# Solid carbon dioxide (dry ice) turns directly into a gas at −78 °C without first becoming a liquid. This process is called sublimation. Explain, in terms of particles, why energy must be supplied for sublimation to occur, and why the resulting gas occupies a much larger volume than the solid.

> Pearson Edexcel International GCSE Chemistry (4CH1) — 1.1 States of matter · Explain · 4 marks

> Solid carbon dioxide (dry ice) sublimes at −78 °C at atmospheric pressure, changing directly from a solid to a gas.

## Mark scheme (4 marks)

1. In the solid, particles are held in fixed positions by strong forces of attraction (between particles).
2. Energy is needed to overcome these forces of attraction between the particles.
3. In the gas, the particles are much more spread out / far apart compared to the solid.
4. In the gas, particles move rapidly and randomly in all directions, so the gas fills the available space / volume.

## Key terms

- [sublimation](https://www.gradenine.co.uk/glossary/sublimation)
- [particles](https://www.gradenine.co.uk/glossary/particles)
- [gas](https://www.gradenine.co.uk/glossary/gas)
- [solid](https://www.gradenine.co.uk/glossary/solid)

## Related

- [Revision notes for Pearson Edexcel International GCSE Chemistry (4CH1)](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/solid-carbon-dioxide-dry-ice-turns-e21bbee9) · Published by Druglandscape Ltd.