# Combustion of fuels is an exothermic process. Explain what the term exothermic means and describe how the energy profile diagram for an exothermic reaction differs from that of an endothermic reaction.

> AQA A-Level Chemistry (7405) — 3.1.4 Energetics · Explain and Describe · 5 marks

> When methane burns in oxygen, energy is released to the surroundings. When citric acid reacts with sodium hydrogencarbonate, the surroundings become colder.

## Mark scheme (5 marks)

1. In an exothermic reaction, energy is transferred TO the surroundings
2. The temperature of the surroundings increases (in an exothermic reaction)
3. On the energy profile diagram for an exothermic reaction, the products are at a lower energy level than the reactants
4. For an endothermic reaction, the products are at a higher energy level than the reactants (on the energy profile diagram)
5. The overall energy change (ΔH) is negative for exothermic and positive for endothermic / the energy difference between reactants and products is greater on the right for endothermic compared to exothermic

## Key terms

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

## Related

- [Revision notes for AQA A-Level Chemistry (7405)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain and Describe" 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/combustion-of-fuels-is-an-exothermic-750c8325) · Published by Druglandscape Ltd.