Explain how adding a catalyst increases the rate of a chemical reaction.

AQA GCSE Chemistry (8462) — 4.6.1 Rate of reaction · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

A student notices that hydrogen peroxide solution decomposes very slowly at room temperature, but decomposes rapidly when manganese(IV) oxide is added.

Model answer (4 marks)

A catalyst provides an alternative reaction pathway.
The alternative pathway has a lower activation energy.
Because the activation energy is lower, a greater proportion of the reacting particles have sufficient energy to react.
The catalyst is not consumed and is unchanged at the end of the reaction.

Examiner tips

  • Use the phrase "alternative reaction pathway" and "lower activation energy". Show the link between lower activation energy and more particles with enough energy. Remember to state that the catalyst is unchanged.
  • common_mistakes
  • :
  • Confusing a catalyst with a reactant or product. Forgetting to mention that the catalyst is unchanged after the reaction.

Mark scheme (4 marks)

  1. A catalyst provides a different (reaction) pathway
  2. The new pathway has a lower activation energy
  3. A greater proportion of particles have energy equal to or greater than the (lower) activation energy
  4. The catalyst is not used up / is unchanged at the end of the reaction

Key terms in this question

catalyst

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