# A student uses a reaction profile to compare two reactions: an uncatalysed decomposition of hydrogen peroxide and the same reaction using manganese(IV) oxide as a catalyst. Explain how the reaction profile would differ between the two reactions, and use your answer to explain why the catalysed reaction is faster.

> OCR A-Level Chemistry B: Salters (H433) — 5.2 Energy · Explain · 5 marks

> Hydrogen peroxide decomposes to form water and oxygen. This reaction can be carried out with or without a catalyst. A reaction profile shows the relative energies of reactants and products, the activation energy and the overall energy change of a reaction.

## Mark scheme (5 marks)

1. The activation energy is lower in the catalysed reaction
2. The catalyst provides a different (alternative) reaction pathway
3. The overall energy change (difference in energy between reactants and products) remains the same in both profiles
4. A larger proportion of particles have energy equal to or greater than the (lower) activation energy in the catalysed reaction
5. Therefore there are more successful collisions per unit time, so the rate of reaction increases

## Key terms

- [catalyst](https://www.gradenine.co.uk/glossary/catalyst)
- [reaction profile](https://www.gradenine.co.uk/glossary/reaction-profile)

## Related

- [Revision notes for OCR A-Level Chemistry B: Salters (H433)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-student-uses-a-reaction-profile-1f99baf5) · Published by Druglandscape Ltd.