Free Reaction kinetics questions for AS Level Chemistry (9701), part of Physical chemistry. Each question has the answer and the marking points an examiner would look for.
Generate a full Reaction Kinetics worksheet →All Physical chemistry questionsThe temperature of a gaseous reaction mixture is increased. The Boltzmann distribution curve changes.
Which row is correct?
| height of peak | area under curve | proportion of molecules with E ≥ Ea | |
|---|---|---|---|
| A | lower | unchanged | unchanged |
| B | lower | increases | increases |
| C | higher | unchanged | increases |
| D | lower | unchanged | increases |
Answer: D
A catalyst increases the rate of a reaction.
1 It shifts the Boltzmann distribution to higher energies.
2 It does not change the position of equilibrium.
3 A greater proportion of collisions have energy ≥ Ea.
Which statements are correct?
Answer: B
Which term is described by this statement?
“A substance that increases rate by providing a lower activation energy pathway and is unchanged.”
Answer: C
Define rate of reaction and describe how it can be measured.
Define rate of reaction.
Suggest two methods of following the rate of reaction of marble chips with acid.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | change in concentration per unit time change in concentration of reactant or product per unit time B1 | 1 |
| (b) | gas volume; mass loss measure volume of CO₂ with gas syringe B1 measure loss of mass on a balance B1 | 2 |
This question is about rates of reaction.
Sketch the Boltzmann distribution of molecular energies for a gas at temperature T, and on the same axes the curve at a higher temperature. Label the activation energy, Ea.
Use your sketch to explain why a small increase in temperature causes a large increase in the rate of reaction.
Explain, using the Boltzmann distribution, how a catalyst increases the rate of a reaction.
Distinguish between homogeneous and heterogeneous catalysis, giving one example of each.
Describe how the rate of the reaction between calcium carbonate and hydrochloric acid could be followed, and how the initial rate is found from the results.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | skewed curve from origin; higher T: peak lower and to the right, same area; Ea marked curve starting at the origin, peak, long tail not touching axis B1 higher-T curve with lower peak shifted to higher energy B1 same area under both curves and Ea marked B1 | 3 |
| (b) | many more molecules with energy ≥ Ea; more successful collisions per unit time the number of molecules with energy greater than or equal to Ea increases greatly (area beyond Ea) B1 so the frequency of successful collisions increases B1 | 2 |
| (c) | alternative route with lower Ea; more molecules exceed it provides an alternative reaction pathway with a lower activation energy B1 a greater proportion of molecules have energy above the new Ea B1 | 2 |
| (d) | same phase vs different phase; e.g. H⁺ in esterification / Fe in Haber Any 3 of: homogeneous: catalyst in the same phase as reactants; heterogeneous: different phase; correct example of each (e.g. H₂SO₄ in esterification; Fe in Haber process / Pt in catalytic converter) B3 | 3 |
| (e) | measure mass loss / gas volume against time; plot graph; gradient of tangent at t = 0 measure the loss in mass (or volume of CO₂) at regular time intervals B1 plot mass loss against time B1 draw a tangent at t = 0 and find its gradient B1 | 3 |
Calcium carbonate reacts with hydrochloric acid. 48 cm3 of carbon dioxide, measured at room conditions, is collected in the first 30 s.
Define the term activation energy.
Describe and explain, with reference to the Boltzmann distribution, the effect of increasing temperature on the rate.
Calculate the average rate of production of carbon dioxide in mol s−1.
Explain how a catalyst increases the rate of a reaction.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | minimum energy for a successful collision the minimum energy that colliding particles need in order to react B1 | 1 |
| (b) | peak lower and moves right; more particles with E ≥ Eₐ curve flattens and the peak moves to higher energy M1 more particles have energy ≥ Ea M1 so the frequency of successful collisions increases M1 | 3 |
| (c) | 6.67 × 10−5 mol s−1 n = 48/24 000 = 2.00 × 10−3 mol C1 rate = 6.67 × 10−5 mol s−1 A1 | 2 |
| (d) | alternative route, lower Eₐ provides an alternative route with a lower activation energy M1 so a greater proportion of collisions have energy ≥ Ea M1 | 2 |
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.
Meet Riyaz →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