionization energy generally change across a period and down a group?
Antwort
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.
Karte 16
Frage
Why do elements in the same group form similar compounds?
Antwort
Their ground-state valence patterns repeat, including which outer subshells are full or partly full. That leads to similar bonding and typical ion charges.
Karte 17
Frage
How do you convert a sample's mass to moles?
Antwort
Divide its mass by its molar mass: n = m/M.
Karte 18
Frage
Which mass-spectrum interpretation lies outside the usual single-element model used in this deck?
Antwort
Assigning peaks in mixtures or peaks from multiply charged or polyatomic species; the standard model uses singly charged monatomic ions of one element.
Karte 19
Frage
What does the law of definite proportions state?
Antwort
Every pure sample of a given compound has the same element mass ratios.
Karte 20
Frage
Why can two samples of the same mixture have different compositions?
Antwort
Mixture components are physically combined, so their relative amounts are not fixed by a chemical formula.
Karte 21
Frage
How does Coulomb's law connect charge and separation to attraction?
Antwort
Attraction grows with the magnitude of the charge product and decreases with the square of the separation distance.
Karte 22
Frage
Which PES electrons usually appear at the highest binding energy?
Antwort
Core electrons closest to the nucleus, because they feel the strongest nuclear attraction.
Karte 23
Frage
How does electron affinity generally change across a period and down a group?
Antwort
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.
Karte 24
Frage
Why are alkali metals generally more reactive down the group?
Antwort
Their valence electron is farther from the nucleus and easier to remove.
Karte 25
Frage
How many moles are in 18.0 g of H₂O?
Antwort
About 0.999 mol. Use 18.0 g ÷ 18.02 g mol^-1.
Karte 26
Frage
An element is 75% isotope 10 and 25% isotope 11; what is its average atomic mass?
Antwort
10.25 u. Calculate (0.75 × 10) + (0.25 × 11).
Karte 27
Frage
A compound is 40.0% C, 6.7% H, and 53.3% O by mass; what is its empirical formula?
Antwort
CH₂O. For a 100 g sample, convert each mass to moles and divide by the smallest amount.
Karte 28
Frage
A 10.0 g impure sample contains 8.5 g of the target compound; what is its mass-percent purity?
Antwort
85%. Calculate (8.5 g ÷ 10.0 g) × 100%.
Karte 29
Frage
Which electrons are removed first when a transition metal forms a cation?
Antwort
Electrons in the occupied orbital with the highest principal quantum number: 4s before 3d. For example, Fe²⁺ is [Ar] 3d⁶.
Karte 30
Frage
A PES spectrum has peaks proportional to 2, 2, and 6 electrons; which configuration fits?
Antwort
1s² 2s² 2p⁶, the configuration of Ne.
Karte 31
Frage
How does electronegativity generally change across a period and down a group?
Antwort
It increases from left to right across a period and decreases down a group as atomic size and shielding increase.
Karte 32
Frage
What empirical formula results from Al³⁺ and O²⁻?
Antwort
Al₂O₃, because two Al³⁺ ions balance three O²⁻ ions.
Karte 33
Frage
How does a particle's mass in atomic mass units relate to its molar mass?
Antwort
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.
Karte 34
Frage
What does the tallest isotope peak usually indicate in a simple mass spectrum?
Antwort
The most abundant isotope, assuming comparable detection response and singly charged ions.
Karte 35
Frage
How much oxygen is present in 25.0 g of a compound that is 32.0% oxygen by mass?
Antwort
8.00 g O. Multiply 25.0 g by 0.320.
Karte 36
Frage
What does a particle diagram with two unbonded species in changing ratios represent?
Antwort
A mixture, because more than one particle type is present and the ratio is not fixed in a formula unit.
Karte 37
Frage
What distinguishes valence electrons from core electrons?
Antwort
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.
Karte 38
Frage
Why can PES peak groups reveal an atom's occupied subshells?
Antwort
Electrons in different subshells require distinct removal energies, producing separate binding-energy groups.
Karte 39
Frage
How do ion radii compare with neutral atoms and within an isoelectronic series?
Antwort
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.
Karte 40
Frage
What formula is expected for a compound between a Group 2 metal M and a Group 17 nonmetal X?
Antwort
MX₂, because M forms M²⁺ and X forms X⁻.
Karte 41
Frage
When is a covalent bond considered nonpolar?
Antwort
When the bonded atoms have identical or very similar electronegativities, so the shared electron density is distributed approximately evenly.
Karte 42
Frage
Why does a bonded pair of atoms have an equilibrium bond length?
Antwort
At that separation, attractive and repulsive interactions balance at minimum potential energy.
Karte 43
Frage
How are particles arranged in an ionic solid?
Antwort
Cations and anions occupy a repeating three-dimensional lattice held by electrostatic attraction.
Karte 44
Frage
What model explains bonding in a metal?
Antwort
Positive metal cores are held together by attraction to mobile, delocalized valence electrons.
Karte 45
Frage
How do you construct a Lewis diagram?
Antwort
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.
Karte 46
Frage
What does resonance mean in a molecule or ion?
Antwort
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.
Karte 47
Frage
What determines molecular shape in VSEPR theory?
Antwort
Electron domains around the central atom arrange to minimize repulsions.
Karte 48
Frage
How does an ionic bond differ from a covalent bond?
Antwort
Ionic bonding is attraction among oppositely charged ions in an extended structure; covalent bonding uses shared electron density between atoms.
Karte 49
Frage
What happens to potential energy when bonded atoms are pushed much closer than equilibrium?
Antwort
Potential energy rises sharply because nucleus–nucleus and electron–electron repulsions dominate.
Karte 50
Frage
Why are many ionic solids brittle?
Antwort
A shifted lattice can align like charges, creating strong repulsion that splits the crystal.
Karte 51
Frage
What molecular shapes arise from two electron domains with no lone pairs and from three domains with zero or one lone pair?
Antwort
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°.
Karte 52
Frage
Why are metals electrically conductive as solids?
Antwort
Their delocalized electrons can move through the solid when an electric field is applied.
Karte 53
Frage
How is formal charge calculated for an atom in a Lewis diagram?
Antwort
Formal charge = valence electrons − nonbonding electrons − half the bonding electrons.
Karte 54
Frage
Why can't electronegativity difference alone classify a bond as ionic or covalent?
Antwort
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.
Karte 55
Frage
Which shapes and bond-angle trends arise as lone pairs replace bonds in four electron domains?
Antwort
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.
Karte 56
Frage
What feature of a potential-energy curve represents bond dissociation energy?
Antwort
The energy difference from the curve's minimum to the separated-atoms limit.
Karte 57
Frage
When does an ionic compound conduct electricity?
Antwort
When molten or dissolved so its ions can move; not as a rigid solid lattice.
Karte 58
Frage
What is a substitutional alloy?
Antwort
An alloy in which atoms of a similar size replace some host-metal atoms in the lattice.
Karte 59
Frage
How do two, three, and four electron domains map to hybridization?
Antwort
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.
Karte 60
Frage
What usually makes one resonance contributor more favorable than another?
Antwort
Smaller formal-charge magnitudes, appropriate negative charge on more electronegative atoms, and complete valence shells where applicable.
Karte 61
Frage
How many sigma and pi bonds are in single, double, and triple bonds?
Antwort
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.
Karte 62
Frage
Why is a polar covalent bond polar?
Antwort
Unequal electronegativity creates an uneven sharing of electron density and partial charges.
Karte 63
Frage
Which molecular shapes arise as lone pairs replace bonds in five electron domains?
Antwort
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.
Karte 64
Frage
How do ionic charge and ionic radius affect attraction between ions?
Antwort
Larger charge magnitudes and smaller ionic radii produce stronger attraction because the charge product increases and the ion centers are closer.
Karte 65
Frage
Why do ionic solids often have high melting points?
Antwort
Many strong Coulombic attractions throughout the lattice must be overcome to free the ions.
Karte 66
Frage
What is an interstitial alloy?
Antwort
A smaller atom occupies holes between host-metal atoms, often making lattice layers harder to slide.
Karte 67
Frage
What shape has six bonding domains and no lone pairs on the central atom?
Antwort
Octahedral.
Karte 68
Frage
Which elements commonly form incomplete octets in stable Lewis diagrams?
Antwort
Hydrogen forms a duet, and electron-deficient central atoms such as boron or beryllium can have fewer than eight electrons.
Karte 69
Frage
How do bond order and atomic size affect covalent bond length and strength?
Antwort
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.
Karte 70
Frage
What bonding model best fits a sample that is malleable and conducts as a solid?
Antwort
Metallic bonding with mobile, delocalized electrons and nondirectional attractions.
Karte 71
Frage
What shape has six electron domains, five bonds, and one lone pair?
Antwort
Square pyramidal.
Karte 72
Frage
Which lattice should have stronger attractions: MgO or NaCl, assuming similar separations?
Antwort
MgO, because the charge product for Mg²⁺ and O²⁻ is larger than for Na⁺ and Cl⁻.
Karte 73
Frage
Why are pure metals often malleable?
Antwort
Metal cores can shift while the mobile electron sea maintains nondirectional attraction instead of exposing fixed like-charge planes.
Karte 74
Frage
What is the best Lewis structure for CO₂?
Antwort
O=C=O, with two lone pairs on each oxygen and no formal charges.
Karte 75
Frage
What shape has six electron domains, four bonds, and two opposite lone pairs?
Antwort
Square planar.
Karte 76
Frage
What limitation does an odd total number of valence electrons create for a Lewis diagram?
Antwort
At least one electron must remain unpaired, so not every atom can have a complete paired-electron octet.
Karte 77
Frage
What does a higher bond order do to a bond's potential-energy curve?
Antwort
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.
Karte 78
Frage
When can a carbon–carbon double bond produce geometric isomers?
Antwort
When each carbon has two different substituents. The pi bond restricts rotation, so distinct spatial arrangements can persist.
Karte 79
Frage
When may a third-period central atom exceed an octet in a Lewis diagram?
Antwort
When the valid electron count and lower formal charges favor an expanded valence shell, as in species such as SF₆.
Karte 80
Frage
How do you decide whether a molecule with polar bonds is polar overall?
Antwort
Add the bond-dipole vectors using the molecular shape; symmetry may cancel them, while an asymmetric arrangement leaves a net dipole.
Karte 81
Frage
Which interparticle forces act between all atoms and molecules?
Antwort
London dispersion forces, caused by temporary and induced dipoles.
Karte 82
Frage
What four broad solid types does this deck compare?
Antwort
Ionic, metallic, molecular, and covalent-network solids.
Karte 83
Frage
How do gas particles differ from liquid particles?
Antwort
Gas particles are much farther apart and move independently; liquid particles stay close but can move past one another.
Karte 84
Frage
What relationship connects pressure, volume, amount, and temperature for an ideal gas?
Antwort
PV = nRT, with absolute temperature in kelvins and units consistent with R.
Karte 85
Frage
What does temperature measure in kinetic molecular theory?
Antwort
The particles' average translational kinetic energy.
Karte 86
Frage
What two ideal-gas assumptions fail most clearly for real gases?
Antwort
Particles have nonzero volume and experience intermolecular attractions.
Karte 87
Frage
How is molarity defined?
Antwort
Moles of solute per liter of solution: M = n/V.
Karte 88
Frage
What must a correct particulate diagram of NaCl(aq) show?
Antwort
Separated Na⁺ and Cl⁻ ions in a 1:1 ratio, each surrounded by oriented water molecules.
Karte 89
Frage
Which separation method removes an insoluble solid from a liquid?
Antwort
Filtration: the solid stays as residue while the liquid passes as filtrate.
Karte 90
Frage
What does “like dissolves like” mean at the particle level?
Antwort
A solute tends to dissolve when new solute–solvent attractions can compete with the attractions disrupted in the pure substances.
Karte 91
Frage
What happens when matter absorbs electromagnetic radiation?
Antwort
Its particles move to an allowed higher-energy state when the photon energy matches the energy gap.
Karte 92
Frage
Which equations connect photon energy, frequency, and wavelength?
Antwort
E = hν and c = λν.
Karte 93
Frage
What is the Beer–Lambert law?
Antwort
A = εbc: absorbance equals molar absorptivity at the chosen wavelength times path length times concentration.
Karte 94
Frage
What molecular features generally strengthen London dispersion forces?
Antwort
More electrons and a more polarizable cloud strengthen temporary dipoles; greater contact area and accessible π-electron density can also strengthen the attraction.
Karte 95
Frage
Why do molecular solids usually have low melting points and fail to conduct electricity?
Antwort
Distinct molecules are held together by relatively weak intermolecular forces, while their valence electrons stay localized in bonds and lone pairs.
Karte 96
Frage
How do particles move in a solid?
Antwort
They vibrate about fixed positions and do not translate past one another.
Karte 97
Frage
What graph shapes connect V or P with T(K) or n for an ideal gas?
Antwort
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.
Karte 98
Frage
At the same temperature, which gas has the greater average molecular speed: He or Xe?
Antwort
He. Both have the same average kinetic energy, but KE = ½mv² means the lower-mass particles move faster.
Karte 99
Frage
Why do real gases deviate more at high pressure?
Antwort
Particles are crowded, so their own volume is no longer negligible compared with the container volume.
Karte 100
Frage
Which relationship describes dilution when solute amount is conserved?
Antwort
M₁V₁ = M₂V₂.
Karte 101
Frage
Why does an aqueous ionic solution conduct electricity?
Antwort
Dissolved ions are mobile and carry charge through the solution.
Karte 102
Frage
Which property lets simple distillation separate two liquids?
Antwort
A sufficient difference in volatility or boiling point, so the vapor is enriched in the more volatile component.
Karte 103
Frage
Why are many ionic compounds soluble in water but poorly soluble in a nonpolar solvent?
Antwort
Water can form strong ion–dipole attractions that stabilize separated ions; a nonpolar solvent cannot provide comparable attractions.
Karte 104
Frage
Which molecular transition is commonly associated with microwave absorption?
Antwort
A transition between quantized rotational energy levels.
Karte 105
Frage
What frequency corresponds to a 600. nm photon?
Antwort
5.00 × 10^14 s^-1. Use ν = c/λ with 600. nm = 6.00 × 10^-7 m.
Karte 106
Frage
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?
Antwort
0.40. Use A = εbc.
Karte 107
Frage
What conditions allow hydrogen bonding between two molecules?
Antwort
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.
Karte 108
Frage
Why are covalent-network solids often very hard with high melting points?
Antwort
A continuous network of strong covalent bonds must be disrupted to deform or melt the solid.
Karte 109
Frage
Why do a substance's solid and liquid phases usually have similar molar volumes?
Antwort
Their particles remain in close contact in both phases, even though liquid particles can move past one another.
Karte 110
Frage
How is a gas mixture's total pressure related to its component pressures?
Antwort
Ptotal = ΣPi; each partial pressure is the pressure that component would exert alone in the same volume and temperature.
Karte 111
Frage
What microscopic events create gas pressure?
Antwort
Gas particles collide with container walls and transfer momentum.
Karte 112
Frage
Why do intermolecular attractions matter more for gases at low temperature?
Antwort
Particles move more slowly, so attractions can alter their paths and promote condensation.
Karte 113
Frage
What is the final concentration after 50.0 mL of 2.00 M solution is diluted to 200.0 mL?
Antwort
0.500 M. Use M₂ = M₁V₁/V₂.
Karte 114
Frage
What must a particulate representation of a solution communicate?
Antwort
The relative concentrations of its components and the particle-level interactions among those components.
Karte 115
Frage
What causes components to separate in chromatography?
Antwort
They differ in attraction to the stationary phase and the mobile phase, so they travel at different rates.
Karte 116
Frage
Why are many polar molecular solutes soluble in water?
Antwort
Dipole attractions or hydrogen bonds with water can replace the solute–solute and water–water attractions disrupted during mixing.
Karte 117
Frage
Why does an atom produce discrete spectral lines?
Antwort
Its electrons can occupy only quantized energy levels, so only photons matching allowed energy differences are absorbed or emitted.
Karte 118
Frage
How does photon energy change when frequency doubles?
Antwort
It doubles because E = hν.
Karte 119
Frage
Why is a calibration curve useful in spectrophotometry?
Antwort
It relates measured absorbance to known concentrations, letting an unknown concentration be read by interpolation within the linear range.
Karte 120
Frage
How does an ion–dipole attraction form, and how does it compare with dipole–dipole attraction?
Antwort
An ion attracts the oppositely charged end of a polar molecule. Ion–dipole attractions tend to be stronger than dipole–dipole attractions.
Karte 121
Frage
Which solid type is usually both conductive and malleable?
Antwort
A metallic solid, because its delocalized electrons move and its nondirectional bonding tolerates layer shifts.
Karte 122
Frage
How does a crystalline solid differ from an amorphous solid?
Antwort
A crystalline solid has long-range repeating order; an amorphous solid lacks that long-range periodic arrangement.
Karte 123
Frage
How is a gas component's partial pressure found from mole fraction?
Antwort
Pi = XiPtotal.
Karte 124
Frage
How does heating a fixed-volume gas affect its pressure in the ideal model?
Antwort
Pressure rises because faster particles collide with the walls more forcefully and frequently.
Karte 125
Frage
Why can attractions make a real gas's measured pressure lower than the ideal prediction?
Antwort
Attractions pull approaching particles away from the walls, reducing momentum transfer during wall collisions.
Karte 126
Frage
How many moles of ions result from complete dissolution of 0.20 mol CaCl₂?
Antwort
0.60 mol ions: 0.20 mol Ca²⁺ plus 0.40 mol Cl⁻.
Karte 127
Frage
How should water orient around Cl⁻ in a particle model?
Antwort
Its partially positive hydrogen ends point toward Cl⁻.
Karte 128
Frage
Can filtration separate dissolved components of a liquid solution?
Antwort
No. Dissolved particles pass through the filter with the solvent; filtration only retains an insoluble solid.
Karte 129
Frage
Why do nonpolar molecular solutes often dissolve in nonpolar solvents?
Antwort
Both rely mainly on compatible London dispersion forces, so mixing can replace the attractions disrupted in the separate substances.
Karte 130
Frage
What does a shorter absorbed wavelength imply about an energy transition?
Antwort
A larger energy gap because E = hc/λ.
Karte 131
Frage
What is the energy of a photon with frequency 5.0 × 10^14 s^-1?
Antwort
3.3 × 10^-19 J. Multiply by Planck's constant: E = (6.626 × 10^-34 J·s)(5.0 × 10^14 s^-1).
Karte 132
Frage
How does doubling cuvette path length affect absorbance in the linear Beer–Lambert range?
Antwort
Absorbance doubles if concentration and molar absorptivity stay constant.
Karte 133
Frage
How can noncovalent interactions affect a large biomolecule?
Antwort
Attractions between molecules or between different regions of the same molecule help set its shape, which strongly affects its properties and function.
Karte 134
Frage
Why does an ionic solid usually fail to conduct as a solid?
Antwort
Its ions are fixed in lattice positions. The same substance conducts when molten or dissolved because the ions can then move.
Karte 135
Frage
Why does a gas have no definite shape or volume?
Antwort
Its widely spaced particles move constantly and experience minimal interparticle attraction, so they spread through the available container.
Karte 136
Frage
What graph shapes show the inverse pressure–volume relationship for a fixed amount of ideal gas at constant temperature?
Antwort
A plot of P against V is a decreasing curve, while P against 1/V is a straight line through the origin.
Karte 137
Frage
At the same temperature, do different ideal gases have different average kinetic energies?
Antwort
No. Average translational kinetic energy depends only on absolute temperature.
Karte 138
Frage
Under which conditions is ideal-gas behavior most accurate?
Antwort
Low pressure and high temperature, where particles are far apart and attractions matter least.
Karte 139
Frage
What particle-level feature distinguishes a solution from a heterogeneous mixture?
Antwort
A solution—whether solid, liquid, or gas—is uniform throughout; a heterogeneous mixture has regions or phases with different compositions.
Karte 140
Frage
How should water orient around Na⁺ in a particulate model?
Antwort
Its partially negative oxygen end points toward Na⁺.
Karte 141
Frage
In paper chromatography, why does one solute spot travel farther than another?
Antwort
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.
Karte 142
Frage
What energy competition helps explain whether an ionic solid dissolves?
Antwort
The energy needed to separate lattice ions competes with the energy released when ion–solvent attractions form.
Karte 143
Frage
Which molecular motions commonly absorb infrared radiation?
Antwort
Bond vibrations whose changing dipole can interact with the radiation.
Karte 144
Frage
Why must wavelength be converted to meters in c = λν when c is in m s^-1?
Antwort
Consistent units are required so meters cancel correctly and frequency comes out in s^-1.
Karte 145
Frage
How can fingerprints on a cuvette affect a visible-light absorbance reading?
Antwort
They can absorb or scatter extra light, making measured absorbance too high and the inferred concentration too high.
Karte 146
Frage
What causes and controls the strength of dipole–dipole attractions?
Antwort
Opposite partial charges on neighboring polar molecules attract. Strength increases with larger molecular dipoles and depends on how favorably the dipoles are oriented.
Karte 147
Frage
Why is graphite conductive and soft while diamond is insulating and hard?
Antwort
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.
Karte 148
Frage
Why are gases much more compressible than liquids?
Antwort
Gas particles have large empty spaces between them; liquid particles are already close together.
Karte 149
Frage
What volume does 0.500 mol CO₂ occupy at 1.00 atm and 300. K if it behaves ideally?
Antwort
12.3 L. Use V = nRT/P = (0.500 mol)(0.08206 L atm mol^-1 K^-1)(300. K)/(1.00 atm).
Karte 150
Frage
Why does a lighter gas effuse faster than a heavier gas at the same temperature?
Antwort
Its particles have a higher average speed because equal average kinetic energy is shared by less mass.
Karte 151
Frage
How does finite particle volume affect a real gas at very high pressure?
Antwort
The free volume available for particle motion is smaller than the container volume assumed by the ideal model.
Karte 152
Frage
How should 250.0 mL of 0.100 M NaCl be prepared from solid NaCl?
Antwort
Dissolve 0.0250 mol NaCl, or 1.46 g, then dilute to exactly 250.0 mL in a volumetric flask.
Karte 153
Frage
What changes in a particle diagram when a solution is diluted without losing solute?
Antwort
The solute-particle count stays constant while solvent volume and particle spacing increase.
Karte 154
Frage
Why is fractional distillation better than simple distillation for liquids with close boiling points?
Antwort
Repeated vaporization–condensation steps enrich the vapor in the more volatile component more effectively.
Karte 155
Frage
Why are oil and water usually immiscible?
Antwort
Water's strong hydrogen-bond network isn't replaced by equally strong water–oil attractions, so the substances separate into phases.
Karte 156
Frage
Which molecular transition is commonly associated with ultraviolet or visible absorption?
Antwort
A transition between electronic energy levels.
Karte 157
Frage
Which photon carries more energy, blue light or red light?
Antwort
Blue light, because it has shorter wavelength and higher frequency.
Karte 158
Frage
Why is absorbance often measured at the wavelength of maximum absorbance in Beer–Lambert analysis?
Antwort
It gives the largest concentration-sensitive signal, and the flat top near the maximum makes small wavelength-setting errors less influential.
Karte 159
Frage
What creates a dipole–induced-dipole attraction, and what controls its strength?
Antwort
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.
Karte 160
Frage
How do stronger intermolecular forces affect vapor pressure, boiling point, and melting point?
Antwort
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.
Karte 161
Frage
How do particles behave in a liquid?
Antwort
They stay in close contact while moving and colliding continuously. Temperature and interparticle attractions affect their arrangement and motion.
Karte 162
Frage
Why must Celsius temperature be converted to kelvins in gas-law calculations?
Antwort
Gas-law proportionalities require an absolute temperature scale whose zero corresponds to zero extrapolated thermal motion.
Karte 163
Frage
How does raising temperature change a Maxwell–Boltzmann speed distribution?
Antwort
The distribution broadens, its peak lowers and shifts right, and a larger fraction of particles have high speed.
Karte 164
Frage
Why does the ideal-gas model treat collisions as elastic?
Antwort
It assumes total kinetic energy is conserved in particle–particle and particle–wall collisions.
Karte 165
Frage
How many moles of solute are in 75.0 mL of a 0.400 M solution?
Antwort
0.0300 mol. Multiply 0.400 mol L^-1 by 0.0750 L.
Karte 166
Frage
For equal solution volumes drawn at the same scale, what shows which solution is more concentrated?
Antwort
The more concentrated diagram contains more solute particles in that equal volume.
Karte 167
Frage
How do differences in intermolecular attractions let distillation separate a liquid solution?
Antwort
They give the components different vapor pressures, so the vapor is enriched in the more volatile component.
Karte 168
Frage
What comparison helps predict whether two liquids will be miscible?
Antwort
Liquids with similar types and strengths of intermolecular attractions are more likely to mix uniformly.
Karte 169
Frage
How can an absorption spectrum help identify a substance?
Antwort
Its allowed energy gaps produce a characteristic pattern of absorbed wavelengths that can be compared with known spectra.
Karte 170
Frage
How does absorbing or emitting a photon change an atom's or molecule's energy?
Antwort
Absorption raises the species' energy by exactly the photon energy; emission lowers it by the same amount.
Karte 171
Frage
What macroscopic evidence can support that a chemical reaction occurred?
Antwort
Evidence can include gas formation, precipitate formation, a persistent color change, or an energy change, interpreted with particle-level changes.
Karte 172
Frage
What does a net ionic equation include?
Antwort
Only the dissolved or reacting species that undergo chemical change; spectator ions are omitted.
Karte 173
Frage
What must a correct particulate reaction diagram conserve?
Antwort
The number of atoms of every element and the total charge.
Karte 174
Frage
What distinguishes a chemical change from a physical change?
Antwort
A chemical change rearranges bonds into new substances; a physical change alters state or arrangement without changing chemical identity.
Karte 175
Frage
What does a balanced equation's coefficient ratio provide?
Antwort
The mole ratio among reacting and produced species.
Karte 176
Frage
What is the equivalence point of a titration?
Antwort
The point where titrant and analyte have reacted in the stoichiometric ratio given by the balanced equation.
Karte 177
Frage
What defines a precipitation reaction?
Antwort
Aqueous ions combine to form a sparingly soluble solid.
Karte 178
Frage
What happens in a Brønsted–Lowry acid–base reaction?
Antwort
A proton transfers from the acid (donor) to the base (acceptor). In aqueous solution, H₂O can play either role.
Karte 179
Frage
What does oxidation mean in a redox reaction?
Antwort
Loss of electrons and an increase in oxidation number.
Karte 180
Frage
What particle-level change confirms that a process is chemical?
Antwort
Atoms rearrange into new combinations, producing substances with different compositions.
Karte 181
Frage
Which ions are spectators when AgNO₃(aq) reacts with NaCl(aq)?
Antwort
Na⁺ and NO₃⁻. The net ionic reaction is Ag⁺(aq) + Cl⁻(aq) → AgCl(s).
Karte 182
Frage
How does a particulate diagram reveal the limiting reactant?
Antwort
After forming the maximum product allowed by the ratio, none of the limiting reactant remains while excess reactant particles do.
Karte 183
Frage
Is melting ice a chemical or physical change?
Antwort
A physical change. H₂O molecules remain H₂O while their arrangement and motion change.
Karte 184
Frage
How is the limiting reactant identified from given amounts?
Antwort
Convert each reactant to the same product amount using the balanced equation; the smaller product amount identifies the limiting reactant.
Karte 185
Frage
How does an endpoint differ from an equivalence point?
Antwort
The endpoint is an observed signal such as indicator color change; the equivalence point is the exact stoichiometric condition.
Karte 186
Frage
How is complete combustion of a hydrocarbon in excess oxygen classified, and what products form?
Antwort
It is a redox combustion reaction that forms CO₂ and H₂O.
Karte 187
Frage
What are the conjugate acid and conjugate base in NH₃ + H₂O ⇌ NH₄⁺ + OH⁻?
Antwort
NH₄⁺ is the conjugate acid of NH₃, and OH⁻ is the conjugate base of H₂O.
Karte 188
Frage
What does reduction mean in a redox reaction?
Antwort
Gain of electrons and a decrease in oxidation number.
Karte 189
Frage
Which common changes are physical rather than chemical?
Antwort
Phase changes and the formation or separation of mixtures are physical when each substance keeps its composition.
Karte 190
Frage
How are strong soluble electrolytes written in a complete ionic equation?
Antwort
As separated aqueous ions; solids, liquids, gases, and weak electrolytes stay intact.
Karte 191
Frage
A diagram starts with six A particles and four B₂ particles for 2A + B₂ → 2AB; what remains after completion?
Antwort
One B₂ remains. Six A consume three B₂ and form six AB.
Karte 192
Frage
Why is dissolving NaCl in water normally classified as a physical change?
Antwort
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.
Karte 193
Frage
What mass of AgCl can form from 25.0 mL of 0.200 M AgNO₃ mixed with excess Cl⁻?
Antwort
0.717 g AgCl. The 1:1 reaction gives 0.00500 mol AgCl; multiply by 143.32 g mol^-1.
Karte 194
Frage
What calculation finds unknown analyte moles at equivalence?
Antwort
Use titrant moles, n = MV, then apply the balanced-reaction mole ratio.
Karte 195
Frage
Which feature identifies an acid–base, redox, or precipitation reaction?
Antwort
Acid–base reactions transfer protons, redox reactions change oxidation numbers through electron transfer, and precipitation reactions form a sparingly soluble solid.
Karte 196
Frage
What is the net ionic equation for strong acid–strong base neutralization?
Antwort
H⁺(aq) + OH⁻(aq) → H₂O(l).
Karte 197
Frage
What is the oxidation number of sulfur in SO₄²⁻?
Antwort
+6. Four oxygens contribute -8 total, so sulfur must be +6 to give -2 overall.
Karte 198
Frage
Why can gas bubbles alone be ambiguous evidence of reaction?
Antwort
Bubbles may also come from boiling or dissolved gas escaping, so the context and particle identities must support a chemical change.
Karte 199
Frage
How is melting ice represented as a balanced physical-change equation?
Antwort
H₂O(s) → H₂O(l). The formula and atom count stay the same because only the physical state changes.
Karte 200
Frage
What does a particle diagram show when no reaction occurs after two aqueous ionic solutions mix?
Antwort
All ions remain separated and solvated, with no new bonded particles, precipitate, or gas.
Karte 201
Frage
Why is rusting iron a chemical change?
Antwort
Iron atoms form new iron-oxide substances through electron transfer and new bonding.
Karte 202
Frage
For 2H₂O₂(aq) → 2H₂O(l) + O₂(g), what volume of O₂ forms from 0.100 mol H₂O₂ at 298 K and 1.00 atm?
Antwort
1.22 L O₂. The mole ratio gives 0.0500 mol O₂, then V = nRT/P.
Karte 203
Frage
A 25.0 mL monoprotic acid sample requires 20.0 mL of 0.150 M NaOH; what is the acid concentration?
Antwort
0.120 M. At 1:1 equivalence, moles acid = 0.0200 L × 0.150 M, then divide by 0.0250 L.
Karte 204
Frage
Which salts does the minimum solubility rule in this deck treat as soluble?
Antwort
All salts containing Na⁺, K⁺, NH₄⁺, or NO₃⁻ are treated as soluble in water.
Karte 205
Frage
How are the strengths of a conjugate acid and its conjugate base related?
Antwort
A stronger acid has a weaker conjugate base, and a stronger base has a weaker conjugate acid.
Karte 206
Frage
How are oxidation and reduction half-reactions combined into one balanced equation?
Antwort
Multiply them so electrons lost equal electrons gained, add the half-reactions, then cancel electrons and any identical species on both sides.
Karte 207
Frage
How do molecular, complete ionic, and net ionic equations differ?
Antwort
Molecular equations keep compounds intact, complete ionic equations split strong soluble electrolytes, and net ionic equations remove spectators. All three conserve atoms and charge.
Karte 208
Frage
How should coefficients change particle counts in a reaction diagram?
Antwort
They set whole-particle ratios while preserving each particle's chemical formula.
Karte 209
Frage
Is separating a mixture by distillation a chemical or physical change?
Antwort
A physical change. Components change phase and location but keep their chemical identities.
Karte 210
Frage
What equation results from Cu → Cu²⁺ + 2e⁻ and Ag⁺ + e⁻ → Ag?
Antwort
Cu + 2Ag⁺ → Cu²⁺ + 2Ag. Multiply the silver half-reaction by 2 and cancel 2e⁻; both atom counts and net charge then match.
Karte 211
Frage
How is average reaction rate found from a reactant concentration?
Antwort
Use the negative concentration change divided by elapsed time, adjusted by its stoichiometric coefficient when comparing species rates.
Karte 212
Frage
What does a rate law express?
Antwort
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.
Karte 213
Frage
A plot of ln[A] versus time is linear; what is the order in A and its integrated rate law?
Antwort
First order: ln[A]t = ln[A]0 − kt, so the plot's slope is −k.
Karte 214
Frage
What is an elementary reaction?
Antwort
A single step in a mechanism whose rate law follows directly from its reactant molecularity.
Karte 215
Frage
What two collision conditions are needed for reaction?
Antwort
Sufficient collision energy and a productive molecular orientation.
Karte 216
Frage
What does activation energy represent on a reaction-energy profile?
Antwort
The energy difference from the reactants to the transition state. The reaction coordinate tracks the step's structural progress, not elapsed time.
Karte 217
Frage
What must the elementary steps of a valid mechanism do when added?
Antwort
Cancel intermediates and reproduce the overall balanced reaction.
Karte 218
Frage
How is a proposed mechanism tested against kinetics?
Antwort
Its derived rate law must agree with the experimentally measured rate law.
Karte 219
Frage
What does a pre-equilibrium approximation assume?
Antwort
A fast reversible step reaches equilibrium before a later slow step consumes its intermediate.
Karte 220
Frage
What does each peak on a multistep energy profile represent?
Antwort
A transition state for one elementary step.
Karte 221
Frage
How does a catalyst increase reaction rate?
Antwort
It provides an alternate mechanism with a lower activation-energy pathway.
Karte 222
Frage
Why does crushing a solid reactant usually increase its reaction rate?
Antwort
Crushing increases exposed surface area, so more reactant particles can collide with the other reactant each second.
Karte 223
Frage
How is reaction order found from initial-rate data?
Antwort
Compare trials where one reactant concentration changes while the others stay constant, then match the rate factor to the concentration factor.
Karte 224
Frage
A plot of [A] versus time is linear; what is the order in A and its integrated rate law?
Antwort
Zero order: [A]t = [A]0 − kt, so the plot's slope is −k.
Karte 225
Frage
What is the rate law for the elementary step 2A + B → products?
Antwort
rate = k[A]²[B]. This inference is valid because the step is elementary.
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Karte 226
Frage
How does raising temperature change a Maxwell–Boltzmann energy distribution and reaction rate?
Antwort
The distribution shifts and broadens toward higher energies, so a larger fraction of collisions exceeds the activation-energy threshold and can react.
Karte 227
Frage
How is ΔH read from a reaction-energy profile?
Antwort
ΔH = energy of products − energy of reactants.
Karte 228
Frage
What is a reaction intermediate?
Antwort
A species formed in one mechanism step and consumed in a later step, so it cancels from the overall equation.
Karte 229
Frage
Why can't overall reaction coefficients usually supply rate-law exponents?
Antwort
The overall equation hides the mechanism; exponents come from experiment unless the reaction is a stated elementary step.
Karte 230
Frage
How does pre-equilibrium remove an intermediate from a rate law?
Antwort
Use the fast-step equilibrium relation to express the intermediate concentration in terms of stable reactants.
Karte 231
Frage
What does each valley between peaks represent on a multistep profile?
Antwort
A reaction intermediate.
Karte 232
Frage
Does a catalyst change ΔH or the equilibrium constant?
Antwort
No. It changes the pathway and rates, not reactant/product energies or the equilibrium composition.
Karte 233
Frage
For 2A → B, how are disappearance of A and appearance of B related?
Antwort
Reaction rate = -(1/2)Δ[A]/Δt = Δ[B]/Δt.
Karte 234
Frage
How do the units of k depend on a rate law's overall order?
Antwort
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.
Karte 235
Frage
A plot of 1/[A] versus time is linear; what is the order in A and its integrated rate law?
Antwort
Second order: 1/[A]t = 1/[A]0 + kt, so the plot's slope is +k.
Karte 236
Frage
What is molecularity?
Antwort
The number of reacting particles in an elementary step, such as unimolecular or bimolecular.
Karte 237
Frage
How does raising temperature affect k in the qualitative Arrhenius model?
Antwort
k increases, often sharply, because a larger fraction of collisions can reach the transition state. Arrhenius-equation calculations are outside this deck’s scope.
Karte 238
Frage
A reactant falls from 0.80 M to 0.50 M in 30. s; what is its average disappearance rate to two significant figures?
Antwort
0.010 M s^-1. Use -(0.50 − 0.80) M ÷ 30. s.
Karte 239
Frage
How does a catalyst differ from an intermediate in a mechanism?
Antwort
A catalyst is consumed early and regenerated later; an intermediate is formed early and consumed later.
Karte 240
Frage
For 2NO₂ → NO₃ + NO (slow), followed by NO₃ + CO → NO₂ + CO₂ (fast), what rate law is predicted?
Antwort
rate = k[NO₂]². The first step is elementary and rate-limiting, so its molecularity sets the observed rate law.
Karte 241
Frage
On a multistep reaction-energy profile, which feature often identifies the rate-determining step?
Antwort
The step with the largest activation barrier measured from its preceding valley to its peak.
Karte 242
Frage
If changing [B] leaves rate unchanged, what is the order in B?
Antwort
Zero order, so [B]^0 = 1 in the measured rate law.
Karte 243
Frage
What mechanism changes can binding, acid–base, or surface catalysis introduce?
Antwort
They can orient reactants, lower activation barriers, or create new bound, protonated, or deprotonated intermediates and elementary steps; the catalyst is regenerated.
Karte 244
Frage
What is special about a first-order reaction's half-life?
Antwort
It is constant and independent of starting concentration: t1/2 = ln 2/k. Radioactive decay is a common first-order example.
Karte 245
Frage
Why is a termolecular elementary collision uncommon?
Antwort
Three particles must collide simultaneously with suitable energy and orientation, which is much less probable than one- or two-particle events.
Karte 246
Frage
On a reaction-energy profile, how are reverse activation energy, forward activation energy, and ΔH related?
Antwort
Ea,reverse = Ea,forward − ΔH. The reverse barrier is measured from products to the same transition state.
Karte 247
Frage
Why can correct orientation matter even above the activation energy?
Antwort
The colliding reactive sites must align so old bonds can break and new bonds can form along the reaction pathway.
Karte 248
Frage
How does detecting a proposed reaction intermediate affect a mechanism claim?
Antwort
It supports a mechanism that contains that intermediate, but it doesn't prove that mechanism is unique.
Karte 249
Frage
For 2NO ⇌ N₂O₂ (fast equilibrium), followed by N₂O₂ + O₂ → 2NO₂ (slow), what observed rate law results?
Antwort
rate = kobs[NO]²[O₂]. Start with rate = k₂[N₂O₂][O₂], use [N₂O₂] = K[NO]² from the fast equilibrium, then substitute.
Karte 250
Frage
What does the highest point of a one-step energy profile represent?
Antwort
The transition state, an unstable arrangement at the top of the activation barrier.
Karte 251
Frage
What sign does q have for an endothermic system?
Antwort
Positive, because the system absorbs heat from the surroundings.
Karte 252
Frage
How does an exothermic reaction appear on an enthalpy diagram?
Antwort
Products lie below reactants, so ΔH is negative.
Karte 253
Frage
What condition defines thermal equilibrium?
Antwort
Objects in contact have the same temperature, so there is no net heat transfer.
Karte 254
Frage
What equations relate heat capacity and temperature change to heat transfer?
Antwort
Use q = mcΔT with specific heat capacity, or q = nCₘΔT with molar heat capacity.
Karte 255
Frage
Why is temperature constant during a phase-change plateau?
Antwort
Added or removed energy changes interparticle potential energy instead of average kinetic energy.
Karte 256
Frage
What does ΔHrxn describe?
Antwort
The heat absorbed or released at constant pressure for the reaction exactly as written under the stated conditions.
Karte 257
Frage
How is reaction enthalpy estimated from average bond enthalpies?
Antwort
ΔHrxn ≈ Σ(bonds broken) − Σ(bonds formed).
Karte 258
Frage
What is the standard enthalpy of formation of an element in its standard state?
Antwort
Zero by definition.
Karte 259
Frage
In a Hess’s law calculation, how should a step change when the target needs twice its reverse?
Antwort
Reverse the equation, double every coefficient, and multiply its ΔH by -2.
Karte 260
Frage
How can energy cross a system boundary during a process?
Antwort
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.
Karte 261
Frage
How does an endothermic reaction appear on an enthalpy diagram?
Antwort
Products lie above reactants, so ΔH is positive.
Karte 262
Frage
How are heat gained by a system and heat lost by its surroundings related in an isolated setup?
Antwort
qsystem = -qsurroundings.
Karte 263
Frage
In coffee-cup calorimetry, how is reaction heat related to solution heat?
Antwort
qrxn = -qsolution when calorimeter heat is negligible and pressure is constant.
Karte 264
Frage
What heat is required to melt n moles at the melting point?
Antwort
q = nΔHfus.
Karte 265
Frage
How does reversing a reaction change ΔH?
Antwort
It reverses the sign of ΔH.
Karte 266
Frage
Why is breaking a bond endothermic?
Antwort
Energy must be supplied to separate atoms against their bonding attraction.
Karte 267
Frage
How is ΔH°rxn calculated from standard enthalpies of formation?
Antwort
ΣνΔHf°(products) − ΣνΔHf°(reactants).
Karte 268
Frage
How does multiplying an equation by 3 affect its ΔH?
Antwort
Multiply ΔH by 3 because enthalpy change scales with reaction amount.
Karte 269
Frage
Why can an exothermic dissolution warm the solution?
Antwort
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.
Karte 270
Frage
Does an energy diagram's activation barrier determine ΔH?
Antwort
No. ΔH depends on reactant and product energy levels, while the barrier controls kinetics.
Karte 271
Frage
Why does heat flow from a warmer object to a cooler object?
Antwort
Energy transfers through collisions until their average kinetic energies, and therefore temperatures, equalize.
Karte 272
Frage
How much heat warms 100.0 g of water by 5.0°C?
Antwort
2.1 kJ. Use q = (100.0 g)(4.184 J g^-1 °C^-1)(5.0°C).
Karte 273
Frage
How are the molar enthalpies of a phase change and its reverse related?
Antwort
They have equal magnitudes and opposite signs, such as ΔHcond = -ΔHvap and ΔHfreeze = -ΔHfus.
Karte 274
Frage
How does doubling every coefficient in a thermochemical equation affect ΔH?
Antwort
It doubles ΔH.
Karte 275
Frage
Why is forming a bond exothermic?
Antwort
Atoms move to a lower-potential-energy bonded arrangement and release energy.
Karte 276
Frage
What formation equation defines ΔHf° for CO₂(g)?
Antwort
C(s, graphite) + O₂(g) → CO₂(g), forming exactly one mole from elements in standard states.
Karte 277
Frage
What should happen to intermediate species when equations in a Hess’s law calculation are added?
Antwort
They cancel, leaving the target overall reaction.
Karte 278
Frage
If the surroundings warm during a process, what is the likely sign of qsystem?
Antwort
Negative; the system likely released heat to the surroundings.
Karte 279
Frage
For a profile with reactants at 40 kJ and products at 10 kJ, what is ΔH?
Antwort
-30 kJ for the reaction as drawn.
Karte 280
Frage
Assuming no phase change, what determines the final temperature when two substances exchange heat in an insulated container?
Antwort
Energy conservation: q_warm + q_cool = 0. Use each substance's mass, heat capacity, and initial temperature to solve for the common final temperature.
Karte 281
Frage
How would heat loss to the room affect an exothermic calorimetry result?
Antwort
The observed temperature rise is too small, so the calculated magnitude of released heat is too low.
Karte 282
Frage
What heat expression covers warming a liquid without a phase change?
Antwort
q = mcΔT, not nΔHphase.
Karte 283
Frage
If forming 1 mol of product has ΔH = -50 kJ mol^-1, what is q when 2 mol forms?
Antwort
-100 kJ. Use q = nΔH = (2 mol)(-50 kJ mol^-1).
Karte 284
Frage
Breaking reactant bonds requires 500 kJ, and forming product bonds releases 650 kJ; what is the estimated ΔH?
Antwort
-150 kJ, from 500 − 650.
Karte 285
Frage
For CO(g) + ½O₂(g) → CO₂(g), what is ΔH°rxn if ΔHf°[CO] = -110.5 and ΔHf°[CO₂] = -393.5 kJ mol^-1?
Antwort
-283.0 kJ. Use -393.5 - [-110.5 + ½(0)], since ΔHf°[O₂(g)] = 0.
Karte 286
Frage
In a Hess’s law calculation, two valid steps have ΔH values +25 kJ and -60 kJ; what is the combined ΔH?
Antwort
-35 kJ, provided the equations add to the target reaction.
Karte 287
Frage
Why is “bonds breaking releases energy” incorrect?
Antwort
Bond breaking absorbs energy; the overall reaction releases energy only when forming new bonds releases more than breaking old bonds requires.
Karte 288
Frage
How would melting appear on an energy diagram?
Antwort
The liquid lies above the solid, so ΔHfus is positive; the diagram represents a physical, endothermic change.
Karte 289
Frage
Can two objects at the same temperature exchange energy microscopically?
Antwort
Yes, but their energy transfers balance, so there is no net heat flow.
Karte 290
Frage
Why must the calorimeter's heat capacity be included when it isn't negligible?
Antwort
The apparatus can absorb or release heat, so include q_cal = C_calΔT in the energy balance: q_process + q_solution + q_cal = 0.
Karte 291
Frage
What makes chemical equilibrium dynamic?
Antwort
Forward and reverse reactions continue at equal rates even though macroscopic concentrations stay constant.
Karte 292
Frage
For aA + bB ⇌ cC, what is the concentration-form expression for Q?
Antwort
Q = [C]^c / ([A]^a[B]^b), using current rather than necessarily equilibrium concentrations.
Karte 293
Frage
What does K much greater than 1 indicate?
Antwort
Products predominate at equilibrium, though K says nothing about reaction speed.
Karte 294
Frage
How does reversing a reaction change its equilibrium constant?
Antwort
K becomes 1/K.
Karte 295
Frage
Can a reversible system reach equilibrium when it starts with only products?
Antwort
Yes, if the reverse reaction is possible. The equilibrium composition depends on temperature, initial amounts, and volume or pressure.
Karte 296
Frage
How do Q and K predict reaction direction?
Antwort
Q < K shifts forward, Q > K shifts reverse, and Q = K means equilibrium.
Karte 297
Frage
Which species are omitted from a heterogeneous equilibrium expression?
Antwort
Pure solids and pure liquids because their activities are effectively constant.
Karte 298
Frage
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?
Antwort
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.
Karte 299
Frage
What does a flat concentration-time graph mean at equilibrium?
Antwort
Each concentration is constant, not necessarily equal to the others.
Karte 300
Frage
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?
Antwort
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.
Karte 301
Frage
What can Ksp tell you about a salt's solubility, and when can two Ksp values be compared directly?
Antwort
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.
Karte 302
Frage
What is the common-ion effect on solubility?
Antwort
Adding an ion already in the dissolution equilibrium usually decreases the solid's molar solubility.
Karte 303
Frage
How does uniform dilution shift an aqueous equilibrium based on the stoichiometric powers in Q?
Antwort
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.
Karte 304
Frage
What happens if a reversible reaction starts with reactants only?
Antwort
The forward rate is initially largest; products form, the reverse rate grows, and the rates eventually become equal.
Karte 305
Frage
What is the purpose of an ICE table?
Antwort
To organize initial, change, and equilibrium concentrations using reaction stoichiometry.
Karte 306
Frage
Can a reaction with a very large K be slow?
Antwort
Yes. K describes thermodynamic equilibrium position, while rate depends on kinetics and activation energy.
Karte 307
Frage
What happens to Q immediately after product concentration increases?
Antwort
Q increases; if it rises above K, the reaction shifts toward reactants.
Karte 308
Frage
How does multiplying every reaction coefficient by 2 affect K?
Antwort
The new equilibrium constant is K².
Karte 309
Frage
For A ⇌ B, Kc = 4.0 and initially [A] = 1.0 M and [B] = 0, what are the equilibrium concentrations?
Antwort
[A] = 0.20 M and [B] = 0.80 M. Let x form: Kc = x/(1.0 − x) = 4.0, so x = 0.80 M.
Karte 310
Frage
What macroscopic properties stay constant at equilibrium?
Antwort
Properties such as concentration, color, and pressure remain constant when external conditions are fixed.
Karte 311
Frage
How does decreasing volume shift a gaseous equilibrium?
Antwort
Toward the side with fewer moles of gas, if the two sides have different gaseous mole counts.
Karte 312
Frage
For N₂ + 3H₂ ⇌ 2NH₃, what is Kc?
Antwort
Kc = [NH₃]² / ([N₂][H₂]³).
Karte 313
Frage
For CaF₂(s) ⇌ Ca²⁺ + 2F⁻, how is Ksp written in terms of molar solubility s in pure water?
Antwort
Ksp = s(2s)² = 4s³ because [Ca²⁺] = s and [F⁻] = 2s.
Karte 314
Frage
What does K much less than 1 indicate?
Antwort
Reactants predominate at equilibrium.
Karte 315
Frage
How does decreasing a dissolved product's concentration or a gaseous product's partial pressure affect equilibrium when other Q terms are initially unchanged?
Antwort
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.
Karte 316
Frage
Does equilibrium mean the reaction has stopped?
Antwort
No. Both directions continue, but equal rates produce no net macroscopic change.
Karte 317
Frage
Why does adding NaF reduce CaF₂ solubility?
Antwort
The added F⁻ raises Qsp, shifting the dissolution equilibrium toward solid CaF₂.
Karte 318
Frage
For N₂ + 3H₂ ⇌ 2NH₃, what is Kp when P_N₂ = 0.50 atm, P_H₂ = 1.50 atm, and P_NH₃ = 0.25 atm?
Antwort
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.
Karte 319
Frage
What happens to Q when a gaseous equilibrium mixture is compressed at constant temperature if products have fewer gas moles?
Antwort
Q falls relative to K, so the reaction shifts toward products.
Karte 320
Frage
How do K and Q transform when a reaction is reversed, its coefficients are multiplied, or reactions are added?
Antwort
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.
Karte 321
Frage
When is the small-x approximation acceptable?
Antwort
When x is small relative to the initial concentration and the final result confirms the neglected change is suitably small.
Karte 322
Frage
What graph feature shows a disturbance followed by re-equilibration?
Antwort
A sudden or gradual concentration change followed by new constant plateaus while rates return to equality.
Karte 323
Frage
If Q = 0.20 and K = 5.0, which direction is favored next?
Antwort
Forward, because Q < K.
Karte 324
Frage
At equilibrium, are reactant and product concentrations equal?
Antwort
Not necessarily. They are constant, while forward and reverse rates are equal.
Karte 325
Frage
CaF₂ has Ksp = 3.2 × 10^-11 in pure water; what is its molar solubility?
Antwort
2.0 × 10^-4 M. If the molar solubility is s, then [Ca²⁺] = s, [F⁻] = 2s, and Ksp = 4s³.
Karte 326
Frage
For N₂ + 3H₂ ⇌ 2NH₃, how is Qp written?
Antwort
Qp = (P_NH₃)²/[(P_N₂)(P_H₂)³], using the current partial pressures rather than necessarily equilibrium values.
Karte 327
Frage
How does heating shift an endothermic forward reaction?
Antwort
Toward products, and K increases because temperature changes the equilibrium constant.
Karte 328
Frage
Why do both forward and reverse rates change as equilibrium is approached?
Antwort
As reactant and product concentrations change, the collision frequencies for the two directions change until their rates match.
Karte 329
Frage
CaF₂ has Ksp = 3.2 × 10^-11. What is its molar solubility in 0.10 M NaF?
Antwort
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.
Karte 330
Frage
What concentration data must be used to calculate Kc?
Antwort
Equilibrium concentrations, each raised to its stoichiometric coefficient and excluding pure solids and liquids.
Karte 331
Frage
What is a Brønsted–Lowry acid?
Antwort
A proton donor.
Karte 332
Frage
How is pH defined?
Antwort
pH = -log[H₃O⁺].
Karte 333
Frage
What is Ka for HA + H₂O ⇌ H₃O⁺ + A⁻?
Antwort
Ka = [H₃O⁺][A⁻]/[HA].
Karte 334
Frage
How does stabilizing a base affect its basicity and the strength of its conjugate acid?
Antwort
It makes the base weaker and its conjugate acid stronger. A more stable base is less willing to accept H⁺.
Karte 335
Frage
What is a Brønsted–Lowry base?
Antwort
A proton acceptor.
Karte 336
Frage
At 25°C, what are Kw and the relationship between pH and pOH?
Antwort
Kw = [H₃O⁺][OH⁻] = 1.0 × 10^-14. Taking negative logarithms gives pH + pOH = 14.00.
Karte 337
Frage
What is Kb for B + H₂O ⇌ BH⁺ + OH⁻?
Antwort
Kb = [BH⁺][OH⁻]/[B].
Karte 338
Frage
Why can lowering pH increase the solubility of a salt containing a basic anion?
Antwort
H₃O⁺ consumes the anion, pulling the dissolution equilibrium toward more dissolved ions.
Karte 339
Frage
What are conjugate acid–base pairs?
Antwort
Species that differ by exactly one proton.
Karte 340
Frage
What is the pH of 1.0 × 10^-3 M HCl?
Antwort
3.00, assuming complete dissociation and negligible water contribution.
Karte 341
Frage
How are pKa and pKb defined?
Antwort
pKa = -log Ka, and pKb = -log Kb.
Karte 342
Frage
Why does acid strength increase across a row of comparable hydrides?
Antwort
Increasing electronegativity stabilizes the conjugate base and polarizes the H–A bond.
Karte 343
Frage
What is an amphiprotic species?
Antwort
A species that can donate or accept a proton, such as HCO₃⁻.
Karte 344
Frage
What amounts remain after a limited amount of strong base partially neutralizes weak acid HA?
Antwort
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.
Karte 345
Frage
How are Ka, Kb, pKa, and pKb related for a conjugate pair at 25°C?
Antwort
KaKb = Kw = 1.0 × 10^-14, and pKa + pKb = pKw = 14.00.
Karte 346
Frage
When does pH have little effect on a salt's solubility?
Antwort
When neither dissolved ion reacts appreciably with H₃O⁺ or OH⁻.
Karte 347
Frage
How does H₂O act in HCl + H₂O → H₃O⁺ + Cl⁻ and in NH₃ + H₂O ⇌ NH₄⁺ + OH⁻?
Antwort
It acts as a base in the first reaction by accepting H⁺, and as an acid in the second by donating H⁺.
Karte 348
Frage
After mixing weak base B with strong acid, what controls the final solution in the three stoichiometric regimes?
Antwort
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⁺.
Karte 349
Frage
What two components make a typical weak-acid buffer?
Antwort
A weak acid and a significant amount of its conjugate base.
Karte 350
Frage
What do the successive half-equivalence pH values approximate in a diprotic weak-acid titration?
Antwort
The first approximates pKa₁ and the second approximates pKa₂ because each conjugate pair has equal concentrations at its half-equivalence point.
Karte 351
Frage
Which acid is stronger, one with pKa 2 or pKa 5?
Antwort
The acid with pKa 2; lower pKa means larger Ka.
Karte 352
Frage
What is the Henderson–Hasselbalch equation?
Antwort
pH = pKa + log([A⁻]/[HA]).
Karte 353
Frage
Why are larger binary hydrides down a group often stronger acids?
Antwort
The H–A bond becomes weaker as the central atom grows, so proton release is easier.
Karte 354
Frage
What mainly determines buffer capacity?
Antwort
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.
Karte 355
Frage
Why does acid increase CaCO₃ solubility?
Antwort
H₃O⁺ converts CO₃²⁻ to HCO₃⁻ or carbonic acid species, reducing free carbonate and driving more CaCO₃ to dissolve.
Karte 356
Frage
What does pH < pKa imply for a weak-acid pair?
Antwort
The protonated form HA predominates over A⁻.
Karte 357
Frage
What happens when stoichiometrically equal amounts of a monoprotic weak acid and strong base are mixed?
Antwort
The weak acid is consumed to its conjugate base; at equivalence, the solution isn't a buffer containing both forms.
Karte 358
Frage
What is [H₃O⁺] when pH = 4.50?
Antwort
3.2 × 10^-5 M, from [H₃O⁺] = 10^-pH.
Karte 359
Frage
What is the pH of 0.010 M Ba(OH)₂ at 25°C?
Antwort
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.
Karte 360
Frage
How does a buffer respond to a small amount of added strong acid?
Antwort
Its conjugate base consumes H⁺, converting to the weak acid and limiting the pH change.
Karte 361
Frage
Why is the equivalence-point solution basic in a monoprotic weak-acid–strong-base titration?
Antwort
The conjugate base produced at equivalence reacts with water to form OH⁻, so the pH is above neutral—above 7.00 at 25°C.
Karte 362
Frage
How is percent ionization calculated for a weak acid or weak base?
Antwort
For HA, use ([H₃O⁺]equilibrium ÷ [HA]initial) × 100%. For B, use ([BH⁺]equilibrium ÷ [B]initial) × 100%, under the usual monoprotic setup.
Karte 363
Frage
When is Henderson–Hasselbalch useful for an initial buffer-pH calculation?
Antwort
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.
Karte 364
Frage
Why does adding oxygen atoms usually strengthen oxyacids with the same central atom?
Antwort
Extra oxygens withdraw electron density and delocalize negative charge in the conjugate base.
Karte 365
Frage
A prepared buffer is accidentally diluted to twice its intended volume; what happens to its pH and capacity?
Antwort
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.
Karte 366
Frage
How does adding OH⁻ affect Mg(OH)₂ solubility?
Antwort
It decreases solubility through the common-ion effect, shifting Mg(OH)₂(s) ⇌ Mg²⁺ + 2OH⁻ toward the solid.
Karte 367
Frage
A buffer has equal [A⁻] and [HA]; what is its pH?
Antwort
pH = pKa because log(1) = 0.
Karte 368
Frage
How should a weak acid–strong base mixture be solved before equivalence?
Antwort
First use mole stoichiometry; if both HA and A⁻ remain, use the resulting buffer relation.
Karte 369
Frage
Why can pure neutral water have a pH other than 7.00?
Antwort
Kw changes with temperature. Neutrality means [H₃O⁺] = [OH⁻], while pH = 7.00 only when Kw = 1.0 × 10^-14 at 25°C.
Karte 370
Frage
25.0 mL of 0.200 M HCl is diluted to 100.0 mL; what is the pH?
Antwort
1.301. Dilution gives [H₃O⁺] = (0.200 M)(25.0 mL)/(100.0 mL) = 0.0500 M, so pH = -log(0.0500).
Karte 371
Frage
How does a buffer respond to a small amount of added strong base?
Antwort
The weak acid consumes OH⁻, forming conjugate base and water.
Karte 372
Frage
How do you find the final pH after mixing a strong acid and strong base at 25°C?
Antwort
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.
Karte 373
Frage
What distinguishes acid strength from acid concentration?
Antwort
Strength is the equilibrium tendency to donate H⁺, reflected by Ka or pKa; concentration is the amount of acid per solution volume.
Karte 374
Frage
If [A⁻]/[HA] = 10, how does pH compare with pKa?
Antwort
pH = pKa + 1 because log 10 = 1.
Karte 375
Frage
Which conjugate base is more stable, one with localized or resonance-delocalized charge?
Antwort
The resonance-delocalized conjugate base, which generally corresponds to the stronger acid.
Karte 376
Frage
Which 1.0 L buffer has greater capacity: 1.0 mol each of HA/A⁻ or 0.10 mol each at the same ratio?
Antwort
The 1.0 mol pair; both have the same initial pH, but the larger amounts neutralize more added acid or base.
Karte 377
Frage
For BHX(s) ⇌ BH⁺ + X⁻, why can raising pH increase the salt's solubility?
Antwort
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.
Karte 378
Frage
What does pH > pKa imply for a weak-acid pair?
Antwort
The deprotonated form A⁻ predominates over HA.
Karte 379
Frage
For HA + B ⇌ A⁻ + BH⁺, which side is favored when pKa(HA) = 4 and pKa(BH⁺) = 9?
Antwort
Products are favored. Proton transfer moves toward the weaker acid–base pair, and K ≈ 10^(9 − 4) = 10^5.
Karte 380
Frage
What is the pOH when [OH⁻] = 2.5 × 10^-4 M?
Antwort
3.60, from -log(2.5 × 10^-4).
Karte 381
Frage
What is the pH of 0.100 M HA when Ka = 1.0 × 10^-5?
Antwort
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.
Karte 382
Frage
Why does a buffer fail after too much strong acid is added?
Antwort
Its conjugate base is depleted, so added H⁺ is no longer consumed effectively.
Karte 383
Frage
What do two clear equivalence regions on an acid titration curve suggest?
Antwort
At least two distinguishable titratable protons; on a clean ideal curve with exactly two equivalence regions, this is consistent with a diprotic acid.
Karte 384
Frage
A buffer has pKa 4.8 and [A⁻]/[HA] = 0.10; what is pH?
Antwort
3.8, from 4.8 + log(0.10).
Karte 385
Frage
Why is HCl stronger than HF in water despite F being more electronegative?
Antwort
The H–F bond is much stronger; bond strength dominates this down-group binary-acid comparison.
Karte 386
Frage
Why does percent ionization increase when a weak acid is diluted?
Antwort
Dilution shifts ionization toward more particles, so a larger fraction ionizes even though [H₃O⁺] decreases.
Karte 387
Frage
A buffer contains more HA than A⁻. Which addition can it neutralize in greater amount: strong acid or strong base?
Antwort
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.
Karte 388
Frage
Why can removing a basic anion increase a salt's molar solubility without changing Ksp?
Antwort
The equilibrium shifts to replace the consumed ion; Ksp remains fixed at the same temperature.
Karte 389
Frage
Why can an acid–base indicator change color as pH changes?
Antwort
Its protonated and deprotonated forms have different colors or other observable properties, and their relative amounts change with pH.
Karte 390
Frage
What buffer results from mixing 1.0 mol HA with 0.40 mol OH⁻?
Antwort
0.60 mol HA and 0.40 mol A⁻ remain, forming a buffer before any equilibrium calculation.
Karte 391
Frage
What is the pH of 0.200 M weak base B when Kb = 2.0 × 10^-5 at 25°C?
Antwort
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.
Karte 392
Frage
Why does a weak acid alone not make an effective buffer?
Antwort
It lacks a substantial conjugate-base reserve to consume added strong acid.
Karte 393
Frage
What controls pH after excess strong base passes equivalence?
Antwort
The concentration of excess OH⁻ after accounting for reaction stoichiometry and total volume.
Karte 394
Frage
How should an indicator be chosen for a titration?
Antwort
Its color-change range should fall within the steep pH change near the equivalence point.
Karte 395
Frage
How can a measured pH and known pKa give a conjugate-base/acid ratio?
Antwort
Rearrange Henderson–Hasselbalch: [A⁻]/[HA] = 10^(pH − pKa).
Karte 396
Frage
Can a weak base and its conjugate acid form a buffer?
Antwort
Yes, when both are present in significant amounts.
Karte 397
Frage
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?
Antwort
The concentrated buffer changes pH less because it has greater capacity.
Karte 398
Frage
How does equivalence-point pH compare for strong acid–strong base, weak acid–strong base, and weak base–strong acid titrations at 25°C?
Antwort
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.
Karte 399
Frage
Why should mole ratios replace concentration ratios after mixing buffer solutions?
Antwort
Both components share the same final volume, so that volume cancels in [A⁻]/[HA].
Karte 400
Frage
How does adding a little strong acid change a buffer's conjugate-base and conjugate-acid amounts?
Antwort
The conjugate base decreases and its conjugate acid increases by the amount of strong acid consumed.
Karte 401
Frage
What does entropy measure qualitatively?
Antwort
The dispersal of matter and energy among available microstates.
Karte 402
Frage
How is standard reaction entropy calculated?
Antwort
ΔS°rxn = ΣνS°(products) − ΣνS°(reactants).
Karte 403
Frage
What equation gives ΔG° from ΔH° and ΔS°, and what standard states do the degree symbols assume?
Antwort
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.
Karte 404
Frage
Does thermodynamic favorability guarantee a fast reaction?
Antwort
No. A favorable reaction can be slow when its activation barrier is large.
Karte 405
Frage
What is ΔG at equilibrium?
Antwort
Zero under the current conditions because there is no net driving force.
Karte 406
Frage
Why can an endothermic dissolution still be thermodynamically favorable?
Antwort
A sufficiently positive entropy change can make TΔS exceed positive ΔH, giving negative ΔG.
Karte 407
Frage
How can an unfavorable reaction be driven by a favorable one?
Antwort
Couple them so their equations and ΔG values add to a negative overall ΔG.
Karte 408
Frage
Where does oxidation occur in every electrochemical cell?
Antwort
At the anode.
Karte 409
Frage
How are standard cell potential and standard free energy related?
Antwort
ΔG° = -nFE°cell.
Karte 410
Frage
What equation gives cell potential under nonstandard conditions?
Antwort
E = E° − (RT/nF) ln Q. When Q = 1, ln Q = 0, so E = E°.
Karte 411
Frage
How is electrical charge related to current and time?
Antwort
q = It.
Karte 412
Frage
Which phase has greater molar entropy, liquid water or ice at the same temperature?
Antwort
Liquid water because its molecules have more accessible arrangements and motion.
Karte 413
Frage
Do elements in their standard states have zero standard molar entropy?
Antwort
No. Their ΔHf° is zero, but their absolute S° values are positive above 0 K.
Karte 414
Frage
How do the four ΔH° and ΔS° sign combinations determine thermodynamic favorability across temperature?
Antwort
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.
Karte 415
Frage
What does it indicate when a thermodynamically favored process does not occur at a measurable rate?
Antwort
It is under kinetic control, commonly because of a high activation energy; no measurable reaction does not mean the system is at equilibrium.
Karte 416
Frage
How are ΔG° and K related?
Antwort
ΔG° = -RT ln K.
Karte 417
Frage
What two contributions compete in dissolving an ionic solid?
Antwort
Enthalpy changes from separating and solvating particles, and entropy changes from their new dispersal and solvent organization.
Karte 418
Frage
What must cancel when coupled reactions are added?
Antwort
Shared intermediates, leaving the desired net reaction.
Karte 419
Frage
Where does reduction occur in every electrochemical cell?
Antwort
At the cathode.
Karte 420
Frage
What sign of E°cell indicates a favorable standard galvanic reaction?
Antwort
Positive E°cell, corresponding to negative ΔG°.
Karte 421
Frage
If Q increases for a galvanic reaction, how does E change at fixed temperature?
Antwort
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.
Karte 422
Frage
How are moles of electrons found from charge?
Antwort
Moles e⁻ = q/F, where F ≈ 96485 C mol^-1 e⁻.
Karte 423
Frage
How does producing more gas particles usually affect system entropy?
Antwort
It increases entropy because the particles have more positional microstates.
Karte 424
Frage
Can a dissolution with negative ΔH be unfavorable?
Antwort
Yes. A sufficiently negative entropy change at the stated temperature can make ΔG positive.
Karte 425
Frage
When can a process with ΔH > 0 and ΔS > 0 become favorable?
Antwort
At sufficiently high temperature, when TΔS exceeds ΔH.
Karte 426
Frage
How does a catalyst affect ΔG?
Antwort
It does not change ΔG; it lowers the activation barrier for both directions.
Karte 427
Frage
For A → B, ΔGf°(A) = -50 kJ mol^-1 and ΔGf°(B) = -80 kJ mol^-1. What is ΔG°rxn?
Antwort
-30 kJ mol^-1. Use ΣνΔGf°(products) − ΣνΔGf°(reactants) = -80 − (-50).
Karte 428
Frage
Why can dissolving a gas in a liquid have a negative entropy change?
Antwort
Gas particles lose much of their translational freedom when confined and solvated in the liquid.
Karte 429
Frage
If coupled steps have ΔG values +20 kJ and -35 kJ, what is overall ΔG?
Antwort
-15 kJ, so the combined process is thermodynamically favorable under those conditions.
Karte 430
Frage
What role does each half-cell solution play in an electrochemical cell?
Antwort
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.
Karte 431
Frage
How is E°cell found from standard reduction potentials?
Antwort
E°cell = E°cathode − E°anode, using both tabulated values as reductions.
Karte 432
Frage
How does a cell's potential magnitude change as Q approaches or moves away from K, and what is E at equilibrium?
Antwort
|E| falls toward zero as Q approaches K and grows as the system moves farther from equilibrium. At equilibrium, Q = K and E = 0.
Karte 433
Frage
How many moles of electrons pass when 1.93 × 10^5 C flows?
Antwort
2.00 mol e⁻, from q/F.
Karte 434
Frage
How does a salt bridge maintain charge balance in a galvanic cell?
Antwort
Anions migrate toward the anode compartment and cations toward the cathode compartment, countering the net charge imbalances created by the two half-reactions.
Karte 435
Frage
Why does raising a substance's temperature generally increase its entropy?
Antwort
Energy spreads across more accessible particle energy states, increasing the number of possible microscopic arrangements.
Karte 436
Frage
When can a process with ΔH < 0 and ΔS < 0 be favorable?
Antwort
At sufficiently low temperature, where the unfavorable -TΔS term is small.
Karte 437
Frage
Why can diamond persist even though graphite is more stable at standard conditions?
Antwort
Conversion has a large activation barrier, so diamond is kinetically persistent.
Karte 438
Frage
What do the external circuit and measuring device do in an electrochemical cell?
Antwort
The circuit carries electrons from anode to cathode; a voltmeter measures potential difference, while an ammeter in series measures current.
Karte 439
Frage
At constant temperature, how does increasing the volume available to a gas affect its entropy?
Antwort
Entropy increases because the gas particles can occupy more positions in the larger space, so more microstates are accessible.
Karte 440
Frage
How does reversing one coupled reaction affect its ΔG?
Antwort
It reverses the sign of that reaction's ΔG.
Karte 441
Frage
Why is n required in ΔG° = -nFE°?
Antwort
It is the moles of electrons transferred per balanced reaction, linking charge flow to reaction extent.
Karte 442
Frage
What makes an electrolytic cell operate?
Antwort
An external power source drives a thermodynamically unfavorable redox reaction; oxidation still occurs at the anode and reduction at the cathode.
Karte 443
Frage
In an Mⁿ⁺/M concentration cell, which half-cell is the anode: the dilute or concentrated ion solution?
Antwort
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.
Karte 444
Frage
How is deposited metal mass found from current and time?
Antwort
Find q = It, convert q/F to moles e⁻, use the half-reaction ratio to moles metal, then multiply by molar mass.
Karte 445
Frage
Given product S° total 500 J mol^-1 K^-1 and reactant total 420 J mol^-1 K^-1, what is ΔS°?
Antwort
+80 J mol^-1 K^-1.
Karte 446
Frage
How do electrode masses change in a Zn–Cu galvanic cell?
Antwort
The Zn anode loses mass as Zn → Zn²⁺ + 2e⁻, while the Cu cathode gains mass as Cu²⁺ + 2e⁻ → Cu.
Karte 447
Frage
What is ΔG° when ΔH° = 50 kJ mol^-1, ΔS° = 0.200 kJ mol^-1 K^-1, and T = 300 K?
Antwort
-10 kJ mol^-1, from ΔG° = 50 − (300)(0.200).
Karte 448
Frage
Why can temperature change a solid's solubility?
Antwort
Temperature changes the balance of ΔH and TΔS, so it changes the free energy of dissolution and the equilibrium constant.
Karte 449
Frage
What does the size of ΔG° relative to RT imply about K?
Antwort
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.
Karte 450
Frage
Bubbles form at an inert cathode in acidic solution; which half-reaction can explain them?
Antwort
2H⁺ + 2e⁻ → H₂(g). Gas evolution at the cathode can be direct evidence of reduction.
450 Karten
Advanced High School Chemistry Flashcards: Complete 9-Part Course Review
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