# A student is investigating two reactions, Reaction X and Reaction Y, both producing the same product. Reaction X is exothermic with a high activation energy. Reaction Y is also exothermic but has a much lower activation energy. The student adds a catalyst to Reaction X. Explain how the catalyst increases the rate of Reaction X, and explain how the reaction profile of Reaction X would change after the catalyst is added.

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

> Reaction X: exothermic, high activation energy, slow rate at room temperature. Reaction Y: exothermic, low activation energy, fast rate at room temperature.

## Mark scheme (5 marks)

1. The catalyst provides a different reaction pathway
2. The catalyst lowers the activation energy
3. A greater proportion of particles now have energy at least equal to the (lower) activation energy
4. The catalyst is not used up during the reaction
5. On the reaction profile, the peak (activation energy barrier) would be lower, but the overall energy change (difference in energy between reactants and products) would remain the same

## Key terms

- [activation energy](https://www.gradenine.co.uk/glossary/activation-energy)
- [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-is-investigating-two-reactions-850003b2) · Published by Druglandscape Ltd.