# When water is heated from room temperature until it boils, its particles gain energy and the state changes from liquid to gas. Explain, in terms of particles and intermolecular forces, why water has a fixed volume as a liquid but no fixed volume as a gas.

> Pearson Edexcel International GCSE Chemistry (4CH1) — 1.1 States of matter · Explain · 4 marks

> Water exists as a liquid at room temperature and pressure. When heated to 100 °C it becomes a gas (steam).

## Mark scheme (4 marks)

1. In a liquid, particles are close together / touching / in contact with each other
2. In a liquid, intermolecular forces hold the particles together / keep them within a fixed space, giving a fixed volume
3. In a gas, particles have much more energy and move rapidly in all directions / are widely/randomly spread out
4. In a gas, intermolecular forces are (effectively) overcome / negligible / absent, so particles are not held together and expand to fill any container, giving no fixed volume

## Key terms

- [intermolecular forces](https://www.gradenine.co.uk/glossary/intermolecular-forces)
- [liquid](https://www.gradenine.co.uk/glossary/liquid)
- [gas](https://www.gradenine.co.uk/glossary/gas)
- [particles](https://www.gradenine.co.uk/glossary/particles)
- [fixed volume](https://www.gradenine.co.uk/glossary/fixed-volume)

## Related

- [Revision notes for Pearson Edexcel International GCSE Chemistry (4CH1)](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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