Effect of temperature on reaction rates and the concept of activation energy: past paper questions

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• Question 14May/June 2026, paper 11Multiple choice1 mark

  Nitrogen and hydrogen react to form ammonia in a reversible reaction. $${\text{N}}_2+3{\text{H}}_2\rightleftharpoons 2{\text{NH}}_3\mathrm{\Delta }H=-92{\text{ kJ mol}}^{-1}$$

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• Question 15Oct/Nov 2025, paper 12Multiple choice1 markHas a diagram

  Which reaction pathway diagram shows an endothermic reaction that occurs in two steps and in which the second step of the reaction is likely to be faster than the first?

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• Question 15Oct/Nov 2024, paper 11Multiple choice1 markHas a diagram

  The diagram shows a Boltzmann distribution curve. The axes are not labelled. Points X and Y are points on the vertical axis.

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• Question 15Oct/Nov 2023, paper 11Multiple choice1 mark

  The forward reaction of a reversible reaction is exothermic and has an activation energy of $+30{\text{ kJ mol}}^{-1}$. The reverse reaction proceeds by a mechanism that is the exact reverse of the mechanism of the forward reaction.

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• Question 15May/June 2026, paper 11Multiple choice1 markHas a diagram

  The diagram shows the Boltzmann distribution of energies in one mole of a gas. The gas takes part in a reaction with an activation energy, $E_{\text{a}}$. Which statement correctly describes the effect of an increase in temperature?

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• Question 15Oct/Nov 2025, paper 13Multiple choice1 mark

  The reversible reaction between methanol and ethanoic acid liquids is catalysed by adding a small volume of concentrated sulfuric acid. Two statements about this reaction are listed. 1 The sulfuric acid is a homogeneous catalyst.

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• Question 16Oct/Nov 2024, paper 12Multiple choice1 markHas a diagram

  The Boltzmann distribution for a mixture of gases capable of reaction is shown. The two curves represent the mixture of gases at ${25}^{\circ }\text{C}$ and at ${35}^{\circ }\text{C}$. The activation energies for the catalysed and uncatalysed reactions are shown.

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• Question 15May/June 2026, paper 12Multiple choice1 markHas a diagram

  The diagram shows a Boltzmann distribution of molecular energies for a gaseous mixture. The distribution has a peak, labelled P. What happens when an effective catalyst is added to the mixture?

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• Question 33May/June 2025, paper 11Multiple choice1 markHas a diagram

  A possible mechanism for the exothermic hydrolysis of 2-chloro-2-methylpropane is shown.

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• Question 15Oct/Nov 2024, paper 13Multiple choice1 markHas a diagram

  The diagram shows a Boltzmann distribution curve. The axes are not labelled. [Diagram: Boltzmann distribution curve with point Y at the peak and point X at energy $E_{\mathrm{A}}$] Points X and Y are points on the vertical axis.

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• Question 15May/June 2023, paper 11Multiple choice1 mark

  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?

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• Question 14May/June 2026, paper 13Multiple choice1 markHas a diagram

  The reaction pathway diagram shows the reaction which occurs when $({\text{CH}}_3{)}_3\text{CCl}$ reacts with ${\text{OH}}^{-}$. Which statements are correct?

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• Question 3May/June 2025, paper 12Multiple choice1 markHas a diagram

  The diagram shows a Boltzmann distribution of molecular energies for a gaseous reaction at two different temperatures and two different activation energies.

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• Question 10May/June 2024, paper 11Multiple choice1 markHas a diagram

  For a certain endothermic reaction, the activation energy is numerically equal to twice the enthalpy change of reaction. Which reaction pathway diagram is correct for this reaction?

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• Question 15May/June 2023, paper 12Multiple choice1 mark

  The equations for two reactions are shown. $$\text{reaction X}2\text{NOBr}\to 2\text{NO}+{\text{Br}}_2$$ $$\text{reaction Y}2\text{NOCl}\to 2\text{NO}+{\text{Cl}}_2$$ The two reactions have similar reaction mechanisms.

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• Question 15May/June 2026, paper 13Multiple choice1 markHas a diagram

  The graph shows a Boltzmann distribution for a sample of reacting gas at a temperature $T\text{ K}$. The activation energy, $E_{\text{A}}$, for the reaction is marked. Point Q is the point of intercept of the curve with the value of the activation energy, $E_{\text{A}}$.

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• Question 13May/June 2025, paper 12Multiple choice1 markHas a diagram

  Under certain conditions, $\mathrm{C}\mathrm{C}{\mathrm{l}}_4$ and ${\mathrm{H}}_2\mathrm{O}$ react as shown. The activation energy for the reaction is $+62{\text{ kJ mol}}^{-1}$.

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• Question 15May/June 2024, paper 11Multiple choice1 markHas a diagram

  The Boltzmann distribution for the hydrogenation of an alkene at a particular temperature in the absence of a catalyst is shown. Which row correctly describes the effects of adding a nickel catalyst to the reaction vessel?

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• Question 16May/June 2023, paper 12Multiple choice1 markHas a diagram

  The diagram shows the Boltzmann distribution of energies in a gas. The gas can take part in a reaction with an activation energy, $E_{\text{a}}$. The gas is maintained at a constant temperature.

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• Question 3May/June 2026, paper 23Structured13 marksHas a diagram

  The conditions used for the conversion of sulfur dioxide to sulfur trioxide in the Contact process are carefully controlled.

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• Question 2May/June 2025, paper 13Multiple choice1 markHas a diagram

  Diagram 1 shows the reaction pathway for a reaction. Diagram 2 shows a graph of concentration of reactant against time for the same reaction. Which diagrams, drawn to the same scale, show the effect of increased temperature on this reaction?

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• Question 13May/June 2024, paper 12Multiple choice1 markHas a diagram

  The volume of ammonia produced against time is measured in two experiments.

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• Question 18May/June 2023, paper 13Multiple choice1 markHas a diagram

  The rate of an exothermic reaction is followed by measuring the concentration of a reactant at regular time intervals. During the experiment the temperature of the reaction mixture is not controlled. Which graph shows the change in concentration of reactant against time?

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• Question 7May/June 2025, paper 13Multiple choice1 markHas a diagram

  The gaseous compound Z decomposes on heating. In the diagram, Boltzmann distributions for Z at two different temperatures, P and Q, are shown. The lines X and Y indicate activation energies for the decomposition of Z with and without a catalyst.

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• Question 15May/June 2024, paper 12Multiple choice1 markHas a diagram

  Gas Q decomposes slowly at room temperature. $$\text{Q(g)}\to \text{X(g)}+\text{Z(g)}$$ The Boltzmann distribution curve for gas Q at room temperature is shown. Which change occurs when a catalyst is added to gas Q?

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• Question 19May/June 2023, paper 13Multiple choice1 mark

  For a particular reversible reaction the backward reaction is endothermic. The activation energy of the backward reaction is $160{\text{ kJ mol}}^{-1}$.

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• Question 3May/June 2025, paper 21Structured10 marksHas a diagram

  Hexene reacts with hydrogen gas to produce hexane.

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• Question 10May/June 2024, paper 13Multiple choice1 markHas a diagram

  In the high temperatures of car engines, nitrogen reacts with oxygen to produce nitrogen monoxide.

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• Question 21May/June 2023, paper 13Multiple choice1 markHas a diagram

  The diagram shows the Boltzmann distribution of the energy of gaseous molecules at a particular temperature. Which statement is correct?

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• Question 3May/June 2025, paper 22Structured16 marksHas a diagram

  ${\text{C}}_3{\text{H}}_6$ reacts with $\text{HBr}(\text{g})$ in an addition reaction. Define addition reaction.

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