# When magnesium burns in oxygen, combustion occurs and a white powder is produced. Explain, in terms of bond breaking and bond forming, why combustion reactions are exothermic.

> AQA GCSE Chemistry (8462) — 4.5.1 Exothermic and endothermic reactions · Explain · 4 marks

## Mark scheme (4 marks)

1. Energy must be supplied to break bonds in the reactants
2. Energy is released when bonds are formed in the products
3. In an exothermic reaction, the energy released from forming bonds is greater than the energy needed to break bonds
4. The overall energy change means energy is transferred to the surroundings, so the temperature of the surroundings increases

## Key terms

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

## Related

- [Revision notes for AQA GCSE Chemistry (8462)](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/when-magnesium-burns-in-oxygen-combustion-cc2f62a8) · Published by Druglandscape Ltd.