# A student uses a reaction profile to compare two reactions. Reaction X has a small difference in energy between the reactants and the transition state, while Reaction Y has a large difference in energy between the reactants and the transition state. Both reactions release energy overall. Explain what the reaction profile tells us about the activation energy of each reaction and how this affects the rate at which each reaction proceeds at the same temperature.

> OCR A-Level Chemistry A (H432) — 5.2 Energy · Explain · 5 marks

> Reaction profiles show the relative energies of reactants and products, the activation energy, and the overall energy change of a reaction. Reaction X and Reaction Y are both exothermic and are carried out at the same temperature.

## Mark scheme (5 marks)

1. The activation energy is the minimum amount of energy that particles must collide with in order to react
2. Reaction X has a lower activation energy than Reaction Y because the energy difference between the reactants and the transition state is smaller
3. At the same temperature, a larger proportion of particles in Reaction X will have energy equal to or greater than the activation energy
4. Therefore Reaction X has a faster rate of reaction than Reaction Y
5. Both reactions are exothermic, so on a reaction profile the energy of the products is lower than the energy of the reactants for both X and Y

## Key terms

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

## Related

- [Revision notes for OCR A-Level Chemistry A (H432)](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-65b61c53) · Published by Druglandscape Ltd.