AP Chemistry Flashcards: Complete 9-Unit Course Review
Review all nine AP Chemistry units with 450 cards covering concepts, models, equations, calculation setup, and laboratory reasoning.
על החפיסה הזו
Review AP® Chemistry through 450 independently written English flashcards arranged in the course's nine-unit sequence. The deck moves from atomic structure and compound structure through properties of substances and mixtures, reactions, kinetics, thermochemistry, equilibrium, acids and bases, and thermodynamics and electrochemistry. Prerequisites come before dependent models and calculations.
What the cards practice
The cards use five 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. They cover 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. The deck excludes mechanical permutations, graph-dependent prompts that require a missing figure, copied test formats, long multipart derivations, and visual recall tied to third-party figures. The review scheduler handles long-term spacing after installation.
See the official AP Chemistry course page for College Board's current course requirements.
The Common knowledge · CC0 1.0 label applies only to the independently written prompts, answers, examples, organization, metadata, and inherited original cover, to the extent applicable rights exist. It does not claim ownership of scientific facts or equations.
This is an independent, unofficial study aid. It is not affiliated with, endorsed by, sponsored by, or official material from College Board or the AP Program. AP® is a trademark registered by the College Board, which is not affiliated with, and does not endorse, this product. No College Board examination questions, answer choices, scoring materials, curriculum text, logos, or trade dress were copied.
הכרטיסים בחפיסה הזו
כרטיס 1
שאלה
What does one mole count?
תשובה
Exactly 6.02214076 × 10^23 representative particles.
כרטיס 2
שאלה
What does a peak in an element's mass spectrum represent?
תשובה
An isotope with a particular mass-to-charge ratio; for singly charged monatomic ions, the position tracks isotopic mass.
כרטיס 3
שאלה
What does an empirical formula show?
תשובה
The lowest whole-number ratio of the elements' atoms in a compound.
כרטיס 4
שאלה
How does a mixture differ from a pure substance at the particle level?
תשובה
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.
כרטיס 5
שאלה
Which particles make up an atom's nucleus?
תשובה
Protons and neutrons. Electrons occupy the space outside the nucleus.
כרטיס 6
שאלה
What does a larger binding energy on a PES spectrum mean?
תשובה
More energy is required to remove that electron, so it is held more strongly by the nucleus.
כרטיס 7
שאלה
How does atomic radius generally change across a period and down a group?
תשובה
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.
כרטיס 8
שאלה
What typical ion charge do Group 1 metals form?
תשובה
+1, by losing their one valence electron.
כרטיס 9
שאלה
How do you convert moles to particles?
תשובה
Multiply by Avogadro's number: particles = moles × 6.022 × 10^23 mol^-1.
כרטיס 10
שאלה
How is average atomic mass estimated from isotope data?
תשובה
Add each isotopic mass multiplied by its fractional abundance.
כרטיס 11
שאלה
How is an element's mass percent in a compound calculated?
תשובה
Divide the mass contributed by that element by the compound's molar mass, then multiply by 100%.
כרטיס 12
שאלה
How can measured elemental composition reveal a sample's purity?
תשובה
Compare the measured mass fraction with the fraction expected for the pure compound; a mismatch indicates another component.
כרטיס 13
שאלה
How do you build a ground-state electron configuration with the Aufbau principle?
תשובה
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.
כרטיס 14
שאלה
What does the relative area or height of an ideal PES peak indicate?
תשובה
The relative number of electrons in the corresponding subshell.
כרטיס 15
שאלה
How does first ionization energy generally change across a period and down a group?
תשובה
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.
כרטיס 16
שאלה
Why do elements in the same group form similar compounds?
תשובה
Their ground-state valence patterns repeat, including which outer subshells are full or partly full. That leads to similar bonding and typical ion charges.
כרטיס 17
שאלה
How do you convert a sample's mass to moles?
תשובה
Divide its mass by its molar mass: n = m/M.
כרטיס 18
שאלה
Which mass-spectrum interpretation lies outside the usual single-element model used in this deck?
תשובה
Assigning peaks in mixtures or peaks from multiply charged or polyatomic species; the standard model uses singly charged monatomic ions of one element.
כרטיס 19
שאלה
What does the law of definite proportions state?
תשובה
Every pure sample of a given compound has the same element mass ratios.
כרטיס 20
שאלה
Why can two samples of the same mixture have different compositions?
תשובה
Mixture components are physically combined, so their relative amounts are not fixed by a chemical formula.
כרטיס 21
שאלה
How does Coulomb's law connect charge and separation to attraction?
תשובה
Attraction grows with the magnitude of the charge product and decreases with the square of the separation distance.
כרטיס 22
שאלה
Which PES electrons usually appear at the highest binding energy?
תשובה
Core electrons closest to the nucleus, because they feel the strongest nuclear attraction.
כרטיס 23
שאלה
How does electron affinity generally change across a period and down a group?
תשובה
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.
כרטיס 24
שאלה
Why are alkali metals generally more reactive down the group?
תשובה
Their valence electron is farther from the nucleus and easier to remove.
כרטיס 25
שאלה
How many moles are in 18.0 g of H₂O?
תשובה
About 0.999 mol. Use 18.0 g ÷ 18.02 g mol^-1.
כרטיס 26
שאלה
An element is 75% isotope 10 and 25% isotope 11; what is its average atomic mass?
תשובה
10.25 u. Calculate (0.75 × 10) + (0.25 × 11).
כרטיס 27
שאלה
A compound is 40.0% C, 6.7% H, and 53.3% O by mass; what is its empirical formula?
תשובה
CH₂O. For a 100 g sample, convert each mass to moles and divide by the smallest amount.
כרטיס 28
שאלה
A 10.0 g impure sample contains 8.5 g of the target compound; what is its mass-percent purity?
תשובה
85%. Calculate (8.5 g ÷ 10.0 g) × 100%.
כרטיס 29
שאלה
Which electrons are removed first when a transition metal forms a cation?
תשובה
Electrons in the occupied orbital with the highest principal quantum number: 4s before 3d. For example, Fe²⁺ is [Ar] 3d⁶.
כרטיס 30
שאלה
A PES spectrum has peaks proportional to 2, 2, and 6 electrons; which configuration fits?
תשובה
1s² 2s² 2p⁶, the configuration of Ne.
כרטיס 31
שאלה
How does electronegativity generally change across a period and down a group?
תשובה
It increases from left to right across a period and decreases down a group as atomic size and shielding increase.
כרטיס 32
שאלה
What empirical formula results from Al³⁺ and O²⁻?
תשובה
Al₂O₃, because two Al³⁺ ions balance three O²⁻ ions.
כרטיס 33
שאלה
How does a particle's mass in atomic mass units relate to its molar mass?
תשובה
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.
כרטיס 34
שאלה
What does the tallest isotope peak usually indicate in a simple mass spectrum?
תשובה
The most abundant isotope, assuming comparable detection response and singly charged ions.
כרטיס 35
שאלה
How much oxygen is present in 25.0 g of a compound that is 32.0% oxygen by mass?
תשובה
8.00 g O. Multiply 25.0 g by 0.320.
כרטיס 36
שאלה
What does a particle diagram with two unbonded species in changing ratios represent?
תשובה
A mixture, because more than one particle type is present and the ratio is not fixed in a formula unit.
כרטיס 37
שאלה
What distinguishes valence electrons from core electrons?
תשובה
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.
כרטיס 38
שאלה
Why can PES peak groups reveal an atom's occupied subshells?
תשובה
Electrons in different subshells require distinct removal energies, producing separate binding-energy groups.
כרטיס 39
שאלה
How do ion radii compare with neutral atoms and within an isoelectronic series?
תשובה
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.
כרטיס 40
שאלה
What formula is expected for a compound between a Group 2 metal M and a Group 17 nonmetal X?
תשובה
MX₂, because M forms M²⁺ and X forms X⁻.
כרטיס 41
שאלה
When is a covalent bond considered nonpolar?
תשובה
When the bonded atoms have identical or very similar electronegativities, so the shared electron density is distributed approximately evenly.
כרטיס 42
שאלה
Why does a bonded pair of atoms have an equilibrium bond length?
תשובה
At that separation, attractive and repulsive interactions balance at minimum potential energy.
כרטיס 43
שאלה
How are particles arranged in an ionic solid?
תשובה
Cations and anions occupy a repeating three-dimensional lattice held by electrostatic attraction.
כרטיס 44
שאלה
What model explains bonding in a metal?
תשובה
Positive metal cores are held together by attraction to mobile, delocalized valence electrons.
כרטיס 45
שאלה
How do you construct a Lewis diagram?
תשובה
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.
כרטיס 46
שאלה
What does resonance mean in a molecule or ion?
תשובה
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.
כרטיס 47
שאלה
What determines molecular shape in VSEPR theory?
תשובה
Electron domains around the central atom arrange to minimize repulsions.
כרטיס 48
שאלה
How does an ionic bond differ from a covalent bond?
תשובה
Ionic bonding is attraction among oppositely charged ions in an extended structure; covalent bonding uses shared electron density between atoms.
כרטיס 49
שאלה
What happens to potential energy when bonded atoms are pushed much closer than equilibrium?
תשובה
Potential energy rises sharply because nucleus–nucleus and electron–electron repulsions dominate.
כרטיס 50
שאלה
Why are many ionic solids brittle?
תשובה
A shifted lattice can align like charges, creating strong repulsion that splits the crystal.
כרטיס 51
שאלה
What molecular shapes arise from two electron domains with no lone pairs and from three domains with zero or one lone pair?
תשובה
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°.
כרטיס 52
שאלה
Why are metals electrically conductive as solids?
תשובה
Their delocalized electrons can move through the solid when an electric field is applied.
כרטיס 53
שאלה
How is formal charge calculated for an atom in a Lewis diagram?
תשובה
Formal charge = valence electrons − nonbonding electrons − half the bonding electrons.
כרטיס 54
שאלה
Why can't electronegativity difference alone classify a bond as ionic or covalent?
תשובה
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.
כרטיס 55
שאלה
Which shapes and bond-angle trends arise as lone pairs replace bonds in four electron domains?
תשובה
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.
כרטיס 56
שאלה
What feature of a potential-energy curve represents bond dissociation energy?
תשובה
The energy difference from the curve's minimum to the separated-atoms limit.
כרטיס 57
שאלה
When does an ionic compound conduct electricity?
תשובה
When molten or dissolved so its ions can move; not as a rigid solid lattice.
כרטיס 58
שאלה
What is a substitutional alloy?
תשובה
An alloy in which atoms of a similar size replace some host-metal atoms in the lattice.
כרטיס 59
שאלה
How do two, three, and four electron domains map to hybridization?
תשובה
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.
כרטיס 60
שאלה
What usually makes one resonance contributor more favorable than another?
תשובה
Smaller formal-charge magnitudes, appropriate negative charge on more electronegative atoms, and complete valence shells where applicable.
כרטיס 61
שאלה
How many sigma and pi bonds are in single, double, and triple bonds?
תשובה
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.
כרטיס 62
שאלה
Why is a polar covalent bond polar?
תשובה
Unequal electronegativity creates an uneven sharing of electron density and partial charges.
כרטיס 63
שאלה
Which molecular shapes arise as lone pairs replace bonds in five electron domains?
תשובה
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.
כרטיס 64
שאלה
How do ionic charge and ionic radius affect attraction between ions?
תשובה
Larger charge magnitudes and smaller ionic radii produce stronger attraction because the charge product increases and the ion centers are closer.
כרטיס 65
שאלה
Why do ionic solids often have high melting points?
תשובה
Many strong Coulombic attractions throughout the lattice must be overcome to free the ions.
כרטיס 66
שאלה
What is an interstitial alloy?
תשובה
A smaller atom occupies holes between host-metal atoms, often making lattice layers harder to slide.
כרטיס 67
שאלה
What shape has six bonding domains and no lone pairs on the central atom?
תשובה
Octahedral.
כרטיס 68
שאלה
Which elements commonly form incomplete octets in stable Lewis diagrams?
תשובה
Hydrogen forms a duet, and electron-deficient central atoms such as boron or beryllium can have fewer than eight electrons.
כרטיס 69
שאלה
How do bond order and atomic size affect covalent bond length and strength?
תשובה
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.
כרטיס 70
שאלה
What bonding model best fits a sample that is malleable and conducts as a solid?
תשובה
Metallic bonding with mobile, delocalized electrons and nondirectional attractions.
כרטיס 71
שאלה
What shape has six electron domains, five bonds, and one lone pair?
תשובה
Square pyramidal.
כרטיס 72
שאלה
Which lattice should have stronger attractions: MgO or NaCl, assuming similar separations?
תשובה
MgO, because the charge product for Mg²⁺ and O²⁻ is larger than for Na⁺ and Cl⁻.
כרטיס 73
שאלה
Why are pure metals often malleable?
תשובה
Metal cores can shift while the mobile electron sea maintains nondirectional attraction instead of exposing fixed like-charge planes.
כרטיס 74
שאלה
What is the best Lewis structure for CO₂?
תשובה
O=C=O, with two lone pairs on each oxygen and no formal charges.
כרטיס 75
שאלה
What shape has six electron domains, four bonds, and two opposite lone pairs?
תשובה
Square planar.
כרטיס 76
שאלה
What limitation does an odd total number of valence electrons create for a Lewis diagram?
תשובה
At least one electron must remain unpaired, so not every atom can have a complete paired-electron octet.
כרטיס 77
שאלה
What does a higher bond order do to a bond's potential-energy curve?
תשובה
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.
כרטיס 78
שאלה
When can a carbon–carbon double bond produce geometric isomers?
תשובה
When each carbon has two different substituents. The pi bond restricts rotation, so distinct spatial arrangements can persist.
כרטיס 79
שאלה
When may a third-period central atom exceed an octet in a Lewis diagram?
תשובה
When the valid electron count and lower formal charges favor an expanded valence shell, as in species such as SF₆.
כרטיס 80
שאלה
How do you decide whether a molecule with polar bonds is polar overall?
תשובה
Add the bond-dipole vectors using the molecular shape; symmetry may cancel them, while an asymmetric arrangement leaves a net dipole.
כרטיס 81
שאלה
Which interparticle forces act between all atoms and molecules?
תשובה
London dispersion forces, caused by temporary and induced dipoles.
כרטיס 82
שאלה
What four broad solid types does this deck compare?
תשובה
Ionic, metallic, molecular, and covalent-network solids.
כרטיס 83
שאלה
How do gas particles differ from liquid particles?
תשובה
Gas particles are much farther apart and move independently; liquid particles stay close but can move past one another.
כרטיס 84
שאלה
What relationship connects pressure, volume, amount, and temperature for an ideal gas?
תשובה
PV = nRT, with absolute temperature in kelvins and units consistent with R.
כרטיס 85
שאלה
What does temperature measure in kinetic molecular theory?
תשובה
The particles' average translational kinetic energy.
כרטיס 86
שאלה
What two ideal-gas assumptions fail most clearly for real gases?
תשובה
Particles have nonzero volume and experience intermolecular attractions.
כרטיס 87
שאלה
How is molarity defined?
תשובה
Moles of solute per liter of solution: M = n/V.
כרטיס 88
שאלה
What must a correct particulate diagram of NaCl(aq) show?
תשובה
Separated Na⁺ and Cl⁻ ions in a 1:1 ratio, each surrounded by oriented water molecules.
כרטיס 89
שאלה
Which separation method removes an insoluble solid from a liquid?
תשובה
Filtration: the solid stays as residue while the liquid passes as filtrate.
כרטיס 90
שאלה
What does “like dissolves like” mean at the particle level?
תשובה
A solute tends to dissolve when new solute–solvent attractions can compete with the attractions disrupted in the pure substances.
כרטיס 91
שאלה
What happens when matter absorbs electromagnetic radiation?
תשובה
Its particles move to an allowed higher-energy state when the photon energy matches the energy gap.
כרטיס 92
שאלה
Which equations connect photon energy, frequency, and wavelength?
תשובה
E = hν and c = λν.
כרטיס 93
שאלה
What is the Beer–Lambert law?
תשובה
A = εbc: absorbance equals molar absorptivity at the chosen wavelength times path length times concentration.
כרטיס 94
שאלה
What molecular features generally strengthen London dispersion forces?
תשובה
More electrons and a more polarizable cloud strengthen temporary dipoles; greater contact area and accessible π-electron density can also strengthen the attraction.
כרטיס 95
שאלה
Why do molecular solids usually have low melting points and fail to conduct electricity?
תשובה
Distinct molecules are held together by relatively weak intermolecular forces, while their valence electrons stay localized in bonds and lone pairs.
כרטיס 96
שאלה
How do particles move in a solid?
תשובה
They vibrate about fixed positions and do not translate past one another.
כרטיס 97
שאלה
What graph shapes connect V or P with T(K) or n for an ideal gas?
תשובה
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.
כרטיס 98
שאלה
At the same temperature, which gas has the greater average molecular speed: He or Xe?
תשובה
He. Both have the same average kinetic energy, but KE = ½mv² means the lower-mass particles move faster.
כרטיס 99
שאלה
Why do real gases deviate more at high pressure?
תשובה
Particles are crowded, so their own volume is no longer negligible compared with the container volume.
כרטיס 100
שאלה
Which relationship describes dilution when solute amount is conserved?
תשובה
M₁V₁ = M₂V₂.
כרטיס 101
שאלה
Why does an aqueous ionic solution conduct electricity?
תשובה
Dissolved ions are mobile and carry charge through the solution.
כרטיס 102
שאלה
Which property lets simple distillation separate two liquids?
תשובה
A sufficient difference in volatility or boiling point, so the vapor is enriched in the more volatile component.
כרטיס 103
שאלה
Why are many ionic compounds soluble in water but poorly soluble in a nonpolar solvent?
תשובה
Water can form strong ion–dipole attractions that stabilize separated ions; a nonpolar solvent cannot provide comparable attractions.
כרטיס 104
שאלה
Which molecular transition is commonly associated with microwave absorption?
תשובה
A transition between quantized rotational energy levels.
כרטיס 105
שאלה
What frequency corresponds to a 600. nm photon?
תשובה
5.00 × 10^14 s^-1. Use ν = c/λ with 600. nm = 6.00 × 10^-7 m.
כרטיס 106
שאלה
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?
תשובה
0.40. Use A = εbc.
כרטיס 107
שאלה
What conditions allow hydrogen bonding between two molecules?
תשובה
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.
כרטיס 108
שאלה
Why are covalent-network solids often very hard with high melting points?
תשובה
A continuous network of strong covalent bonds must be disrupted to deform or melt the solid.
כרטיס 109
שאלה
Why do a substance's solid and liquid phases usually have similar molar volumes?
תשובה
Their particles remain in close contact in both phases, even though liquid particles can move past one another.
כרטיס 110
שאלה
How is a gas mixture's total pressure related to its component pressures?
תשובה
Ptotal = ΣPi; each partial pressure is the pressure that component would exert alone in the same volume and temperature.
כרטיס 111
שאלה
What microscopic events create gas pressure?
תשובה
Gas particles collide with container walls and transfer momentum.
כרטיס 112
שאלה
Why do intermolecular attractions matter more for gases at low temperature?
תשובה
Particles move more slowly, so attractions can alter their paths and promote condensation.
כרטיס 113
שאלה
What is the final concentration after 50.0 mL of 2.00 M solution is diluted to 200.0 mL?
תשובה
0.500 M. Use M₂ = M₁V₁/V₂.
כרטיס 114
שאלה
What must a particulate representation of a solution communicate?
תשובה
The relative concentrations of its components and the particle-level interactions among those components.
כרטיס 115
שאלה
What causes components to separate in chromatography?
תשובה
They differ in attraction to the stationary phase and the mobile phase, so they travel at different rates.
כרטיס 116
שאלה
Why are many polar molecular solutes soluble in water?
תשובה
Dipole attractions or hydrogen bonds with water can replace the solute–solute and water–water attractions disrupted during mixing.
כרטיס 117
שאלה
Why does an atom produce discrete spectral lines?
תשובה
Its electrons can occupy only quantized energy levels, so only photons matching allowed energy differences are absorbed or emitted.
כרטיס 118
שאלה
How does photon energy change when frequency doubles?
תשובה
It doubles because E = hν.
כרטיס 119
שאלה
Why is a calibration curve useful in spectrophotometry?
תשובה
It relates measured absorbance to known concentrations, letting an unknown concentration be read by interpolation within the linear range.
כרטיס 120
שאלה
How does an ion–dipole attraction form, and how does it compare with dipole–dipole attraction?
תשובה
An ion attracts the oppositely charged end of a polar molecule. Ion–dipole attractions tend to be stronger than dipole–dipole attractions.
כרטיס 121
שאלה
Which solid type is usually both conductive and malleable?
תשובה
A metallic solid, because its delocalized electrons move and its nondirectional bonding tolerates layer shifts.
כרטיס 122
שאלה
How does a crystalline solid differ from an amorphous solid?
תשובה
A crystalline solid has long-range repeating order; an amorphous solid lacks that long-range periodic arrangement.
כרטיס 123
שאלה
How is a gas component's partial pressure found from mole fraction?
תשובה
Pi = XiPtotal.
כרטיס 124
שאלה
How does heating a fixed-volume gas affect its pressure in the ideal model?
תשובה
Pressure rises because faster particles collide with the walls more forcefully and frequently.
כרטיס 125
שאלה
Why can attractions make a real gas's measured pressure lower than the ideal prediction?
תשובה
Attractions pull approaching particles away from the walls, reducing momentum transfer during wall collisions.
כרטיס 126
שאלה
How many moles of ions result from complete dissolution of 0.20 mol CaCl₂?
תשובה
0.60 mol ions: 0.20 mol Ca²⁺ plus 0.40 mol Cl⁻.
כרטיס 127
שאלה
How should water orient around Cl⁻ in a particle model?
תשובה
Its partially positive hydrogen ends point toward Cl⁻.
כרטיס 128
שאלה
Can filtration separate dissolved components of a liquid solution?
תשובה
No. Dissolved particles pass through the filter with the solvent; filtration only retains an insoluble solid.
כרטיס 129
שאלה
Why do nonpolar molecular solutes often dissolve in nonpolar solvents?
תשובה
Both rely mainly on compatible London dispersion forces, so mixing can replace the attractions disrupted in the separate substances.
כרטיס 130
שאלה
What does a shorter absorbed wavelength imply about an energy transition?
תשובה
A larger energy gap because E = hc/λ.
כרטיס 131
שאלה
What is the energy of a photon with frequency 5.0 × 10^14 s^-1?
תשובה
3.3 × 10^-19 J. Multiply by Planck's constant: E = (6.626 × 10^-34 J·s)(5.0 × 10^14 s^-1).
כרטיס 132
שאלה
How does doubling cuvette path length affect absorbance in the linear Beer–Lambert range?
תשובה
Absorbance doubles if concentration and molar absorptivity stay constant.
כרטיס 133
שאלה
How can noncovalent interactions affect a large biomolecule?
תשובה
Attractions between molecules or between different regions of the same molecule help set its shape, which strongly affects its properties and function.
כרטיס 134
שאלה
Why does an ionic solid usually fail to conduct as a solid?
תשובה
Its ions are fixed in lattice positions. The same substance conducts when molten or dissolved because the ions can then move.
כרטיס 135
שאלה
Why does a gas have no definite shape or volume?
תשובה
Its widely spaced particles move constantly and experience minimal interparticle attraction, so they spread through the available container.
כרטיס 136
שאלה
What graph shapes show the inverse pressure–volume relationship for a fixed amount of ideal gas at constant temperature?
תשובה
A plot of P against V is a decreasing curve, while P against 1/V is a straight line through the origin.
כרטיס 137
שאלה
At the same temperature, do different ideal gases have different average kinetic energies?
תשובה
No. Average translational kinetic energy depends only on absolute temperature.
כרטיס 138
שאלה
Under which conditions is ideal-gas behavior most accurate?
תשובה
Low pressure and high temperature, where particles are far apart and attractions matter least.
כרטיס 139
שאלה
What particle-level feature distinguishes a solution from a heterogeneous mixture?
תשובה
A solution—whether solid, liquid, or gas—is uniform throughout; a heterogeneous mixture has regions or phases with different compositions.
כרטיס 140
שאלה
How should water orient around Na⁺ in a particulate model?
תשובה
Its partially negative oxygen end points toward Na⁺.
כרטיס 141
שאלה
In paper chromatography, why does one solute spot travel farther than another?
תשובה
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.
כרטיס 142
שאלה
What energy competition helps explain whether an ionic solid dissolves?
תשובה
The energy needed to separate lattice ions competes with the energy released when ion–solvent attractions form.
כרטיס 143
שאלה
Which molecular motions commonly absorb infrared radiation?
תשובה
Bond vibrations whose changing dipole can interact with the radiation.
כרטיס 144
שאלה
Why must wavelength be converted to meters in c = λν when c is in m s^-1?
תשובה
Consistent units are required so meters cancel correctly and frequency comes out in s^-1.
כרטיס 145
שאלה
How can fingerprints on a cuvette affect a visible-light absorbance reading?
תשובה
They can absorb or scatter extra light, making measured absorbance too high and the inferred concentration too high.
כרטיס 146
שאלה
What causes and controls the strength of dipole–dipole attractions?
תשובה
Opposite partial charges on neighboring polar molecules attract. Strength increases with larger molecular dipoles and depends on how favorably the dipoles are oriented.
כרטיס 147
שאלה
Why is graphite conductive and soft while diamond is insulating and hard?
תשובה
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.
כרטיס 148
שאלה
Why are gases much more compressible than liquids?
תשובה
Gas particles have large empty spaces between them; liquid particles are already close together.
כרטיס 149
שאלה
What volume does 0.500 mol CO₂ occupy at 1.00 atm and 300. K if it behaves ideally?
תשובה
12.3 L. Use V = nRT/P = (0.500 mol)(0.08206 L atm mol^-1 K^-1)(300. K)/(1.00 atm).
כרטיס 150
שאלה
Why does a lighter gas effuse faster than a heavier gas at the same temperature?
תשובה
Its particles have a higher average speed because equal average kinetic energy is shared by less mass.
כרטיס 151
שאלה
How does finite particle volume affect a real gas at very high pressure?
תשובה
The free volume available for particle motion is smaller than the container volume assumed by the ideal model.
כרטיס 152
שאלה
How should 250.0 mL of 0.100 M NaCl be prepared from solid NaCl?
תשובה
Dissolve 0.0250 mol NaCl, or 1.46 g, then dilute to exactly 250.0 mL in a volumetric flask.
כרטיס 153
שאלה
What changes in a particle diagram when a solution is diluted without losing solute?
תשובה
The solute-particle count stays constant while solvent volume and particle spacing increase.
כרטיס 154
שאלה
Why is fractional distillation better than simple distillation for liquids with close boiling points?
תשובה
Repeated vaporization–condensation steps enrich the vapor in the more volatile component more effectively.
כרטיס 155
שאלה
Why are oil and water usually immiscible?
תשובה
Water's strong hydrogen-bond network isn't replaced by equally strong water–oil attractions, so the substances separate into phases.
כרטיס 156
שאלה
Which molecular transition is commonly associated with ultraviolet or visible absorption?
תשובה
A transition between electronic energy levels.
כרטיס 157
שאלה
Which photon carries more energy, blue light or red light?
תשובה
Blue light, because it has shorter wavelength and higher frequency.
כרטיס 158
שאלה
Why is absorbance often measured at the wavelength of maximum absorbance in Beer–Lambert analysis?
תשובה
It gives the largest concentration-sensitive signal, and the flat top near the maximum makes small wavelength-setting errors less influential.
כרטיס 159
שאלה
What creates a dipole–induced-dipole attraction, and what controls its strength?
תשובה
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.
כרטיס 160
שאלה
How do stronger intermolecular forces affect vapor pressure, boiling point, and melting point?
תשובה
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.
כרטיס 161
שאלה
How do particles behave in a liquid?
תשובה
They stay in close contact while moving and colliding continuously. Temperature and interparticle attractions affect their arrangement and motion.
כרטיס 162
שאלה
Why must Celsius temperature be converted to kelvins in gas-law calculations?
תשובה
Gas-law proportionalities require an absolute temperature scale whose zero corresponds to zero extrapolated thermal motion.
כרטיס 163
שאלה
How does raising temperature change a Maxwell–Boltzmann speed distribution?
תשובה
The distribution broadens, its peak lowers and shifts right, and a larger fraction of particles have high speed.
כרטיס 164
שאלה
Why does the ideal-gas model treat collisions as elastic?
תשובה
It assumes total kinetic energy is conserved in particle–particle and particle–wall collisions.
כרטיס 165
שאלה
How many moles of solute are in 75.0 mL of a 0.400 M solution?
תשובה
0.0300 mol. Multiply 0.400 mol L^-1 by 0.0750 L.
כרטיס 166
שאלה
For equal solution volumes drawn at the same scale, what shows which solution is more concentrated?
תשובה
The more concentrated diagram contains more solute particles in that equal volume.
כרטיס 167
שאלה
How do differences in intermolecular attractions let distillation separate a liquid solution?
תשובה
They give the components different vapor pressures, so the vapor is enriched in the more volatile component.
כרטיס 168
שאלה
What comparison helps predict whether two liquids will be miscible?
תשובה
Liquids with similar types and strengths of intermolecular attractions are more likely to mix uniformly.
כרטיס 169
שאלה
How can an absorption spectrum help identify a substance?
תשובה
Its allowed energy gaps produce a characteristic pattern of absorbed wavelengths that can be compared with known spectra.
כרטיס 170
שאלה
How does absorbing or emitting a photon change an atom's or molecule's energy?
תשובה
Absorption raises the species' energy by exactly the photon energy; emission lowers it by the same amount.
כרטיס 171
שאלה
What macroscopic evidence can support that a chemical reaction occurred?
תשובה
Evidence can include gas formation, precipitate formation, a persistent color change, or an energy change, interpreted with particle-level changes.
כרטיס 172
שאלה
What does a net ionic equation include?
תשובה
Only the dissolved or reacting species that undergo chemical change; spectator ions are omitted.
כרטיס 173
שאלה
What must a correct particulate reaction diagram conserve?
תשובה
The number of atoms of every element and the total charge.
כרטיס 174
שאלה
What distinguishes a chemical change from a physical change?
תשובה
A chemical change rearranges bonds into new substances; a physical change alters state or arrangement without changing chemical identity.
כרטיס 175
שאלה
What does a balanced equation's coefficient ratio provide?
תשובה
The mole ratio among reacting and produced species.
כרטיס 176
שאלה
What is the equivalence point of a titration?
תשובה
The point where titrant and analyte have reacted in the stoichiometric ratio given by the balanced equation.
כרטיס 177
שאלה
What defines a precipitation reaction?
תשובה
Aqueous ions combine to form a sparingly soluble solid.
כרטיס 178
שאלה
What happens in a Brønsted–Lowry acid–base reaction?
תשובה
A proton transfers from the acid (donor) to the base (acceptor). In aqueous solution, H₂O can play either role.
כרטיס 179
שאלה
What does oxidation mean in a redox reaction?
תשובה
Loss of electrons and an increase in oxidation number.
כרטיס 180
שאלה
What particle-level change confirms that a process is chemical?
תשובה
Atoms rearrange into new combinations, producing substances with different compositions.
כרטיס 181
שאלה
Which ions are spectators when AgNO₃(aq) reacts with NaCl(aq)?
תשובה
Na⁺ and NO₃⁻. The net ionic reaction is Ag⁺(aq) + Cl⁻(aq) → AgCl(s).
כרטיס 182
שאלה
How does a particulate diagram reveal the limiting reactant?
תשובה
After forming the maximum product allowed by the ratio, none of the limiting reactant remains while excess reactant particles do.
כרטיס 183
שאלה
Is melting ice a chemical or physical change?
תשובה
A physical change. H₂O molecules remain H₂O while their arrangement and motion change.
כרטיס 184
שאלה
How is the limiting reactant identified from given amounts?
תשובה
Convert each reactant to the same product amount using the balanced equation; the smaller product amount identifies the limiting reactant.
כרטיס 185
שאלה
How does an endpoint differ from an equivalence point?
תשובה
The endpoint is an observed signal such as indicator color change; the equivalence point is the exact stoichiometric condition.
כרטיס 186
שאלה
How is complete combustion of a hydrocarbon in excess oxygen classified, and what products form?
תשובה
It is a redox combustion reaction that forms CO₂ and H₂O.
כרטיס 187
שאלה
What are the conjugate acid and conjugate base in NH₃ + H₂O ⇌ NH₄⁺ + OH⁻?
תשובה
NH₄⁺ is the conjugate acid of NH₃, and OH⁻ is the conjugate base of H₂O.
כרטיס 188
שאלה
What does reduction mean in a redox reaction?
תשובה
Gain of electrons and a decrease in oxidation number.
כרטיס 189
שאלה
Which common changes are physical rather than chemical?
תשובה
Phase changes and the formation or separation of mixtures are physical when each substance keeps its composition.
כרטיס 190
שאלה
How are strong soluble electrolytes written in a complete ionic equation?
תשובה
As separated aqueous ions; solids, liquids, gases, and weak electrolytes stay intact.
כרטיס 191
שאלה
A diagram starts with six A particles and four B₂ particles for 2A + B₂ → 2AB; what remains after completion?
תשובה
One B₂ remains. Six A consume three B₂ and form six AB.
כרטיס 192
שאלה
Why is dissolving NaCl in water normally classified as a physical change?
תשובה
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.
כרטיס 193
שאלה
What mass of AgCl can form from 25.0 mL of 0.200 M AgNO₃ mixed with excess Cl⁻?
תשובה
0.717 g AgCl. The 1:1 reaction gives 0.00500 mol AgCl; multiply by 143.32 g mol^-1.
כרטיס 194
שאלה
What calculation finds unknown analyte moles at equivalence?
תשובה
Use titrant moles, n = MV, then apply the balanced-reaction mole ratio.
כרטיס 195
שאלה
Which feature identifies an acid–base, redox, or precipitation reaction?
תשובה
Acid–base reactions transfer protons, redox reactions change oxidation numbers through electron transfer, and precipitation reactions form a sparingly soluble solid.
כרטיס 196
שאלה
What is the net ionic equation for strong acid–strong base neutralization?
תשובה
H⁺(aq) + OH⁻(aq) → H₂O(l).
כרטיס 197
שאלה
What is the oxidation number of sulfur in SO₄²⁻?
תשובה
+6. Four oxygens contribute -8 total, so sulfur must be +6 to give -2 overall.
כרטיס 198
שאלה
Why can gas bubbles alone be ambiguous evidence of reaction?
תשובה
Bubbles may also come from boiling or dissolved gas escaping, so the context and particle identities must support a chemical change.
כרטיס 199
שאלה
How is melting ice represented as a balanced physical-change equation?
תשובה
H₂O(s) → H₂O(l). The formula and atom count stay the same because only the physical state changes.
כרטיס 200
שאלה
What does a particle diagram show when no reaction occurs after two aqueous ionic solutions mix?
תשובה
All ions remain separated and solvated, with no new bonded particles, precipitate, or gas.
כרטיס 201
שאלה
Why is rusting iron a chemical change?
תשובה
Iron atoms form new iron-oxide substances through electron transfer and new bonding.
כרטיס 202
שאלה
For 2H₂O₂(aq) → 2H₂O(l) + O₂(g), what volume of O₂ forms from 0.100 mol H₂O₂ at 298 K and 1.00 atm?
תשובה
1.22 L O₂. The mole ratio gives 0.0500 mol O₂, then V = nRT/P.
כרטיס 203
שאלה
A 25.0 mL monoprotic acid sample requires 20.0 mL of 0.150 M NaOH; what is the acid concentration?
תשובה
0.120 M. At 1:1 equivalence, moles acid = 0.0200 L × 0.150 M, then divide by 0.0250 L.
כרטיס 204
שאלה
Which salts does the minimum solubility rule in this deck treat as soluble?
תשובה
All salts containing Na⁺, K⁺, NH₄⁺, or NO₃⁻ are treated as soluble in water.
כרטיס 205
שאלה
How are the strengths of a conjugate acid and its conjugate base related?
תשובה
A stronger acid has a weaker conjugate base, and a stronger base has a weaker conjugate acid.
כרטיס 206
שאלה
How are oxidation and reduction half-reactions combined into one balanced equation?
תשובה
Multiply them so electrons lost equal electrons gained, add the half-reactions, then cancel electrons and any identical species on both sides.
כרטיס 207
שאלה
How do molecular, complete ionic, and net ionic equations differ?
תשובה
Molecular equations keep compounds intact, complete ionic equations split strong soluble electrolytes, and net ionic equations remove spectators. All three conserve atoms and charge.
כרטיס 208
שאלה
How should coefficients change particle counts in a reaction diagram?
תשובה
They set whole-particle ratios while preserving each particle's chemical formula.
כרטיס 209
שאלה
Is separating a mixture by distillation a chemical or physical change?
תשובה
A physical change. Components change phase and location but keep their chemical identities.
כרטיס 210
שאלה
What equation results from Cu → Cu²⁺ + 2e⁻ and Ag⁺ + e⁻ → Ag?
תשובה
Cu + 2Ag⁺ → Cu²⁺ + 2Ag. Multiply the silver half-reaction by 2 and cancel 2e⁻; both atom counts and net charge then match.
כרטיס 211
שאלה
How is average reaction rate found from a reactant concentration?
תשובה
Use the negative concentration change divided by elapsed time, adjusted by its stoichiometric coefficient when comparing species rates.
כרטיס 212
שאלה
What does a rate law express?
תשובה
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.
כרטיס 213
שאלה
A plot of ln[A] versus time is linear; what is the order in A and its integrated rate law?
תשובה
First order: ln[A]t = ln[A]0 − kt, so the plot's slope is −k.
כרטיס 214
שאלה
What is an elementary reaction?
תשובה
A single step in a mechanism whose rate law follows directly from its reactant molecularity.
כרטיס 215
שאלה
What two collision conditions are needed for reaction?
תשובה
Sufficient collision energy and a productive molecular orientation.
כרטיס 216
שאלה
What does activation energy represent on a reaction-energy profile?
תשובה
The energy difference from the reactants to the transition state. The reaction coordinate tracks the step's structural progress, not elapsed time.
כרטיס 217
שאלה
What must the elementary steps of a valid mechanism do when added?
תשובה
Cancel intermediates and reproduce the overall balanced reaction.
כרטיס 218
שאלה
How is a proposed mechanism tested against kinetics?
תשובה
Its derived rate law must agree with the experimentally measured rate law.
כרטיס 219
שאלה
What does a pre-equilibrium approximation assume?
תשובה
A fast reversible step reaches equilibrium before a later slow step consumes its intermediate.
כרטיס 220
שאלה
What does each peak on a multistep energy profile represent?
תשובה
A transition state for one elementary step.
כרטיס 221
שאלה
How does a catalyst increase reaction rate?
תשובה
It provides an alternate mechanism with a lower activation-energy pathway.
כרטיס 222
שאלה
Why does crushing a solid reactant usually increase its reaction rate?
תשובה
Crushing increases exposed surface area, so more reactant particles can collide with the other reactant each second.
כרטיס 223
שאלה
How is reaction order found from initial-rate data?
תשובה
Compare trials where one reactant concentration changes while the others stay constant, then match the rate factor to the concentration factor.
כרטיס 224
שאלה
A plot of [A] versus time is linear; what is the order in A and its integrated rate law?
תשובה
Zero order: [A]t = [A]0 − kt, so the plot's slope is −k.
כרטיס 225
שאלה
What is the rate law for the elementary step 2A + B → products?
תשובה
rate = k[A]²[B]. This inference is valid because the step is elementary.
450 כרטיסים
AP Chemistry Flashcards: Complete 9-Unit Course Review
ללמוד את החפיסה הזו בחינםNibomo תיפתח כדי שתוכל להתחיל ללמוד.
כרטיס 226
שאלה
How does raising temperature change a Maxwell–Boltzmann energy distribution and reaction rate?
תשובה
The distribution shifts and broadens toward higher energies, so a larger fraction of collisions exceeds the activation-energy threshold and can react.
כרטיס 227
שאלה
How is ΔH read from a reaction-energy profile?
תשובה
ΔH = energy of products − energy of reactants.
כרטיס 228
שאלה
What is a reaction intermediate?
תשובה
A species formed in one mechanism step and consumed in a later step, so it cancels from the overall equation.
כרטיס 229
שאלה
Why can't overall reaction coefficients usually supply rate-law exponents?
תשובה
The overall equation hides the mechanism; exponents come from experiment unless the reaction is a stated elementary step.
כרטיס 230
שאלה
How does pre-equilibrium remove an intermediate from a rate law?
תשובה
Use the fast-step equilibrium relation to express the intermediate concentration in terms of stable reactants.
כרטיס 231
שאלה
What does each valley between peaks represent on a multistep profile?
תשובה
A reaction intermediate.
כרטיס 232
שאלה
Does a catalyst change ΔH or the equilibrium constant?
תשובה
No. It changes the pathway and rates, not reactant/product energies or the equilibrium composition.
כרטיס 233
שאלה
For 2A → B, how are disappearance of A and appearance of B related?
תשובה
Reaction rate = -(1/2)Δ[A]/Δt = Δ[B]/Δt.
כרטיס 234
שאלה
How do the units of k depend on a rate law's overall order?
תשובה
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.
כרטיס 235
שאלה
A plot of 1/[A] versus time is linear; what is the order in A and its integrated rate law?
תשובה
Second order: 1/[A]t = 1/[A]0 + kt, so the plot's slope is +k.
כרטיס 236
שאלה
What is molecularity?
תשובה
The number of reacting particles in an elementary step, such as unimolecular or bimolecular.
כרטיס 237
שאלה
How does raising temperature affect k in the qualitative Arrhenius model?
תשובה
k increases, often sharply, because a larger fraction of collisions can reach the transition state. Arrhenius-equation calculations are outside this deck’s scope.
כרטיס 238
שאלה
A reactant falls from 0.80 M to 0.50 M in 30. s; what is its average disappearance rate to two significant figures?
תשובה
0.010 M s^-1. Use -(0.50 − 0.80) M ÷ 30. s.
כרטיס 239
שאלה
How does a catalyst differ from an intermediate in a mechanism?
תשובה
A catalyst is consumed early and regenerated later; an intermediate is formed early and consumed later.
כרטיס 240
שאלה
For 2NO₂ → NO₃ + NO (slow), followed by NO₃ + CO → NO₂ + CO₂ (fast), what rate law is predicted?
תשובה
rate = k[NO₂]². The first step is elementary and rate-limiting, so its molecularity sets the observed rate law.
כרטיס 241
שאלה
On a multistep reaction-energy profile, which feature often identifies the rate-determining step?
תשובה
The step with the largest activation barrier measured from its preceding valley to its peak.
כרטיס 242
שאלה
If changing [B] leaves rate unchanged, what is the order in B?
תשובה
Zero order, so [B]^0 = 1 in the measured rate law.
כרטיס 243
שאלה
What mechanism changes can binding, acid–base, or surface catalysis introduce?
תשובה
They can orient reactants, lower activation barriers, or create new bound, protonated, or deprotonated intermediates and elementary steps; the catalyst is regenerated.
כרטיס 244
שאלה
What is special about a first-order reaction's half-life?
תשובה
It is constant and independent of starting concentration: t1/2 = ln 2/k. Radioactive decay is a common first-order example.
כרטיס 245
שאלה
Why is a termolecular elementary collision uncommon?
תשובה
Three particles must collide simultaneously with suitable energy and orientation, which is much less probable than one- or two-particle events.
כרטיס 246
שאלה
On a reaction-energy profile, how are reverse activation energy, forward activation energy, and ΔH related?
תשובה
Ea,reverse = Ea,forward − ΔH. The reverse barrier is measured from products to the same transition state.
כרטיס 247
שאלה
Why can correct orientation matter even above the activation energy?
תשובה
The colliding reactive sites must align so old bonds can break and new bonds can form along the reaction pathway.
כרטיס 248
שאלה
How does detecting a proposed reaction intermediate affect a mechanism claim?
תשובה
It supports a mechanism that contains that intermediate, but it doesn't prove that mechanism is unique.
כרטיס 249
שאלה
For 2NO ⇌ N₂O₂ (fast equilibrium), followed by N₂O₂ + O₂ → 2NO₂ (slow), what observed rate law results?
תשובה
rate = kobs[NO]²[O₂]. Start with rate = k₂[N₂O₂][O₂], use [N₂O₂] = K[NO]² from the fast equilibrium, then substitute.
כרטיס 250
שאלה
What does the highest point of a one-step energy profile represent?
תשובה
The transition state, an unstable arrangement at the top of the activation barrier.
כרטיס 251
שאלה
What sign does q have for an endothermic system?
תשובה
Positive, because the system absorbs heat from the surroundings.
כרטיס 252
שאלה
How does an exothermic reaction appear on an enthalpy diagram?
תשובה
Products lie below reactants, so ΔH is negative.
כרטיס 253
שאלה
What condition defines thermal equilibrium?
תשובה
Objects in contact have the same temperature, so there is no net heat transfer.
כרטיס 254
שאלה
What equations relate heat capacity and temperature change to heat transfer?
תשובה
Use q = mcΔT with specific heat capacity, or q = nCₘΔT with molar heat capacity.
כרטיס 255
שאלה
Why is temperature constant during a phase-change plateau?
תשובה
Added or removed energy changes interparticle potential energy instead of average kinetic energy.
כרטיס 256
שאלה
What does ΔHrxn describe?
תשובה
The heat absorbed or released at constant pressure for the reaction exactly as written under the stated conditions.
כרטיס 257
שאלה
How is reaction enthalpy estimated from average bond enthalpies?
תשובה
ΔHrxn ≈ Σ(bonds broken) − Σ(bonds formed).
כרטיס 258
שאלה
What is the standard enthalpy of formation of an element in its standard state?
תשובה
Zero by definition.
כרטיס 259
שאלה
In a Hess’s law calculation, how should a step change when the target needs twice its reverse?
תשובה
Reverse the equation, double every coefficient, and multiply its ΔH by -2.
כרטיס 260
שאלה
How can energy cross a system boundary during a process?
תשובה
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.
כרטיס 261
שאלה
How does an endothermic reaction appear on an enthalpy diagram?
תשובה
Products lie above reactants, so ΔH is positive.
כרטיס 262
שאלה
How are heat gained by a system and heat lost by its surroundings related in an isolated setup?
תשובה
qsystem = -qsurroundings.
כרטיס 263
שאלה
In coffee-cup calorimetry, how is reaction heat related to solution heat?
תשובה
qrxn = -qsolution when calorimeter heat is negligible and pressure is constant.
כרטיס 264
שאלה
What heat is required to melt n moles at the melting point?
תשובה
q = nΔHfus.
כרטיס 265
שאלה
How does reversing a reaction change ΔH?
תשובה
It reverses the sign of ΔH.
כרטיס 266
שאלה
Why is breaking a bond endothermic?
תשובה
Energy must be supplied to separate atoms against their bonding attraction.
כרטיס 267
שאלה
How is ΔH°rxn calculated from standard enthalpies of formation?
תשובה
ΣνΔHf°(products) − ΣνΔHf°(reactants).
כרטיס 268
שאלה
How does multiplying an equation by 3 affect its ΔH?
תשובה
Multiply ΔH by 3 because enthalpy change scales with reaction amount.
כרטיס 269
שאלה
Why can an exothermic dissolution warm the solution?
תשובה
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.
כרטיס 270
שאלה
Does an energy diagram's activation barrier determine ΔH?
תשובה
No. ΔH depends on reactant and product energy levels, while the barrier controls kinetics.
כרטיס 271
שאלה
Why does heat flow from a warmer object to a cooler object?
תשובה
Energy transfers through collisions until their average kinetic energies, and therefore temperatures, equalize.
כרטיס 272
שאלה
How much heat warms 100.0 g of water by 5.0°C?
תשובה
2.1 kJ. Use q = (100.0 g)(4.184 J g^-1 °C^-1)(5.0°C).
כרטיס 273
שאלה
How are the molar enthalpies of a phase change and its reverse related?
תשובה
They have equal magnitudes and opposite signs, such as ΔHcond = -ΔHvap and ΔHfreeze = -ΔHfus.
כרטיס 274
שאלה
How does doubling every coefficient in a thermochemical equation affect ΔH?
תשובה
It doubles ΔH.
כרטיס 275
שאלה
Why is forming a bond exothermic?
תשובה
Atoms move to a lower-potential-energy bonded arrangement and release energy.
כרטיס 276
שאלה
What formation equation defines ΔHf° for CO₂(g)?
תשובה
C(s, graphite) + O₂(g) → CO₂(g), forming exactly one mole from elements in standard states.
כרטיס 277
שאלה
What should happen to intermediate species when equations in a Hess’s law calculation are added?
תשובה
They cancel, leaving the target overall reaction.
כרטיס 278
שאלה
If the surroundings warm during a process, what is the likely sign of qsystem?
תשובה
Negative; the system likely released heat to the surroundings.
כרטיס 279
שאלה
For a profile with reactants at 40 kJ and products at 10 kJ, what is ΔH?
תשובה
-30 kJ for the reaction as drawn.
כרטיס 280
שאלה
Assuming no phase change, what determines the final temperature when two substances exchange heat in an insulated container?
תשובה
Energy conservation: q_warm + q_cool = 0. Use each substance's mass, heat capacity, and initial temperature to solve for the common final temperature.
כרטיס 281
שאלה
How would heat loss to the room affect an exothermic calorimetry result?
תשובה
The observed temperature rise is too small, so the calculated magnitude of released heat is too low.
כרטיס 282
שאלה
What heat expression covers warming a liquid without a phase change?
תשובה
q = mcΔT, not nΔHphase.
כרטיס 283
שאלה
If forming 1 mol of product has ΔH = -50 kJ mol^-1, what is q when 2 mol forms?
תשובה
-100 kJ. Use q = nΔH = (2 mol)(-50 kJ mol^-1).
כרטיס 284
שאלה
Breaking reactant bonds requires 500 kJ, and forming product bonds releases 650 kJ; what is the estimated ΔH?
תשובה
-150 kJ, from 500 − 650.
כרטיס 285
שאלה
For CO(g) + ½O₂(g) → CO₂(g), what is ΔH°rxn if ΔHf°[CO] = -110.5 and ΔHf°[CO₂] = -393.5 kJ mol^-1?
תשובה
-283.0 kJ. Use -393.5 - [-110.5 + ½(0)], since ΔHf°[O₂(g)] = 0.
כרטיס 286
שאלה
In a Hess’s law calculation, two valid steps have ΔH values +25 kJ and -60 kJ; what is the combined ΔH?
תשובה
-35 kJ, provided the equations add to the target reaction.
כרטיס 287
שאלה
Why is “bonds breaking releases energy” incorrect?
תשובה
Bond breaking absorbs energy; the overall reaction releases energy only when forming new bonds releases more than breaking old bonds requires.
כרטיס 288
שאלה
How would melting appear on an energy diagram?
תשובה
The liquid lies above the solid, so ΔHfus is positive; the diagram represents a physical, endothermic change.
כרטיס 289
שאלה
Can two objects at the same temperature exchange energy microscopically?
תשובה
Yes, but their energy transfers balance, so there is no net heat flow.
כרטיס 290
שאלה
Why must the calorimeter's heat capacity be included when it isn't negligible?
תשובה
The apparatus can absorb or release heat, so include q_cal = C_calΔT in the energy balance: q_process + q_solution + q_cal = 0.
כרטיס 291
שאלה
What makes chemical equilibrium dynamic?
תשובה
Forward and reverse reactions continue at equal rates even though macroscopic concentrations stay constant.
כרטיס 292
שאלה
For aA + bB ⇌ cC, what is the concentration-form expression for Q?
תשובה
Q = [C]^c / ([A]^a[B]^b), using current rather than necessarily equilibrium concentrations.
כרטיס 293
שאלה
What does K much greater than 1 indicate?
תשובה
Products predominate at equilibrium, though K says nothing about reaction speed.
כרטיס 294
שאלה
How does reversing a reaction change its equilibrium constant?
תשובה
K becomes 1/K.
כרטיס 295
שאלה
Can a reversible system reach equilibrium when it starts with only products?
תשובה
Yes, if the reverse reaction is possible. The equilibrium composition depends on temperature, initial amounts, and volume or pressure.
כרטיס 296
שאלה
How do Q and K predict reaction direction?
תשובה
Q < K shifts forward, Q > K shifts reverse, and Q = K means equilibrium.
כרטיס 297
שאלה
Which species are omitted from a heterogeneous equilibrium expression?
תשובה
Pure solids and pure liquids because their activities are effectively constant.
כרטיס 298
שאלה
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?
תשובה
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.
כרטיס 299
שאלה
What does a flat concentration-time graph mean at equilibrium?
תשובה
Each concentration is constant, not necessarily equal to the others.
כרטיס 300
שאלה
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?
תשובה
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.
כרטיס 301
שאלה
What can Ksp tell you about a salt's solubility, and when can two Ksp values be compared directly?
תשובה
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.
כרטיס 302
שאלה
What is the common-ion effect on solubility?
תשובה
Adding an ion already in the dissolution equilibrium usually decreases the solid's molar solubility.
כרטיס 303
שאלה
How does uniform dilution shift an aqueous equilibrium based on the stoichiometric powers in Q?
תשובה
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.
כרטיס 304
שאלה
What happens if a reversible reaction starts with reactants only?
תשובה
The forward rate is initially largest; products form, the reverse rate grows, and the rates eventually become equal.
כרטיס 305
שאלה
What is the purpose of an ICE table?
תשובה
To organize initial, change, and equilibrium concentrations using reaction stoichiometry.
כרטיס 306
שאלה
Can a reaction with a very large K be slow?
תשובה
Yes. K describes thermodynamic equilibrium position, while rate depends on kinetics and activation energy.
כרטיס 307
שאלה
What happens to Q immediately after product concentration increases?
תשובה
Q increases; if it rises above K, the reaction shifts toward reactants.
כרטיס 308
שאלה
How does multiplying every reaction coefficient by 2 affect K?
תשובה
The new equilibrium constant is K².
כרטיס 309
שאלה
For A ⇌ B, Kc = 4.0 and initially [A] = 1.0 M and [B] = 0, what are the equilibrium concentrations?
תשובה
[A] = 0.20 M and [B] = 0.80 M. Let x form: Kc = x/(1.0 − x) = 4.0, so x = 0.80 M.
כרטיס 310
שאלה
What macroscopic properties stay constant at equilibrium?
תשובה
Properties such as concentration, color, and pressure remain constant when external conditions are fixed.
כרטיס 311
שאלה
How does decreasing volume shift a gaseous equilibrium?
תשובה
Toward the side with fewer moles of gas, if the two sides have different gaseous mole counts.
כרטיס 312
שאלה
For N₂ + 3H₂ ⇌ 2NH₃, what is Kc?
תשובה
Kc = [NH₃]² / ([N₂][H₂]³).
כרטיס 313
שאלה
For CaF₂(s) ⇌ Ca²⁺ + 2F⁻, how is Ksp written in terms of molar solubility s in pure water?
תשובה
Ksp = s(2s)² = 4s³ because [Ca²⁺] = s and [F⁻] = 2s.
כרטיס 314
שאלה
What does K much less than 1 indicate?
תשובה
Reactants predominate at equilibrium.
כרטיס 315
שאלה
How does decreasing a dissolved product's concentration or a gaseous product's partial pressure affect equilibrium when other Q terms are initially unchanged?
תשובה
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.
כרטיס 316
שאלה
Does equilibrium mean the reaction has stopped?
תשובה
No. Both directions continue, but equal rates produce no net macroscopic change.
כרטיס 317
שאלה
Why does adding NaF reduce CaF₂ solubility?
תשובה
The added F⁻ raises Qsp, shifting the dissolution equilibrium toward solid CaF₂.
כרטיס 318
שאלה
For N₂ + 3H₂ ⇌ 2NH₃, what is Kp when P_N₂ = 0.50 atm, P_H₂ = 1.50 atm, and P_NH₃ = 0.25 atm?
תשובה
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.
כרטיס 319
שאלה
What happens to Q when a gaseous equilibrium mixture is compressed at constant temperature if products have fewer gas moles?
תשובה
Q falls relative to K, so the reaction shifts toward products.
כרטיס 320
שאלה
How do K and Q transform when a reaction is reversed, its coefficients are multiplied, or reactions are added?
תשובה
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.
כרטיס 321
שאלה
When is the small-x approximation acceptable?
תשובה
When x is small relative to the initial concentration and the final result confirms the neglected change is suitably small.
כרטיס 322
שאלה
What graph feature shows a disturbance followed by re-equilibration?
תשובה
A sudden or gradual concentration change followed by new constant plateaus while rates return to equality.
כרטיס 323
שאלה
If Q = 0.20 and K = 5.0, which direction is favored next?
תשובה
Forward, because Q < K.
כרטיס 324
שאלה
At equilibrium, are reactant and product concentrations equal?
תשובה
Not necessarily. They are constant, while forward and reverse rates are equal.
כרטיס 325
שאלה
CaF₂ has Ksp = 3.2 × 10^-11 in pure water; what is its molar solubility?
תשובה
2.0 × 10^-4 M. If the molar solubility is s, then [Ca²⁺] = s, [F⁻] = 2s, and Ksp = 4s³.
כרטיס 326
שאלה
For N₂ + 3H₂ ⇌ 2NH₃, how is Qp written?
תשובה
Qp = (P_NH₃)²/[(P_N₂)(P_H₂)³], using the current partial pressures rather than necessarily equilibrium values.
כרטיס 327
שאלה
How does heating shift an endothermic forward reaction?
תשובה
Toward products, and K increases because temperature changes the equilibrium constant.
כרטיס 328
שאלה
Why do both forward and reverse rates change as equilibrium is approached?
תשובה
As reactant and product concentrations change, the collision frequencies for the two directions change until their rates match.
כרטיס 329
שאלה
CaF₂ has Ksp = 3.2 × 10^-11. What is its molar solubility in 0.10 M NaF?
תשובה
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.
כרטיס 330
שאלה
What concentration data must be used to calculate Kc?
תשובה
Equilibrium concentrations, each raised to its stoichiometric coefficient and excluding pure solids and liquids.
כרטיס 331
שאלה
What is a Brønsted–Lowry acid?
תשובה
A proton donor.
כרטיס 332
שאלה
How is pH defined?
תשובה
pH = -log[H₃O⁺].
כרטיס 333
שאלה
What is Ka for HA + H₂O ⇌ H₃O⁺ + A⁻?
תשובה
Ka = [H₃O⁺][A⁻]/[HA].
כרטיס 334
שאלה
How does stabilizing a base affect its basicity and the strength of its conjugate acid?
תשובה
It makes the base weaker and its conjugate acid stronger. A more stable base is less willing to accept H⁺.
כרטיס 335
שאלה
What is a Brønsted–Lowry base?
תשובה
A proton acceptor.
כרטיס 336
שאלה
At 25°C, what are Kw and the relationship between pH and pOH?
תשובה
Kw = [H₃O⁺][OH⁻] = 1.0 × 10^-14. Taking negative logarithms gives pH + pOH = 14.00.
כרטיס 337
שאלה
What is Kb for B + H₂O ⇌ BH⁺ + OH⁻?
תשובה
Kb = [BH⁺][OH⁻]/[B].
כרטיס 338
שאלה
Why can lowering pH increase the solubility of a salt containing a basic anion?
תשובה
H₃O⁺ consumes the anion, pulling the dissolution equilibrium toward more dissolved ions.
כרטיס 339
שאלה
What are conjugate acid–base pairs?
תשובה
Species that differ by exactly one proton.
כרטיס 340
שאלה
What is the pH of 1.0 × 10^-3 M HCl?
תשובה
3.00, assuming complete dissociation and negligible water contribution.
כרטיס 341
שאלה
How are pKa and pKb defined?
תשובה
pKa = -log Ka, and pKb = -log Kb.
כרטיס 342
שאלה
Why does acid strength increase across a row of comparable hydrides?
תשובה
Increasing electronegativity stabilizes the conjugate base and polarizes the H–A bond.
כרטיס 343
שאלה
What is an amphiprotic species?
תשובה
A species that can donate or accept a proton, such as HCO₃⁻.
כרטיס 344
שאלה
What amounts remain after a limited amount of strong base partially neutralizes weak acid HA?
תשובה
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.
כרטיס 345
שאלה
How are Ka, Kb, pKa, and pKb related for a conjugate pair at 25°C?
תשובה
KaKb = Kw = 1.0 × 10^-14, and pKa + pKb = pKw = 14.00.
כרטיס 346
שאלה
When does pH have little effect on a salt's solubility?
תשובה
When neither dissolved ion reacts appreciably with H₃O⁺ or OH⁻.
כרטיס 347
שאלה
How does H₂O act in HCl + H₂O → H₃O⁺ + Cl⁻ and in NH₃ + H₂O ⇌ NH₄⁺ + OH⁻?
תשובה
It acts as a base in the first reaction by accepting H⁺, and as an acid in the second by donating H⁺.
כרטיס 348
שאלה
After mixing weak base B with strong acid, what controls the final solution in the three stoichiometric regimes?
תשובה
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⁺.
כרטיס 349
שאלה
What two components make a typical weak-acid buffer?
תשובה
A weak acid and a significant amount of its conjugate base.
כרטיס 350
שאלה
What do the successive half-equivalence pH values approximate in a diprotic weak-acid titration?
תשובה
The first approximates pKa₁ and the second approximates pKa₂ because each conjugate pair has equal concentrations at its half-equivalence point.
כרטיס 351
שאלה
Which acid is stronger, one with pKa 2 or pKa 5?
תשובה
The acid with pKa 2; lower pKa means larger Ka.
כרטיס 352
שאלה
What is the Henderson–Hasselbalch equation?
תשובה
pH = pKa + log([A⁻]/[HA]).
כרטיס 353
שאלה
Why are larger binary hydrides down a group often stronger acids?
תשובה
The H–A bond becomes weaker as the central atom grows, so proton release is easier.
כרטיס 354
שאלה
What mainly determines buffer capacity?
תשובה
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.
כרטיס 355
שאלה
Why does acid increase CaCO₃ solubility?
תשובה
H₃O⁺ converts CO₃²⁻ to HCO₃⁻ or carbonic acid species, reducing free carbonate and driving more CaCO₃ to dissolve.
כרטיס 356
שאלה
What does pH < pKa imply for a weak-acid pair?
תשובה
The protonated form HA predominates over A⁻.
כרטיס 357
שאלה
What happens when stoichiometrically equal amounts of a monoprotic weak acid and strong base are mixed?
תשובה
The weak acid is consumed to its conjugate base; at equivalence, the solution isn't a buffer containing both forms.
כרטיס 358
שאלה
What is [H₃O⁺] when pH = 4.50?
תשובה
3.2 × 10^-5 M, from [H₃O⁺] = 10^-pH.
כרטיס 359
שאלה
What is the pH of 0.010 M Ba(OH)₂ at 25°C?
תשובה
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.
כרטיס 360
שאלה
How does a buffer respond to a small amount of added strong acid?
תשובה
Its conjugate base consumes H⁺, converting to the weak acid and limiting the pH change.
כרטיס 361
שאלה
Why is the equivalence-point solution basic in a monoprotic weak-acid–strong-base titration?
תשובה
The conjugate base produced at equivalence reacts with water to form OH⁻, so the pH is above neutral—above 7.00 at 25°C.
כרטיס 362
שאלה
How is percent ionization calculated for a weak acid or weak base?
תשובה
For HA, use ([H₃O⁺]equilibrium ÷ [HA]initial) × 100%. For B, use ([BH⁺]equilibrium ÷ [B]initial) × 100%, under the usual monoprotic setup.
כרטיס 363
שאלה
When is Henderson–Hasselbalch useful for an initial buffer-pH calculation?
תשובה
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.
כרטיס 364
שאלה
Why does adding oxygen atoms usually strengthen oxyacids with the same central atom?
תשובה
Extra oxygens withdraw electron density and delocalize negative charge in the conjugate base.
כרטיס 365
שאלה
A prepared buffer is accidentally diluted to twice its intended volume; what happens to its pH and capacity?
תשובה
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.
כרטיס 366
שאלה
How does adding OH⁻ affect Mg(OH)₂ solubility?
תשובה
It decreases solubility through the common-ion effect, shifting Mg(OH)₂(s) ⇌ Mg²⁺ + 2OH⁻ toward the solid.
כרטיס 367
שאלה
A buffer has equal [A⁻] and [HA]; what is its pH?
תשובה
pH = pKa because log(1) = 0.
כרטיס 368
שאלה
How should a weak acid–strong base mixture be solved before equivalence?
תשובה
First use mole stoichiometry; if both HA and A⁻ remain, use the resulting buffer relation.
כרטיס 369
שאלה
Why can pure neutral water have a pH other than 7.00?
תשובה
Kw changes with temperature. Neutrality means [H₃O⁺] = [OH⁻], while pH = 7.00 only when Kw = 1.0 × 10^-14 at 25°C.
כרטיס 370
שאלה
25.0 mL of 0.200 M HCl is diluted to 100.0 mL; what is the pH?
תשובה
1.301. Dilution gives [H₃O⁺] = (0.200 M)(25.0 mL)/(100.0 mL) = 0.0500 M, so pH = -log(0.0500).
כרטיס 371
שאלה
How does a buffer respond to a small amount of added strong base?
תשובה
The weak acid consumes OH⁻, forming conjugate base and water.
כרטיס 372
שאלה
How do you find the final pH after mixing a strong acid and strong base at 25°C?
תשובה
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.
כרטיס 373
שאלה
What distinguishes acid strength from acid concentration?
תשובה
Strength is the equilibrium tendency to donate H⁺, reflected by Ka or pKa; concentration is the amount of acid per solution volume.
כרטיס 374
שאלה
If [A⁻]/[HA] = 10, how does pH compare with pKa?
תשובה
pH = pKa + 1 because log 10 = 1.
כרטיס 375
שאלה
Which conjugate base is more stable, one with localized or resonance-delocalized charge?
תשובה
The resonance-delocalized conjugate base, which generally corresponds to the stronger acid.
כרטיס 376
שאלה
Which 1.0 L buffer has greater capacity: 1.0 mol each of HA/A⁻ or 0.10 mol each at the same ratio?
תשובה
The 1.0 mol pair; both have the same initial pH, but the larger amounts neutralize more added acid or base.
כרטיס 377
שאלה
For BHX(s) ⇌ BH⁺ + X⁻, why can raising pH increase the salt's solubility?
תשובה
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.
כרטיס 378
שאלה
What does pH > pKa imply for a weak-acid pair?
תשובה
The deprotonated form A⁻ predominates over HA.
כרטיס 379
שאלה
For HA + B ⇌ A⁻ + BH⁺, which side is favored when pKa(HA) = 4 and pKa(BH⁺) = 9?
תשובה
Products are favored. Proton transfer moves toward the weaker acid–base pair, and K ≈ 10^(9 − 4) = 10^5.
כרטיס 380
שאלה
What is the pOH when [OH⁻] = 2.5 × 10^-4 M?
תשובה
3.60, from -log(2.5 × 10^-4).
כרטיס 381
שאלה
What is the pH of 0.100 M HA when Ka = 1.0 × 10^-5?
תשובה
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.
כרטיס 382
שאלה
Why does a buffer fail after too much strong acid is added?
תשובה
Its conjugate base is depleted, so added H⁺ is no longer consumed effectively.
כרטיס 383
שאלה
What do two clear equivalence regions on an acid titration curve suggest?
תשובה
At least two distinguishable titratable protons; on a clean ideal curve with exactly two equivalence regions, this is consistent with a diprotic acid.
כרטיס 384
שאלה
A buffer has pKa 4.8 and [A⁻]/[HA] = 0.10; what is pH?
תשובה
3.8, from 4.8 + log(0.10).
כרטיס 385
שאלה
Why is HCl stronger than HF in water despite F being more electronegative?
תשובה
The H–F bond is much stronger; bond strength dominates this down-group binary-acid comparison.
כרטיס 386
שאלה
Why does percent ionization increase when a weak acid is diluted?
תשובה
Dilution shifts ionization toward more particles, so a larger fraction ionizes even though [H₃O⁺] decreases.
כרטיס 387
שאלה
A buffer contains more HA than A⁻. Which addition can it neutralize in greater amount: strong acid or strong base?
תשובה
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.
כרטיס 388
שאלה
Why can removing a basic anion increase a salt's molar solubility without changing Ksp?
תשובה
The equilibrium shifts to replace the consumed ion; Ksp remains fixed at the same temperature.
כרטיס 389
שאלה
Why can an acid–base indicator change color as pH changes?
תשובה
Its protonated and deprotonated forms have different colors or other observable properties, and their relative amounts change with pH.
כרטיס 390
שאלה
What buffer results from mixing 1.0 mol HA with 0.40 mol OH⁻?
תשובה
0.60 mol HA and 0.40 mol A⁻ remain, forming a buffer before any equilibrium calculation.
כרטיס 391
שאלה
What is the pH of 0.200 M weak base B when Kb = 2.0 × 10^-5 at 25°C?
תשובה
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.
כרטיס 392
שאלה
Why does a weak acid alone not make an effective buffer?
תשובה
It lacks a substantial conjugate-base reserve to consume added strong acid.
כרטיס 393
שאלה
What controls pH after excess strong base passes equivalence?
תשובה
The concentration of excess OH⁻ after accounting for reaction stoichiometry and total volume.
כרטיס 394
שאלה
How should an indicator be chosen for a titration?
תשובה
Its color-change range should fall within the steep pH change near the equivalence point.
כרטיס 395
שאלה
How can a measured pH and known pKa give a conjugate-base/acid ratio?
תשובה
Rearrange Henderson–Hasselbalch: [A⁻]/[HA] = 10^(pH − pKa).
כרטיס 396
שאלה
Can a weak base and its conjugate acid form a buffer?
תשובה
Yes, when both are present in significant amounts.
כרטיס 397
שאלה
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?
תשובה
The concentrated buffer changes pH less because it has greater capacity.
כרטיס 398
שאלה
How does equivalence-point pH compare for strong acid–strong base, weak acid–strong base, and weak base–strong acid titrations at 25°C?
תשובה
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.
כרטיס 399
שאלה
Why should mole ratios replace concentration ratios after mixing buffer solutions?
תשובה
Both components share the same final volume, so that volume cancels in [A⁻]/[HA].
כרטיס 400
שאלה
How does adding a little strong acid change a buffer's conjugate-base and conjugate-acid amounts?
תשובה
The conjugate base decreases and its conjugate acid increases by the amount of strong acid consumed.
כרטיס 401
שאלה
What does entropy measure qualitatively?
תשובה
The dispersal of matter and energy among available microstates.
כרטיס 402
שאלה
How is standard reaction entropy calculated?
תשובה
ΔS°rxn = ΣνS°(products) − ΣνS°(reactants).
כרטיס 403
שאלה
What equation gives ΔG° from ΔH° and ΔS°, and what standard states do the degree symbols assume?
תשובה
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.
כרטיס 404
שאלה
Does thermodynamic favorability guarantee a fast reaction?
תשובה
No. A favorable reaction can be slow when its activation barrier is large.
כרטיס 405
שאלה
What is ΔG at equilibrium?
תשובה
Zero under the current conditions because there is no net driving force.
כרטיס 406
שאלה
Why can an endothermic dissolution still be thermodynamically favorable?
תשובה
A sufficiently positive entropy change can make TΔS exceed positive ΔH, giving negative ΔG.
כרטיס 407
שאלה
How can an unfavorable reaction be driven by a favorable one?
תשובה
Couple them so their equations and ΔG values add to a negative overall ΔG.
כרטיס 408
שאלה
Where does oxidation occur in every electrochemical cell?
תשובה
At the anode.
כרטיס 409
שאלה
How are standard cell potential and standard free energy related?
תשובה
ΔG° = -nFE°cell.
כרטיס 410
שאלה
What equation gives cell potential under nonstandard conditions?
תשובה
E = E° − (RT/nF) ln Q. When Q = 1, ln Q = 0, so E = E°.
כרטיס 411
שאלה
How is electrical charge related to current and time?
תשובה
q = It.
כרטיס 412
שאלה
Which phase has greater molar entropy, liquid water or ice at the same temperature?
תשובה
Liquid water because its molecules have more accessible arrangements and motion.
כרטיס 413
שאלה
Do elements in their standard states have zero standard molar entropy?
תשובה
No. Their ΔHf° is zero, but their absolute S° values are positive above 0 K.
כרטיס 414
שאלה
How do the four ΔH° and ΔS° sign combinations determine thermodynamic favorability across temperature?
תשובה
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.
כרטיס 415
שאלה
What does it indicate when a thermodynamically favored process does not occur at a measurable rate?
תשובה
It is under kinetic control, commonly because of a high activation energy; no measurable reaction does not mean the system is at equilibrium.
כרטיס 416
שאלה
How are ΔG° and K related?
תשובה
ΔG° = -RT ln K.
כרטיס 417
שאלה
What two contributions compete in dissolving an ionic solid?
תשובה
Enthalpy changes from separating and solvating particles, and entropy changes from their new dispersal and solvent organization.
כרטיס 418
שאלה
What must cancel when coupled reactions are added?
תשובה
Shared intermediates, leaving the desired net reaction.
כרטיס 419
שאלה
Where does reduction occur in every electrochemical cell?
תשובה
At the cathode.
כרטיס 420
שאלה
What sign of E°cell indicates a favorable standard galvanic reaction?
תשובה
Positive E°cell, corresponding to negative ΔG°.
כרטיס 421
שאלה
If Q increases for a galvanic reaction, how does E change at fixed temperature?
תשובה
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.
כרטיס 422
שאלה
How are moles of electrons found from charge?
תשובה
Moles e⁻ = q/F, where F ≈ 96485 C mol^-1 e⁻.
כרטיס 423
שאלה
How does producing more gas particles usually affect system entropy?
תשובה
It increases entropy because the particles have more positional microstates.
כרטיס 424
שאלה
Can a dissolution with negative ΔH be unfavorable?
תשובה
Yes. A sufficiently negative entropy change at the stated temperature can make ΔG positive.
כרטיס 425
שאלה
When can a process with ΔH > 0 and ΔS > 0 become favorable?
תשובה
At sufficiently high temperature, when TΔS exceeds ΔH.
כרטיס 426
שאלה
How does a catalyst affect ΔG?
תשובה
It does not change ΔG; it lowers the activation barrier for both directions.
כרטיס 427
שאלה
For A → B, ΔGf°(A) = -50 kJ mol^-1 and ΔGf°(B) = -80 kJ mol^-1. What is ΔG°rxn?
תשובה
-30 kJ mol^-1. Use ΣνΔGf°(products) − ΣνΔGf°(reactants) = -80 − (-50).
כרטיס 428
שאלה
Why can dissolving a gas in a liquid have a negative entropy change?
תשובה
Gas particles lose much of their translational freedom when confined and solvated in the liquid.
כרטיס 429
שאלה
If coupled steps have ΔG values +20 kJ and -35 kJ, what is overall ΔG?
תשובה
-15 kJ, so the combined process is thermodynamically favorable under those conditions.
כרטיס 430
שאלה
What role does each half-cell solution play in an electrochemical cell?
תשובה
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.
כרטיס 431
שאלה
How is E°cell found from standard reduction potentials?
תשובה
E°cell = E°cathode − E°anode, using both tabulated values as reductions.
כרטיס 432
שאלה
How does a cell's potential magnitude change as Q approaches or moves away from K, and what is E at equilibrium?
תשובה
|E| falls toward zero as Q approaches K and grows as the system moves farther from equilibrium. At equilibrium, Q = K and E = 0.
כרטיס 433
שאלה
How many moles of electrons pass when 1.93 × 10^5 C flows?
תשובה
2.00 mol e⁻, from q/F.
כרטיס 434
שאלה
How does a salt bridge maintain charge balance in a galvanic cell?
תשובה
Anions migrate toward the anode compartment and cations toward the cathode compartment, countering the net charge imbalances created by the two half-reactions.
כרטיס 435
שאלה
Why does raising a substance's temperature generally increase its entropy?
תשובה
Energy spreads across more accessible particle energy states, increasing the number of possible microscopic arrangements.
כרטיס 436
שאלה
When can a process with ΔH < 0 and ΔS < 0 be favorable?
תשובה
At sufficiently low temperature, where the unfavorable -TΔS term is small.
כרטיס 437
שאלה
Why can diamond persist even though graphite is more stable at standard conditions?
תשובה
Conversion has a large activation barrier, so diamond is kinetically persistent.
כרטיס 438
שאלה
What do the external circuit and measuring device do in an electrochemical cell?
תשובה
The circuit carries electrons from anode to cathode; a voltmeter measures potential difference, while an ammeter in series measures current.
כרטיס 439
שאלה
At constant temperature, how does increasing the volume available to a gas affect its entropy?
תשובה
Entropy increases because the gas particles can occupy more positions in the larger space, so more microstates are accessible.
כרטיס 440
שאלה
How does reversing one coupled reaction affect its ΔG?
תשובה
It reverses the sign of that reaction's ΔG.
כרטיס 441
שאלה
Why is n required in ΔG° = -nFE°?
תשובה
It is the moles of electrons transferred per balanced reaction, linking charge flow to reaction extent.
כרטיס 442
שאלה
What makes an electrolytic cell operate?
תשובה
An external power source drives a thermodynamically unfavorable redox reaction; oxidation still occurs at the anode and reduction at the cathode.
כרטיס 443
שאלה
In an Mⁿ⁺/M concentration cell, which half-cell is the anode: the dilute or concentrated ion solution?
תשובה
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.
כרטיס 444
שאלה
How is deposited metal mass found from current and time?
תשובה
Find q = It, convert q/F to moles e⁻, use the half-reaction ratio to moles metal, then multiply by molar mass.
כרטיס 445
שאלה
Given product S° total 500 J mol^-1 K^-1 and reactant total 420 J mol^-1 K^-1, what is ΔS°?
תשובה
+80 J mol^-1 K^-1.
כרטיס 446
שאלה
How do electrode masses change in a Zn–Cu galvanic cell?
תשובה
The Zn anode loses mass as Zn → Zn²⁺ + 2e⁻, while the Cu cathode gains mass as Cu²⁺ + 2e⁻ → Cu.
כרטיס 447
שאלה
What is ΔG° when ΔH° = 50 kJ mol^-1, ΔS° = 0.200 kJ mol^-1 K^-1, and T = 300 K?
תשובה
-10 kJ mol^-1, from ΔG° = 50 − (300)(0.200).
כרטיס 448
שאלה
Why can temperature change a solid's solubility?
תשובה
Temperature changes the balance of ΔH and TΔS, so it changes the free energy of dissolution and the equilibrium constant.
כרטיס 449
שאלה
What does the size of ΔG° relative to RT imply about K?
תשובה
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.
כרטיס 450
שאלה
Bubbles form at an inert cathode in acidic solution; which half-reaction can explain them?
תשובה
2H⁺ + 2e⁻ → H₂(g). Gas evolution at the cathode can be direct evidence of reduction.
450 כרטיסים
AP Chemistry Flashcards: Complete 9-Unit Course Review
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