# A fixed quantity of gas is sealed inside a container at a constant temperature. The volume of the container is gradually reduced. Explain, in terms of particles, why the pressure of the gas increases as the volume decreases.

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

## Mark scheme (5 marks)

1. The gas particles collide with the walls of the container, producing pressure.
2. When the volume decreases, the particles are closer together / the space between particles is reduced.
3. The particles collide with the walls more frequently / there are more collisions per second with the walls.
4. Temperature is constant, so the average kinetic energy / speed of the particles remains the same.
5. Greater frequency of collisions means a greater (perpendicular) force per unit area on the walls, so pressure increases.

## Key terms

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

## Related

- [Revision notes for Eduqas A-Level Physics](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-fixed-quantity-of-gas-is-58cc24b0) · Published by Druglandscape Ltd.