# A sealed balloon is filled with a fixed quantity of gas at room temperature. The balloon is then placed in a freezer. Explain, using kinetic theory, why the volume of the balloon decreases when it is placed in the freezer.

> WJEC GCSE Physics (Wales) — 2.2 The kinetic theory and gas pressure · Explain · 4 marks

## Mark scheme (4 marks)

1. Lowering the temperature decreases the average kinetic energy of the gas molecules
2. The molecules move more slowly / with lower speeds
3. The molecules collide with the walls of the balloon less frequently and/or with less force
4. The pressure exerted by the gas on the balloon walls decreases, so the balloon shrinks until the internal pressure equals the external (atmospheric) pressure

## Key terms

- [kinetic theory](https://www.gradenine.co.uk/glossary/kinetic-theory)
- [temperature](https://www.gradenine.co.uk/glossary/temperature)
- [volume](https://www.gradenine.co.uk/glossary/volume)

## Related

- [Revision notes for WJEC GCSE Physics (Wales)](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-sealed-balloon-is-filled-with-a4bd5f74) · Published by Druglandscape Ltd.