# Explain, using the kinetic model of an ideal gas, why a fixed mass of ideal gas occupies a greater volume at constant pressure when its temperature is increased.

> IB DP Physics Higher Level (2023 syllabus) — B.3 Gas laws · Explain · 4 marks

## Mark scheme (4 marks)

1. Increasing temperature means the molecules have greater average kinetic energy / move faster on average.
2. Faster-moving molecules strike the walls with greater force / impulse, so the pressure would tend to increase if the volume were unchanged.
3. At constant pressure the volume must increase so that the force per unit area on the walls remains unchanged / to restore pressure to its original value.
4. As volume increases, molecules travel farther between collisions / average separation increases, so collisions with the walls become less frequent, reducing pressure back to its original value.

## Key terms

- [kinetic model](https://www.gradenine.co.uk/glossary/kinetic-model)
- [ideal gas](https://www.gradenine.co.uk/glossary/ideal-gas)
- [pressure](https://www.gradenine.co.uk/glossary/pressure)

## Related

- [Revision notes for IB DP Physics Higher Level (2023 syllabus)](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/explain-using-the-kinetic-model-of-33e437c4) · Published by Druglandscape Ltd.