# Combustion is an exothermic reaction. Explain, in terms of bond breaking and bond forming, why the temperature of the surroundings increases when a fuel burns completely in oxygen.

> Edexcel GCSE Chemistry (1CH0) — 7.2 Heat energy changes in chemical reactions · Explain · 4 marks

## Mark scheme (4 marks)

1. Bond breaking occurs in the reactants (fuel and oxygen)
2. Bond breaking requires/takes in energy
3. Bond forming occurs in the products and releases energy
4. The energy released from forming bonds in the products is greater than the energy needed to break bonds in the reactants, so energy is transferred to the surroundings

## Key terms

- [exothermic reaction](https://www.gradenine.co.uk/glossary/exothermic-reaction)
- [bond breaking](https://www.gradenine.co.uk/glossary/bond-breaking)
- [bond forming](https://www.gradenine.co.uk/glossary/bond-forming)
- [surroundings](https://www.gradenine.co.uk/glossary/surroundings)

## Related

- [Revision notes for Edexcel GCSE Chemistry (1CH0)](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/combustion-is-an-exothermic-reaction-explain-0494b7b4) · Published by Druglandscape Ltd.