A LevelChemistryCambridge (CIE)Exam Questions8. Reaction KineticsHomogeneous & Heterogeneous Catalysts

Homogeneous & Heterogeneous Catalysts (Cambridge (CIE) A Level Chemistry): Exam Questions

Exam code: 9701

48 mins13 questions

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Homogeneous & Heterogeneous Catalysts

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1
1 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?

  • it lowers the activation energy for the reaction

  • it increases the energy of the reacting molecules

  • when it is used, the reaction proceeds by an alternative reaction pathway

  • changing its concentration affects the rate of oxidation

Choose your answer

2
1 mark

Which statement about the addition of a catalyst to a reversible reaction is correct?

  • the average kinetic energy of the reacting particles increases

  • the enthalpy change of the forward reaction decreases

  • the mass of the catalyst decreases by the end of the reaction

  • the rate of the reverse reaction increases

Choose your answer

3
1 mark

Which row describes the effect of adding a catalyst to a reaction?

activation energy of the alternative pathway

rate of reaction

A

higher

decreases

B

higher

increases

C

lower

decreases

D

lower

increases

    Choose your answer

    1
    1 mark

    Which row describes the catalyst used in the Haber process?

    type of catalysis

    identity of catalyst

    A

    heterogeneous

    iron

    B

    heterogeneous

    vanadium(V) oxide

    C

    homogeneous

    iron

    D

    homogeneous

    vanadium(V) oxide

      Choose your answer

      2
      1 mark

      The diagram shows the Maxwell-Boltzmann distribution of molecular energies for a gaseous mixture. The peak is labelled Q, and the activation energy is marked as Ea.

      Maxwell-Boltzmann distribution curve with peak Q marked at the top and activation energy Ea shown as a vertical line on the x-axis to the right of the peak

      Which row describes the changes to the diagram when an effective catalyst is added?

      height of peak Q

      position of Ea

      A

      decreases

      shifts to the left

      B

      decreases

      shifts to the right

      C

      remains the same

      shifts to the left

      D

      remains the same

      shifts to the right

        Choose your answer

        3
        1 mark

        Which row correctly describes the mechanism of a heterogeneous catalyst?

        phase of catalyst relative to reactants

        way in which rate is increased

        A

        same phase

        forms reactive intermediates

        B

        same phase

        provides a surface for reactants to adsorb onto

        C

        different phase

        forms reactive intermediates

        D

        different phase

        provides a surface for reactants to adsorb onto

          Choose your answer

          1
          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 when the light is less bright. The darkness of the colour of the glass is related to the concentration of silver atoms.

          The reactions involved are shown.

          Reaction 1: Ag+ + Cl– ⇌ 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

          Choose your answer

          2
          1 mark

          The stoichiometry of a catalysed reaction is shown.

          R (g) + S (g) ⇌ 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.

          Graph with amount of product T on the y-axis and time on the x-axis. Both curves begin at the origin and are steepest at time zero. Experiment 1 has a shallower initial gradient and reaches a higher plateau. Experiment 2 has a steeper initial gradient and reaches a lower plateau.

          Which changes to the conditions in experiment 1 could produce the results seen in experiment 2?

          catalyst

          initial amount of reactant R

          A

          less effective

          decreased

          B

          less effective

          increased

          C

          more effective

          decreased

          D

          more effective

          increased

            Choose your answer

            3
            1 mark

            Which statement explains the effect of a catalyst using the Boltzmann distribution?

            • it increases the average kinetic energy of the reacting particles

            • it increases the collision frequency between reactant molecules

            • it increases the proportion of molecules with energy greater than or equal to the activation energy

            • it shifts the position of equilibrium of the reaction

            Choose your answer