A LevelChemistryCambridge (CIE)Exam Questions8. Reaction KineticsEffect of Temperature on Reaction Rates & the Concept of Activation Energy

Effect of Temperature on Reaction Rates & the Concept of Activation Energy (Cambridge (CIE) A Level Chemistry): Exam Questions

Exam code: 9701

1 hour20 questions

Select a download format for Effect of Temperature on Reaction Rates & the Concept of Activation Energy

Scroll for more

Select an answer set to view for
Effect of Temperature on Reaction Rates & the Concept of Activation Energy

Easy
Medium
Hard
1
1 mark

Which factor affects the activation energy of a reaction?

  • the addition of a catalyst

  • a change in the concentration of the reactants

  • a change in pressure

  • a change in temperature

Choose your answer

2
1 mark

The Maxwell-Boltzmann energy distribution curve below describes a mixture of two gases at a given temperature.

Maxwell-Boltzmann energy distribution curve for a mixture of two gases with two activation energy values, Ea1 and Ea2, marked on the x-axis

Of the two activation energy (Ea) values shown, one is for a catalysed reaction, the other for an uncatalysed one.

Which row gives the catalysed and uncatalysed reactions and their relative numbers of effective collisions?

Ea1

Ea2

reaction

effective collisions

reaction

effective collisions

A

uncatalysed

fewer

catalysed

more

B

catalysed

fewer

uncatalysed

more

C

uncatalysed

more

catalysed

fewer

D

catalysed

more

uncatalysed

fewer

    Choose your answer

    3
    1 mark

    The diagram represents the reaction pathway for the following reaction:

    Z (g) + Y (g) → X (g) + W (g)

    Energy profile diagram for the reaction Z (g) + Y (g) → X (g) + W (g), showing reactants at higher energy than products with a transition state peak, indicating an exothermic forward reaction

    Which row gives the properties of the reverse reaction, W (g) + X (g) → Y (g) + Z (g)?

    Activation energy

    ΔH

    A

    smaller

    negative

    B

    smaller

    positive

    C

    larger

    negative

    D

    larger

    positive

      Choose your answer

      1
      1 mark

      The distribution of molecular energies in a sample of a gas at a given temperature is shown by the Boltzmann distribution graph.

      Boltzmann distribution curve for a gas at a given temperature, with point X marked at the peak representing the most probable energy

      The temperature is increased. Which statement describes the new position of X?

      • Fewer molecules possess the most probable energy value so X will shift to the right.

      • Fewer molecules possess the most probable energy value so X will shift to the left.

      • More molecules possess the most probable energy value so X will shift to the left.

      • More molecules possess the most probable energy value so X will shift to the right.

      Choose your answer

      2
      1 mark

      The diagram shows a reaction pathway for an endothermic reaction.

      Which arrow represents the activation energy for the forward reaction?

      Endothermic reaction pathway diagram showing energy against reaction progress, with four arrows A, B, C and D indicating different energy spans between reactants, products and transition state

        Choose your answer

        3
        1 mark

        The dotted-line curve on each graph below represents the corresponding distribution for a gas at 300 K.

        Which solid-line curve represents the distribution of molecular energies in the same mass of gas at 500 K?

        • Boltzmann distribution curves at 300 K (dotted) and 500 K (solid) where the solid curve is shifted to the left of the 300 K curve
        • Boltzmann distribution curves at 300 K (dotted) and 500 K (solid) where the solid curve has a higher, narrower peak at the same position as the 300 K curve
        • Boltzmann distribution curves at 300 K (dotted) and 500 K (solid) where the solid curve is shifted to the right with a higher peak than the 300 K curve
        • Boltzmann distribution curves at 300 K (dotted) and 500 K (solid) where the solid curve is shifted to the right with a lower, broader peak than the 300 K curve

        Choose your answer

        4
        1 mark

        The energies of the reactants, the products and the transition state of a reaction are shown in the reaction pathway diagram.

        Reaction pathway energy diagram showing three energy levels E1, E2 and E3 labelled on the y-axis, with the curve rising from the reactants through a transition state peak and falling to the products

        Which expression represents the activation energy of the forward reaction?

        • E1 - E2

        • E2 - E1

        • E2 - E3

        • E3 - E2

        Choose your answer

        5
        1 mark

        The diagram represents, for a given temperature, the Boltzmann distribution of the kinetic energy of the molecules in a mixture of two gases that react slowly together without a catalyst.

        The activation energy for the reaction, Ea, is marked for the uncatalysed reaction.

        Boltzmann distribution of molecular energies for a reacting gas mixture, with the uncatalysed activation energy Ea marked as a vertical line, and positions A, B, C and D labelled on the energy axis relative to Ea

        Which position represents the activation energy for the catalysed reaction?

          Choose your answer

          6
          1 mark

          Four gas-phase reactions with the same general equation are measured at the same temperature:

          X (g) + Y (g) ⇌ Z (g)

          Which reaction pathway diagram shows the reaction that would proceed most rapidly and with the highest equilibrium yield?

          • Reaction pathway energy profile showing an exothermic reaction with a high activation energy barrier
          • Reaction pathway energy profile showing an exothermic reaction with the lowest activation energy barrier
          • Reaction pathway energy profile showing an endothermic reaction with products at higher energy than reactants
          • Reaction pathway energy profile showing an endothermic reaction with a high activation energy barrier and products above reactants

          Choose your answer

          7
          1 mark

          The diagram shows a Boltzmann distribution of molecular energies for a gaseous mixture. The distribution has a peak, labelled Q on the diagram.

          Boltzmann distribution of molecular energies for a gaseous mixture with the peak labelled Q and the activation energy Ea marked as a vertical line on the energy axis

          Which row gives the changes when a catalyst is added to the mixture?

          Height of peak at Q

          Position of Ea

          A

          remains the same

          moves to the left

          B

          decreases

          moves to the left

          C

          remains the same

          moves to the right

          D

          decreases

          moves to the right

            Choose your answer

            8
            1 mark

            A graph shows the Boltzmann distribution of molecular energies at temperature T1 for a sample of gas. A vertical line represents the activation energy, Ea. A second curve is added for the same sample at a higher temperature, T2.

            Graph showing distribution of molecular energy. Two curves marked T1 and T2 with a vertical line at Ea. X-axis: molecular energy E, Y-axis: proportion of molecules.

            Which statement describes the T2 curve compared to T1?

            • The area under the curve increases and the peak shifts to the right.

            • The activation energy decreases and the peak shifts to the right.

            • The peak shifts to the right and becomes lower.

            • The activation energy decreases and the area under the curve increases.

            Choose your answer

            1
            1 mark

            The following diagrams show Boltzmann distributions.

            Two Boltzmann distribution diagrams. Diagram 1 shows a distribution curve with two vertical lines labelled P and Q at different positions on the energy axis. Diagram 2 shows two distribution curves labelled X and Y with different widths and peak heights.

            In diagram 1, one line, P or Q, corresponds to the activation energy in the presence of a catalyst and the other line corresponds to the activation energy of the same reaction in the absence of a catalyst.

            In diagram 2, one curve, X or Y, corresponds to a higher temperature of the same sample of gas.

            Which row identifies the presence of a catalyst and the higher temperature?

            Presence of catalyst

            Higher temperature

            A

            P

            X

            B

            P

            Y

            C

            Q

            X

            D

            Q

            Y

              Choose your answer

              2
              1 mark

              1 dm3 of gas X and 1 dm3 of gas Y are kept at the same temperature and pressure.

              The speed of the molecules is plotted against the fraction of molecules with that speed.

              Speed distribution curves for gases X and Y at the same temperature and pressure, showing the fraction of molecules at each molecular speed

              Which statement is correct?

              • The molar mass of X is larger than the molar mass of Y

              • The molar mass of Y is larger than the molar mass of X

              • The average kinetic energy of X is higher than that of Y

              • The average kinetic energy of Y is higher than that of X

              Choose your answer

              3
              1 mark

              The diagram shows a Boltzmann distribution of molecular energies with three regions, H, J and K, labelled.

              Boltzmann distribution curve with three regions H, J and K labelled on different parts of the curve

              The temperature is decreased. Which row describes what happens to the size of the areas labelled H, J and K?

              H

              J

              K

              A

              Decreases

              Decreases

              Increases

              B

              Decreases

              Increases

              Decreases

              C

              Increases

              Decreases

              Decreases

              D

              Increases

              Decreases

              Increases

                Choose your answer