# A sealed, rigid container holds a fixed quantity of gas. The container is placed in a freezer and the temperature of the gas decreases. Explain, in terms of particles, why the pressure of the gas decreases as its temperature falls.

> WJEC A-Level Physics (Wales) — 2.3 Capacitance (A-Level only) · Explain · 5 marks

## Mark scheme (5 marks)

1. Temperature is a measure of the average kinetic energy of the particles
2. As temperature decreases, the average kinetic energy (and speed) of the particles decreases
3. Slower particles collide with the container walls with less force
4. The particles also collide with the walls less frequently
5. Pressure is the perpendicular force per unit area on the container walls, so with less force and fewer collisions, the pressure decreases

## Key terms

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

## 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-rigid-container-holds-a-f194a63d) · Published by Druglandscape Ltd.