# A chocolate manufacturer heats solid chocolate in a large vat until it melts completely. Once all the chocolate has melted, the manufacturer notices that the mass of the liquid chocolate is the same as the mass of the solid chocolate before heating. Explain why the mass is conserved during this change of state, and describe how the physical properties of the chocolate differ between the solid and liquid states in terms of particles.

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

> A chocolate manufacturer heats solid chocolate in a large vat until it melts completely. The manufacturer records the mass before and after melting and finds it is unchanged.

## Mark scheme (4 marks)

1. Melting is a physical change, not a chemical change, so no particles are created or destroyed.
2. The change of state is reversible and the chocolate retains its original properties when re-solidified.
3. In the solid state, particles are tightly packed together and can only vibrate about their fixed positions, held by strong intermolecular forces.
4. In the liquid state, particles are still in contact but can flow over each other, with intermolecular forces still acting between them.

## Key terms

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

## 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)
- [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-chocolate-manufacturer-heats-solid-chocolate-0fbf367f) · Published by Druglandscape Ltd.