AS & A Level Chemistry 9701 · Topic 26

Reaction kinetics: past paper questions

6 real questionsasked in 2 of the last 10 exam series2023–2023usually: Suggest, Identify, Complete, Use, Explain

Real questions on reaction kinetics

The newest 5 of 5 written questions, plus 1 multiple-choice. Open one to see it on the real paper.

9701/41 · October/November 2023 · Q1a(i)[2]
Suggest a two-step mechanism for this reaction. step 1 step 2
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9701/41 · October/November 2023 · Q1a(ii)[1]
Identify the rate-determining step in this mechanism. Explain your answer.
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9701/41 · October/November 2023 · Q1b(i)[1]
Complete the rate equation for this reaction, stating the overall order of the reaction. rate = overall order of reaction =
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9701/41 · October/November 2023 · Q1b(ii)[1]
Use your rate equation in (i) to calculate the rate of the reaction when the concentrations of F 2 and Cl O 2 are both 2.00 × 10 −3 mol dm −3 . rate = mol dm −3 s −1
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9701/43 · May/June 2023 · Q5a(ii)[1]
Explain what is meant by a heterogeneous catalyst.
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What examiners said

This question was well answered. Candidates had to suggest two equations for this mechanism that was consistent with the given information. Common errors included: • step 1 not being a molar ratio (1:1) consistent with the orders of reaction, • steps in the mechanism that were not balanced.
— Examiner report, October/November 2023, 9701/41 Q1(a)(i) (Cambridge)

This proved difficult for some candidates. Answers should be linked to the rate determining step (step 1) which contains one mole of F2 and one mole of ClO2.
— Examiner report, October/November 2023, 9701/41 Q1(a)(ii) (Cambridge)

Most candidates gave the correct rate equation. A common error was to square the concentration of ClO2.
— Examiner report, October/November 2023, 9701/41 Q1(b)(i) (Cambridge)

Practise this topic

Answer these questions online and get each one marked against the official mark scheme, with what you missed and how to fix it.

Practise reaction kinetics

In the syllabus

26.1 Simple rate equations, orders of reaction and rate constants

explain and use the terms rate equation, order of reaction, overall order of reaction, rate constant,
(a) understand and use rate equations of the form rate = k [A]m[B]n (for which m and n are 0, 1 or 2)
deduce the order of a reaction from concentration–time graphs or from experimental data relating to
interpret experimental data in graphical form, including concentration–time and rate–concentration
(a) show understanding that the half-life of a first-order reaction is independent of concentration
calculate the numerical value of a rate constant, for example by:
for a multi-step reaction:
suggest a reaction mechanism that is consistent with the rate equation and the equation for the
deduce a rate equation using a given reaction mechanism and rate-determining step for a given
describe qualitatively the effect of temperature change on the rate constant and hence the rate of a

26.2 Homogeneous and heterogeneous catalysts

explain that catalysts can be homogeneous or heterogeneous
describe the mode of action of a heterogeneous catalyst to include adsorption of reactants, bond
palladium, platinum and rhodium in the catalytic removal of oxides of nitrogen from the exhaust
describe the mode of action of a homogeneous catalyst by being used in one step and reformed in a

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