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