Practise 29 real questions on Reaction kinetics from 2021 to 2026. See the answer and explanation as soon as you answer.
Reaction kinetics is one of the 18 main topics in our A Level Chemistry (Cambridge (CAIE) 9701) question bank, and about 4% of its real questions come from it. Tayyari Karo has 29 real questions on this topic from 2021 to 2026, from Paper 1, Paper 2, Paper 4; 18 are multiple choice and marked instantly, and the rest are structured questions with a model answer. By difficulty: 18 medium, 7 hard, 4 easy.
Work through the questions below, then open the explanation for each one. Redo the ones you missed a few days later.
These are real past-paper questions. Think of your answer first, then open the explanation.
The rate of reaction between a reactive metal and excess dilute acid is investigated. Total volume of H2 gas: 0s=0, 30s=64, 60s=105, 90s=132, 120s=151, 150s=161, 180s=167 cm3. The average rate during the first 30 s is P; the average rate during the last 30 s is Q. What is the value of P − Q?
Answer: B. 1.93 cm3 s⁻¹
P = 64/30 = 2.13 cm3 s⁻¹; Q = (167−161)/30 = 0.20 cm3 s⁻¹; P − Q = 1.93 cm3 s⁻¹.
The reversible reaction between methanol and ethanoic acid liquids is catalysed by adding concentrated sulfuric acid. Statement 1: the sulfuric acid is a homogeneous catalyst. Statement 2: the sulfuric acid lowers the activation energy of the reverse reaction. Which statements are correct?
Answer: A. both 1 and 2
H2SO4 is in the same (liquid) phase as the reactants, so it is a homogeneous catalyst; a catalyst lowers the activation energy of both the forward and reverse reactions.
Iodine and propanone react: I2(aq) + CH3COCH3(aq) → CH3COCH2I(aq) + HI(aq). If the concentration of propanone is increased, keeping the total reaction volume constant, the initial rate of the reaction also increases. What could be the reason for this?
Answer: D. There are more collisions per second between particles at the higher concentration.
Increasing concentration increases the frequency of collisions between particles (not their energy or the proportion that are successful), increasing rate.
The temperature of a sample of an inert gas is increased. What effect does this have on the number of molecules with the most probable energy and on the number of molecules with higher energy?
Answer: B. most probable energy: decreases; higher energy: increases
On the Maxwell-Boltzmann distribution, increasing T flattens and broadens the curve: the peak (number with most probable energy) decreases while the area under the high-energy tail (number with higher energy) increases.
The forward reaction of a reversible reaction is exothermic and has an activation energy of +30 kJ mol⁻1. The reverse reaction proceeds by a mechanism that is the exact reverse of the mechanism of the forward reaction. Which statement about the activation energy of the reverse reaction is correct?
Answer: D. It is greater than +30 kJ mol⁻1.
Ea(reverse) = Ea(forward) − ΔH. Since the forward reaction is exothermic (ΔH negative) and Ea(forward)=+30, Ea(reverse) = 30 + |ΔH| > 30 kJ mol⁻1.
Which statement about catalysts is correct?
Answer: C. They increase the number of particles that have sufficient energy to react.
Catalysts provide an alternative pathway of lower activation energy, so a greater proportion of particles have enough energy to react successfully at a given temperature.
| Session | Paper 1 | Paper 2 | Paper 4 |
|---|---|---|---|
| May/June 2026 | 1 | – | – |
| May/June 2025 | 2 | 1 | 1 |
| October/November 2025 | 1 | – | 1 |
| May/June 2024 | 1 | – | 1 |
| October/November 2024 | 2 | – | – |
| May/June 2023 | 2 | – | 1 |
| October/November 2023 | 2 | 1 | 1 |
| May/June 2022 | 1 | – | 1 |
| October/November 2022 | 2 | – | 1 |
| May/June 2021 | 2 | 1 | 1 |
| October/November 2021 | 2 | – | – |
29 real A Level Chemistry (9701) questions on Reaction kinetics from 2021 to 2026, from Paper 1, Paper 2, Paper 4. Each one shows the year, session and paper it came from.
Yes. Every question shows the correct answer and a short explanation the moment you answer.
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