# Nuclear fusion releases large amounts of energy and is the process that powers stars. Explain why nuclear fusion is difficult to achieve on Earth, and state what happens to the mass of the nuclei during a fusion reaction.

> Pearson Edexcel International GCSE Physics (4PH1) — 7.3 Fission and fusion · Explain · 4 marks

> Scientists have been attempting to harness nuclear fusion as a clean energy source for decades. In fusion, two small, light nuclei are brought together to form a larger, heavier nucleus.

## Mark scheme (4 marks)

1. At low temperatures/pressures the electrostatic repulsion between protons is too great (to allow fusion to occur)
2. Very high temperatures AND very high pressures are required to overcome the electrostatic repulsion
3. These extreme conditions are very difficult to produce and sustain on Earth (making controlled fusion challenging)
4. There is a (very small) loss of mass during fusion, which is converted into energy (mass-energy equivalence)

## Key terms

- [nuclear fusion](https://www.gradenine.co.uk/glossary/nuclear-fusion)

## Related

- [Revision notes for Pearson Edexcel International GCSE Physics (4PH1)](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/nuclear-fusion-releases-large-amounts-of-a5ed7e0d) · Published by Druglandscape Ltd.