AS Level Chemistry chapter 8: Reaction kinetics MCQs with answers
By Team Megalecture · Updated 4 Nov 2026
63 exam-style questions on Reaction kinetics, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.
Try each one, then open the answer. These ten stay the same; the test draws new ones every time.
1. A reaction has ΔH = −90 kJ mol−1 and an activation energy for the forward reaction of +60 kJ mol−1. What is the activation energy of the reverse reaction, in kJ mol−1?
A
+30
B
+60
C
+90
D
+150
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Answer: D. The products lie 90 kJ mol−1 below the reactants, and the transition state lies 60 above the reactants, so the reverse barrier is 60 + 90 = 150. +30 subtracts instead of adding.
2. The concentration of a reactant falls from 0.800 mol dm−3 to 0.500 mol dm−3 in 2.0 minutes. What is the average rate of reaction in mol dm−3 s−1?
A
2.5 × 10−3
B
4.2 × 10−3
C
0.15
D
6.7 × 10−3
Show answer
Answer: A. Change in concentration = 0.300 mol dm−3 over 120 s. Rate = 0.300 ÷ 120 = 2.5 × 10−3 mol dm−3 s−1. 0.15 forgets to convert minutes into seconds.
3. The temperature of a reaction mixture is raised. Which of these happen? 1 the frequency of collisions increases 2 the activation energy decreases 3 the proportion of molecules with energy greater than or equal to the activation energy increases
A
1, 2 and 3
B
1 and 3 only
C
1 and 2 only
D
2 and 3 only
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Answer: B. Faster molecules collide more often and a larger proportion have E ≥ EA. The activation energy itself is not changed by temperature; only a catalyst changes the pathway.
4. For a reversible reaction whose forward reaction is exothermic, the temperature is raised. What happens to the rates of the forward and reverse reactions?
A
the forward rate increases and the reverse rate decreases
B
the forward rate decreases and the reverse rate increases
C
both rates decrease
D
both rates increase
Show answer
Answer: D. A rise in temperature increases the rate of every reaction, forward and reverse. The reverse (endothermic) reaction has the larger EA, so its rate increases more, which is why the equilibrium shifts towards the reactants.
5. Two different gas reactions, P and Q, take place at the same temperature. Reaction P has EA = 50 kJ mol−1 and reaction Q has EA = 80 kJ mol−1. What does a Boltzmann distribution show about them?
A
the curve for Q is shifted to higher energy
B
the area beyond EA is larger for Q because more energy is available
C
the area beyond EA is smaller for Q, so a smaller fraction of collisions can be effective
D
the areas beyond EA are equal because the temperature is the same
Show answer
Answer: C. At the same temperature the curve is the same; EA for Q is further along the energy axis, so the area beyond it, and the fraction of molecules able to react, is smaller.
6. For a gas reaction, raising the temperature from 300 K to 310 K increases the fraction of collisions with energy ≥ EA from 1.0 × 10−8 to 2.1 × 10−8, and increases the total collision frequency by 1.7%. By approximately what factor does the rate increase?
A
1.02
B
1.03
C
2.1
D
3.1
Show answer
Answer: C. Rate ∝ collision frequency × fraction effective = 1.017 × 2.1 ≈ 2.1. The greater fraction with E ≥ EA is by far the main effect; 3.1 wrongly adds the two factors.
7. The same amounts of the same reactants are used in two experiments, one at 20 °C and one at 40 °C, and the gas produced is measured at the same temperature and pressure. How does the graph of gas volume against time at 40 °C compare with that at 20 °C?
A
the initial gradient is steeper and the final volume is the same
B
the initial gradient is steeper and the final volume is larger
C
the initial gradient is the same and the final volume is larger
D
the initial gradient is less steep and the final volume is the same
Show answer
Answer: A. Higher temperature gives a faster rate, so a steeper initial gradient, but the amount of limiting reactant is the same, so the same final volume of gas forms.
8. Which statement about the Boltzmann distribution of molecular energies in a gas at constant temperature is correct?
A
the mean energy of the molecules is greater than the most probable energy
B
the peak of the curve shows the mean energy of the molecules
C
exactly half of the molecules have more energy than the most probable energy
D
no molecule has more than twice the most probable energy
Show answer
Answer: A. The curve is skewed, with a long tail at high energy, so the mean lies to the right of the peak (the most probable energy) and more than half of the molecules lie beyond the peak. There is no upper limit to the energy.
9. How does the Boltzmann distribution curve change when the temperature of a gas is raised?
A
the peak moves to higher energy and becomes lower; the area under the curve is unchanged
B
the peak moves to higher energy and becomes taller
C
the curve does not change but EA moves to the left
D
the area under the curve increases because the molecules gain energy
Show answer
Answer: A. The number of molecules is fixed, so the area cannot change. The curve spreads to higher energies, which lowers and flattens the peak and pushes more molecules past EA.
10. Manganese(IV) oxide powder catalyses the decomposition of a fixed volume of hydrogen peroxide solution into water and oxygen. The experiment is repeated with twice the mass of the same powder. What happens?
A
the initial rate increases and the final volume of oxygen is unchanged
B
the initial rate increases and the final volume of oxygen doubles
C
the initial rate is unchanged and the final volume of oxygen doubles
D
the initial rate and the final volume of oxygen are both unchanged
Show answer
Answer: A. More solid catalyst gives more surface for the reaction, so the rate rises. The amount of hydrogen peroxide is unchanged and a catalyst does not alter the amount of product, so the final volume of oxygen is the same.
63, each with the answer and a short explanation, across 3 topics: Rate of reaction, Effect of temperature on reaction rates and the concept of activation energy, Homogeneous and heterogeneous catalysts. Every chapter test draws ten of them, so you can take it many times.
Is the AS Level Chemistry chapter 8 test free?
Yes. The test, the answers and the explanations are free and need no sign-up. Sign in only if you want your scores kept across devices.
How is the chapter test marked?
The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.
