# A sealed metal can contains a fixed amount of gas. The can is placed in a freezer and the temperature of the gas decreases. Explain, in terms of the movement of gas molecules, why the pressure of the gas inside the can decreases as the temperature falls.

> WJEC A-Level Physics (Wales) — 4.1 Thermal physics · Explain · 5 marks

## Mark scheme (5 marks)

1. Gas molecules are in constant random motion / are moving
2. Pressure is caused by molecules colliding with the walls of the container
3. As temperature decreases, the molecules move more slowly / have less kinetic energy
4. The molecules collide with the walls less frequently / less often
5. Each collision exerts a smaller force on the walls, so overall pressure is lower

## Key terms

- [pressure](https://www.gradenine.co.uk/glossary/pressure)
- [temperature](https://www.gradenine.co.uk/glossary/temperature)
- [molecules](https://www.gradenine.co.uk/glossary/molecules)

## Related

- [Revision notes for WJEC A-Level 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-metal-can-contains-a-85d1ec2e) · Published by Druglandscape Ltd.