# A sealed metal cylinder contains a fixed mass of gas. The cylinder is placed in a freezer and left until the gas reaches a much lower temperature. Explain what happens to the pressure of the gas as its temperature decreases, in terms of the molecules of the gas.

> AQA A-Level Physics (7408) — 3.6.2 Thermal Physics · Explain · 5 marks

## Mark scheme (5 marks)

1. The molecules move more slowly / have less kinetic energy at lower temperature
2. The molecules hit the walls of the cylinder less frequently / less often
3. Each collision exerts a smaller force on the wall / molecules hit the walls with less force
4. The volume of the cylinder remains constant (so the same area of wall is being hit)
5. Therefore the pressure of the gas decreases

## Key terms

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

## Related

- [Revision notes for AQA A-Level Physics (7408)](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-cylinder-contains-a-338eb1f1) · Published by Druglandscape Ltd.