A LevelChemistryCIEExam Questions1. Physical Chemistry1.8 Reaction Kinetics

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First teaching 2020

Last exams 2024

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Reaction Kinetics (CIE A Level Chemistry)

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1.8 Reaction Kinetics

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1.8 Reaction Kinetics

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11 mark

Which of the following factors can affect the value of the activation energy of a reaction?

1

The presence of a catalyst

2

Changes in temperature

3

Changes in the concentration of the reactants

  • 1 only

  • 1 and 2

  • 3 only

  • 1, 2 and 3

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21 mark

The oxidation of butadiene, CH2=CHCH=CH2, using air or oxygen, produces the molecule crotonaldehyde, CH3CH=CHCHO.

One method of oxidation is to pass a mixture of butadiene and oxygen through a hot aqueous solution of palladium(II) ions, Pd2+ (aq), which catalyse the reaction.

Which statement about the action of the Pd2+ (aq) ions is not correct?

  • Pd2+ (aq) lowers the activation energy for the reaction.

  • Pd2+ (aq) increases the energy of the reacting molecules.

  • When Pd2+ (aq) is used, the reaction proceeds by a different route.

  • Changing the concentration of the Pd2+ (aq) affects the rate of oxidation.

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31 mark

The Maxwell-Boltzmann energy distribution curve below describes a mixture of two gases at a given temperature. For a reaction to occur between the gaseous molecules, they must collide with sufficient energy.

1-8-cie-ial-chemistry-diagram-q3easy

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

When a catalyst is used, which pair of statements is correct?

A

Ea1   uncatalysed reaction

         fewer effective collisions

Ea2   catalysed reaction

         more effective collisions
B

Ea1   catalysed reaction

         fewer effective collisions

Ea2   uncatalysed reaction

         more effective collisions
C

Ea1   uncatalysed reaction

         more effective collisions

Ea2   catalysed reaction

         fewer effective collisions
D

Ea1   catalysed reaction

         more effective collisions

Ea2   uncatalysed reaction

         fewer effective collisions

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    41 mark

    Ammonia is manufactured using the Haber process, which is represented by the following equation:

    N2 (g) + 3H2 (g)  rightwards arrow  2NH3 (g)    ∆H = –93 kJ mol–1

    What happens to the rate of the forward and backward reactions when the temperature is increased?

    • There is no effect on the backward or forward rate.

    • Both forward and backward rates increase.

    • The forward rate only increases.

    • The backward rate only increases.

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    51 mark

    Why does a mixture of hydrogen gas and bromine gas react together faster at a temperature of 500 K than it does at a temperature of 400 K?

    1

    A higher proportion of effective collisions occurs at 500 K.
    2

    Hydrogen molecules and bromine molecules collide more frequently at 500 K.
    3

    The activation energy of the reaction is lower at 500 K.

    • 1 only

    • 1 and 2

    • 3 only

    • 1, 2 and 3

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    61 mark

    When the pressure of a fixed mass of gaseous reactants is raised at a constant temperature, the rate of reaction increases.

    Which of the following statements explain this observation?

    1

    Raising the pressure lowers the activation energy.

    2

    More molecules have energy greater than the activation energy at the higher pressure.

    3

    More collisions occur per second when the pressure is increased.

    • 1 only

    • 1 and 2

    • 3 only

    • 1, 2 and 3

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    71 mark

    What is the main reason for the increase in reaction rate with increasing temperature?

    • The activation energy decreases.

    • The activation energy increases.

    • The molecules collide more frequently.

    • More molecules have an energy greater than the activation energy.

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    81 mark

    The diagram represents the reaction pathway for the following reaction:

    Z (g) + Y (g)  →  X (g) + W (g)

    1-8-cie-ial-chemistry-diagram-q8easy

    What statement is true about the reverse reaction, W (g) + X (g)  →  Y (g) + Z (g)?

    • It will have a smaller activation energy and a negative ∆H

    • It will have a smaller activation energy and a positive ∆H

    • It will have a larger activation energy and a negative ∆H

    • It will have a larger activation energy and a positive ∆H

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    91 mark

    A student measured the rate of a reaction at two different temperatures: 40 °C and 50 °C. They observed that the rate of reaction roughly doubled.

    What explains this observation?

    • Raising the temperature by 10 °C doubles the average velocity of the molecules.

    • Raising the temperature by 10 °C doubles the average kinetic energy of each molecule.

    • Raising the temperature by 10 °C doubles the number of molecules having more than a certain minimum energy.

    • Raising the temperature by 10 °C doubles the number of molecular collisions in a given time.

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    101 mark

    Which statements correctly describe how a catalyst works?

    1

    A catalyst has no effect on the enthalpy change of the reaction.

    2

    A catalyst increases the rate of the reverse reaction.

    3

    A catalyst increases the average kinetic energy of the reacting particles.

    • 1 only

    • 1 and 2

    • 3 only

    • 1, 2 and 3

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    11 mark

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

    1-8-cie-ial-chemistry-diagram-q1medium

    If the temperature is increased, what will happen to the position of point 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.

    • The position of X will stay the same but the area under the distribution curve increases.

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    21 mark

    The diagram shows a reaction pathway for an endothermic reaction.

    Which arrow represents the activation energy for the forward reaction?

    1-8-cie-ial-chemistry-diagram-q2medium

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      31 mark

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

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

      • 1-8-m-3a

      • 1-8-m-3b

      • 1-8-m-3c

      • 1-8-m-3d

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      41 mark

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

      1-8-cie-ial-chemistry-diagram-q4medium

      Which expression correctly represents how to calculate the activation energy of the forward reaction?

      • E1 - E2

      • E2 - E1

      • E2 - E3

      • E3 - E2

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      51 mark

      The diagram below 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.

      What would the position of Ea be if the reaction took place with an effective catalyst?

      1-8-cie-ial-chemistry-diagram-q5medium

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        61 mark

        Four possible reactions (A, B, C and D) of the equation below 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 good yield?

        • 1-8-m-6a

        • 1-8-m-6b

        • 1-8-m-6c

        • 1-8-m-6d

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        71 mark

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

        1-8-cie-ial-chemistry-diagram-q7medium

        What happens when an effective catalyst is added to the mixture?

        • The height of the peak remains the same, and the activation energy moves to the left.

        • The height of the peak decreases and the activation energy moves to the left.

        • The height of the peak remains the same, and the activation energy moves to the right.

        • The height of the peak decreases and the activation energy moves to the right.

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        81 mark

        A student performs two reactions and measures the rate of product formation. 

        Reaction 1: 1.5 g of solid calcium carbonate is added to 100 cm3 of 0.5 M hydrochloric acid.

        Reaction 2: 100 cm3 of distilled water is then added to 100 cm3 of 0.5 M hydrochloric acid then 1.5 g of solid calcium carbonate is added.

        The rate of reaction 1 was faster than the rate of reaction 2. 

        Which of the following 3 hypotheses correctly describes the difference in the rate? 

        1

        Adding water reduces the frequency of collisions between reactant molecules.

        2

        Adding water reduces the proportion of effective collisions between reactant molecules.

        3

        Adding water reduces the proportion of reactant molecules possessing the activation energy.

        • 1 only

        • 1 and 2

        • 3 only

        • 1, 2 and 3

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        91 mark

        The Boltzmann distribution shows the number of molecules that have particular kinetic energy at a constant temperature.

        1-8-cie-ial-chemistry-diagram-q9medium

        If the temperature is decreased by 10 °C, what happens to the size of the areas labelled H, J and K?

         

        H

        J

        K

        A

        B

        C

        D

        Decreases

        Decreases

        Increases

        Increases

        Decreases

        Increases

        Decreases

        Decreases

        Decreases

        Decreases

        Decreases

        Increases

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          1
          Sme Calculator          1 mark

          Photochromic glass is used for some glasses to enable them to work as sunglasses. The glass darkens when exposed to bright light and returns to transparent again when the light is less bright. The darkness of the colour of the glass is related to the concentration of silver atoms. 

          The following reactions are involved.

          Reaction 1

          Ag+ + Cl– rightwards harpoon over leftwards harpoon for blank of Ag + Cl 

          Reaction 2

          Cu+ + Cl → Cu2+ + Cl–

          Reaction 3

          Cu2+ + Ag → Cu+ + Ag+

          Which statement about these reactions is correct?

          • Ag+ ions are oxidised in reaction 1.

          • Cu+ and Cu2+ ions act as catalysts.

          • Cu+ ions act as an oxidising agent in reaction 2.

          • Reaction 2 is the one in which light is absorbed.

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          21 mark

          When 1 cm3 of 0.1 mol dm–3 HCl is added to 10 cm3 of 0.02 mol dm–3 Na2S2O3 pale yellow precipitate forms slowly.

          When the experiment is repeated with 1 cm3 of 0.1 mol dm–3 HCl and 10 cm3 of 0.05 mol dm–3 Na2S2O3 the precipitate forms more quickly.

          Why is this?

          • When 0.05 mol dm–3 Na2S2O3 is used the reactant particles collide more frequently.

          • When 0.05 mol dm–3 Na2S2O3 is used the collisions between reactant particles are more violent.

          • When 0.05 mol dm–3 Na2S2O3 is used the activation energy of the reaction is lower.

          • When 0.05 mol dm–3 Na2S2O3 is used the reaction proceeds by a different pathway.

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          31 mark

          A reaction is zero order with respect to a reactant A.

          Which concentration–time graph for reactant A is the correct shape?

          • 1-8-h-3a

          • 1-8-h-3b

          • 1-8-h-3c

          • 1-8-h-3d

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          41 mark

          A quantity of solid Y was placed in a previously evacuated vessel, and the apparatus was then held at a series of different temperatures. At each temperature, the mass of Y in the vapour state was calculated from pressure measurements. The results are shown below.

          1-8-cie-ial-chemistry-diagram-q4hard

          What can be deduced from the diagram?

          1

          The mass of Y used in the experiment was m.
          2

          The pressure of the vapour was constant for all temperatures above temperature T.
          3

          Liquid appeared at temperature T.

          • 1 only

          • 1 and 3

          • 2 and 3

          • 1, 2 and 3

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          51 mark

          On the graph, curve 1 was produced from measuring the decomposition of 100 cm3 of 1.0 mol dm–3 hydrogen peroxide in the presence of a manganese (IV) oxide catalyst.

          1-8-cie-ial-chemistry-diagram-q5hard

          Which alteration to the original experimental conditions would produce curve 2?

          • Raising the temperature.

          • Adding more manganese (IV) oxide.

          • Adding water.

          •  Adding some 0.1 mol dm–3 hydrogen peroxide.

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          61 mark

          The following exothermic reaction occurs during a fireworks display.

          16Al + 3Ba(NO3)2 + 36H2O → 3Ba(OH)2 + 16Al (OH)3 + 6NH3

          The production of sparkler fireworks requires a mixture of barium nitrate powder and aluminium powder to be mixed with water before being glued on to wires. The wire coating must be dry before lighting the fireworks.

          Which conditions would be best to reduce the rate of this reaction during the drying process, and would also keep the aluminium and barium nitrate unchanged?

           

          pH

          Temperature / K

          A

          B

          C

          D

          7

          14

          7

          14

          298

          298

          398

          398

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            71 mark

            The stoichiometry of a catalysed reaction is shown by the equation below.

            R (g) + S (g)   rightwards harpoon over leftwards harpoon for blank of  T (g) + U (g)

            Two experiments were carried out in which the amount of product T was measured against time. The results are shown in the diagram below.

            1-8-cie-ial-chemistry-diagram-q7hard
            Which changes in the conditions from experiment 1 to experiment 2 might explain the results shown?

            1

            Product U was continuously removed from the equilibrium mixture

            2

            A different catalyst was used

            3

            Less of reactant R was used 

            • 1 only

            • 1 and 3

            • 2 and 3

            • 1, 2 and 3

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            81 mark

            Boltzmann distributions are shown in the diagrams.

            1-8-cie-ial-chemistry-diagram-q8hardIn 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 temperature higher than that of the other curve. 

            Which combination gives the correct curve and line?

             

            Presence of catalyst

            Higher temperature

            A

            B

            C

            D

            P

            P

            Q

            Q

            X

            Y

            X

            Y

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