# A student says: 'Nuclear fusion releases energy because the total mass of the products is less than the total mass of the reactants.' Explain why the products having less mass means that energy is released, and describe the conditions needed for nuclear fusion to occur.

> Eduqas A-Level Physics — 3.6 Nuclear energy · Explain · 5 marks

## Mark scheme (5 marks)

1. The missing mass has been converted into energy (mass-energy equivalence / Einstein's equation E = mc²)
2. Because c (the speed of light) is very large, even a tiny mass produces a very large amount of energy
3. Nuclear fusion requires extremely high temperatures (accept: millions of degrees / temperatures comparable to the core of the Sun)
4. The nuclei must be moving fast enough (have enough kinetic energy) to overcome the electrostatic repulsion between them / get close enough to fuse
5. Very high pressure / density is also needed to increase the chance of nuclei colliding (accept: to confine the plasma / to increase collision frequency)

## Key terms

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

## Related

- [Revision notes for Eduqas A-Level Physics](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-says-nuclear-fusion-releases-dfadc4e7) · Published by Druglandscape Ltd.