A LevelChemistryCIETopic Questions8. Reaction Kinetics8.3 Homogeneous & Heterogeneous Catalysts

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First teaching 2023

First exams 2025

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Homogeneous & Heterogeneous Catalysts (CIE A Level Chemistry)

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11 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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21 mark

Which statements correctly describe how a catalyst works?

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

  • A catalyst increases the rate of the reverse reaction.

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

  • The mass of the reactant changes after the reaction

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31 mark

The addition of a catalyst to a reaction provides an alternate mechanism with

  • Lower activation energy and lower reaction rate

  • Lower activation energy and higher reaction rate

  • Higher activation energy and lower reaction rate

  • Higher activation energy and higher reaction rate

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1
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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

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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31 mark

How does the Boltzmann distribution explain the effect of a catalyst?

  • It shows that a catalyst increases the overall energy of the reactant molecules.

  • It shows that a catalyst increases the number of molecules with energy higher than the activation energy.

  • It shows that a catalyst shifts the equilibrium position of the reaction.

  • It shows that a catalyst increases the rate of collisions between reactant molecules.

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11 mark

Which of the following is involved in the Haber process?

  • a heterogeneous iron catalyst

  • a homogeneous iron catalyst

  • a heterogeneous vanadium catalyst

  • a homogeneous vanadium catalyst

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21 mark

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

2-1

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 right

  • 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 left

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

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31 mark

The addition of a catalyst to a reaction provides an alternate mechanism with

  • lower activation energy and lower reaction rate

  • lower activation energy and higher reaction rate

  • higher activation energy and lower reaction rate

  • higher activation energy and higher reaction rate

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