# Dry ice is solid carbon dioxide. At room temperature, dry ice undergoes sublimation. Explain what happens to the particles of carbon dioxide during sublimation, and why the mass of carbon dioxide is conserved even though the substance appears to disappear.

> OCR GCSE Physics A: Gateway Science (J249) — P1.2 Changes of state · Explain · 4 marks

> Dry ice is used in theatres to create a low-lying mist effect. Stage crew notice that blocks of dry ice left in a warm room gradually shrink and vanish without leaving any liquid behind.

## Mark scheme (4 marks)

1. Sublimation is the direct change of state from solid to vapour/gas without passing through the liquid phase
2. The particles gain enough energy (latent heat / thermal energy from surroundings) to overcome the intermolecular forces holding them in fixed positions
3. The particles spread apart and move freely with high kinetic energy, forming a gas
4. Mass is conserved because the same number of carbon dioxide particles exists as a gas as existed in the solid; no particles are created or destroyed during a change of state, which is a physical change

## Key terms

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

## Related

- [Revision notes for OCR GCSE Physics A: Gateway Science (J249)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/dry-ice-is-solid-carbon-dioxide-5b3c68b4) · Published by Druglandscape Ltd.