Physical Chemistry: A Level Chemistry questions and answers
10 free A Level Chemistry Physical Chemistry questions written in the style of Cambridge Chemistry papers, each with its answer and mark scheme. 4 of them are A* challenge questions, built to catch the mistakes strong students still make.
This topic covers Lattice energy, Born–Haber & entropy, Electrochemistry, Acid–base & solubility equilibria, Reaction kinetics. Work through the questions below, then generate a full Physical Chemistry paper with a fresh set every time.
Calculate the pH of a 0.200 mol dm−3 solution of HA. State one assumption.
[3]
(b)
A buffer contains 0.02 mol HA and 0.015 mol NaA in 1.00 dm3. Calculate its pH, and explain how it resists a change in pH when a small amount of acid is added.
[5]
(c)
A sparingly soluble salt MX has Ksp = 5.0 × 10−13 mol2 dm−6. Calculate its solubility in water and in 0.10 mol dm−3 NaX.
[3]
Show answers and mark scheme
Part
Answer and marking points
Marks
(a)
2.45; [H+] = [A−] and dissociation is negligible
[H+] = √(Kac) C1 2.45 A1 assumption stated B1
3
(b)
4.08; A− + H+ → HA, large reservoir of A−
[H+] = Ka[HA]/[A−] C1 4.08 A1 added H+ removed by A−B1 equation A− + H+ → HA B1 ratio [HA]/[A−] changes little B1
5
(c)
7.07 × 10−7, 5.00 × 10−12
s = √KspC1 7.07 × 10−7A1 common ion: s = Ksp ÷ 0.10 = 5.00 × 10−12A1
3
Question 2Structured · 4 marksA* challenge
The half-life of a first-order reaction is constant.
(a)
Explain how a concentration–time graph shows that a reaction is first order.
[2]
(b)
A first-order reaction has a half-life of 45 s. Calculate the rate constant.
[2]
Show answers and mark scheme
Part
Answer and marking points
Marks
(a)
constant half-life
successive half-lives are equal B2
2
(b)
0.0154 s⁻¹
k = ln 2 / t½C1 0.0154 s−1A1
2
Question 3Structured · 3 marksA* challenge
Solubility product applies to sparingly soluble salts.
(a)
Write the Ksp expression for calcium fluoride, CaF₂.
[1]
(b)
Explain the common ion effect when sodium fluoride is added to a saturated CaF₂ solution.
[2]
Show answers and mark scheme
Part
Answer and marking points
Marks
(a)
Ksp = [Ca²⁺][F⁻]²
Ksp = [Ca²⁺][F⁻]2B1
1
(b)
equilibrium shifts left; precipitate
[F⁻] increases B1 equilibrium shifts to form more CaF₂ precipitate B1
2
Question 4Structured · 4 marksA* challenge
Entropy and Gibbs free energy determine feasibility.
(a)
Explain why the entropy increases when a solid dissolves.
[2]
(b)
For a reaction ΔH = +178 kJ mol−1 and ΔS = +161 J K−1 mol−1. Calculate the minimum temperature for the reaction to be feasible.
[2]
Show answers and mark scheme
Part
Answer and marking points
Marks
(a)
more disorder, more ways to arrange
particles become more dispersed/disordered B1 more ways of arranging energy B1
2
(b)
1106 K
T = ΔH/ΔS = 178 000/161 C1 1106 K A1
2
Question 5Structured · 3 marks
A current of 2.2 A is passed through aqueous copper(II) sulfate for 48 minutes. Calculate the mass of copper deposited. (F = 96 500 C mol−1, Ar Cu = 63.5)
[3]
Show answers and mark scheme
Part
Answer and marking points
Marks
2.08 g
Q = It C1 mol e− ÷ 2 C1 2.08 A1
3
Question 6Structured · 9 marks
Dinitrogen pentoxide decomposes at 338 K: 2N₂O₅(g) → 4NO₂(g) + O₂(g). Fig. 6.1 shows how its concentration changes with time.
Fig. 6.1
(a)
Use Fig. 6.1 to determine two successive half-lives, and show that the reaction is first order with respect to N₂O₅.
[3]
(b)
Use your answer to (a) to calculate the rate constant, k, with units.
[2]
(c)
Calculate the initial rate of decrease of [N₂O₅].
[1]
(d)
Explain, in terms of the Boltzmann distribution, why a small rise in temperature greatly increases the rate.
[2]
(e)
Suggest a practical method for following the concentration of NO₂ during the reaction.
[1]
Show answers and mark scheme
Part
Answer and marking points
Marks
(a)
both about 86.6 s; constant half-life
first half-life 86.6 s (± 10 s) B1 second half-life the same (± 10 s) B1 constant half-life shows first order B1
more molecules with E ≥ Ea; more successful collisions
the distribution shifts so a much larger fraction of molecules have energy ≥ EaB1 so the frequency of successful collisions increases greatly B1
2
(e)
colorimetry (NO₂ brown)
colorimetry, since NO₂ is brown (absorbance proportional to concentration) B1
1
Question 7Structured · 4 marks
The rate equation for a reaction is rate = k[A][B]2.
(a)
State the order with respect to each reactant and the overall order.
[2]
(b)
Deduce the units of k.
[1]
(c)
State the effect on the rate of doubling [B] and halving [A].
[1]
Show answers and mark scheme
Part
Answer and marking points
Marks
(a)
1, 2, 3
first order in A, second order in B B1 overall third order B1
2
(b)
dm⁶ mol⁻² s⁻¹
dm6 mol−2 s−1B1
1
(c)
×2
rate doubles B1
1
Question 8Structured · 11 marks
This question is about the enthalpy change of solution of CaCl₂. Lattice energy = −2258 kJ mol−1; enthalpy change of hydration of Ca²⁺ = −1579 kJ mol−1; of Cl⁻ = −378 kJ mol−1.
(a)
Define enthalpy change of hydration.
[2]
(b)
Construct an energy cycle and calculate the enthalpy change of solution.
[3]
(c)
Explain why the enthalpy change of hydration of Mg²⁺ is more exothermic than that of Ca²⁺.
[2]
(d)
Define entropy and predict the sign of the entropy change when a solid ionic compound dissolves.
[2]
(e)
Explain how a salt with an endothermic enthalpy of solution can still be soluble at room temperature.
[2]
Show answers and mark scheme
Part
Answer and marking points
Marks
(a)
enthalpy change when 1 mol of gaseous ions dissolves in water to give infinitely dilute solution
enthalpy change when one mole of gaseous ions B1 is dissolved in a large excess of water (infinitely dilute solution) B1
Mg²⁺ smaller, higher charge density; stronger ion–dipole attraction to water
Mg²⁺ has a smaller ionic radius (same charge) so a higher charge density B1 it attracts the δ− oxygen of water molecules more strongly B1
2
(d)
measure of disorder / number of ways of arranging; usually positive
entropy is a measure of the number of ways particles and energy can be arranged (disorder) B1 usually positive because ions are freed from the lattice B1
2
(e)
ΔS positive enough that ΔG = ΔH − TΔS negative
dissolving can be feasible if ΔG = ΔH − TΔS < 0 B1 a large positive ΔS makes −TΔS outweigh the positive ΔH B1
2
Question 9Structured · 9 marks
The solubility product of Ag₂CrO₄ is 1.10 × 10−12 mol3 dm−9 at 298 K.
(a)
Write the expression for Ksp of this salt.
[1]
(b)
Calculate the solubility of the salt in mol dm−3.
[3]
(c)
Explain the common ion effect and predict how solubility changes in a solution already containing the anion at 0.10 mol dm−3.
[3]
(d)
State whether a precipitate forms when equal volumes of solutions containing 2.0 × 10−3 mol dm−3 of each ion are mixed. Explain.
added common ion shifts equilibrium to solid; solubility much lower
the equilibrium salt(s) ⇌ ions shifts towards the solid when one of its ions is already present B1 solubility decreases greatly B1 Ksp unchanged B1
3
(d)
compare ionic product after dilution with Ksp
concentrations halve on mixing B1 ionic product calculated and compared with Ksp: precipitate if ionic product exceeds KspB1
2
Question 10Structured · 11 marks
The initial rate of the reaction A + B → products was measured for different starting concentrations.
experiment
[A] / mol dm−3
[B] / mol dm−3
initial rate / mol dm−3 s−1
1
0.010
0.010
2.00 × 10−7
2
0.020
0.010
4.00 × 10−7
3
0.010
0.020
4.00 × 10−7
Table 10.1
(a)
Define the order of reaction with respect to a reactant.
[1]
(b)
Use the data to deduce the order with respect to A and to B. Explain your reasoning.
[3]
(c)
Write the rate equation and calculate the rate constant, with units.
[3]
(d)
The reaction of a different compound is first order. Its half-life is 25 s. Calculate the rate constant and state how the half-life changes if the initial concentration is doubled.
[3]
(e)
Explain how the rate constant changes with temperature.
[1]
Show answers and mark scheme
Part
Answer and marking points
Marks
(a)
power of its concentration in the rate equation
the power to which the concentration of that reactant is raised in the rate equation B1
1
(b)
A: 1; B: 1
A: doubling [A] multiplies rate by 2 so order 1 B1 B: doubling [B] multiplies rate by 2 so order 1 B1 reasoning shown B1
3
(c)
2.00 × 10−3 mol−1 dm3 s−1
rate = k[A][B] B1 k = 2.00 × 10−3M1 units mol−1 dm3 s−1A1
3
(d)
0.0277 s⁻¹; unchanged
k = ln 2 / t½M1 0.0277 s−1A1 half-life unchanged (constant for first order) B1
3
(e)
increases: more molecules exceed Ea
k increases with temperature as a greater proportion of molecules have energy ≥ EaB1
In the 9701 syllabus, Physical Chemistry covers Lattice energy, Born–Haber & entropy, Electrochemistry, Acid–base & solubility equilibria, Reaction kinetics.
Where can I get Physical Chemistry questions with mark schemes?
This page has 10 Physical Chemistry questions with answers. For more, the free generator on mentorriyaz.in builds a new Physical Chemistry paper with a full mark scheme each time you click.
Want a mentor, not just a paper?
Riyaz Shaikh has mentored IGCSE, IB and A Level students for 15+ years, one-on-one, online and in Mumbai. The hardest questions on this site are the ones he uses to find a student's weak points.
Original Cambridge-style practice questions written for mentorriyaz.in. These are not Cambridge past paper questions, and this site is not affiliated with or endorsed by Cambridge University Press & Assessment. Updated 2026-11-04. Paper generator · mentorriyaz.in