# A student is investigating two different reactions. Reaction A is exothermic and Reaction B is endothermic. Using your knowledge of reaction profiles and activation energy, explain how energy changes during a chemical reaction and how a catalyst affects the rate of reaction.

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

> A student notices that one reaction releases heat to the surroundings whilst another reaction takes in heat from the surroundings. Both reactions can be sped up by adding a suitable catalyst.

## Mark scheme (5 marks)

1. A reaction profile shows the relative energies of reactants and products and the activation energy of the reaction
2. Activation energy is the minimum amount of energy that particles must collide with to react
3. In an exothermic reaction the products have less energy than the reactants, so energy is released to the surroundings
4. In an endothermic reaction the products have more energy than the reactants, so energy is absorbed from the surroundings
5. A catalyst increases the rate of reaction by providing a different reaction pathway with a lower activation energy, and it is not used up during the reaction

## Key terms

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

## 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-is-investigating-two-different-78a77a67) · Published by Druglandscape Ltd.