# Explain, using the particle model, what happens to the particles when a solid substance is heated and melts, and state one limitation of the particle model in describing this process.

> WJEC A-Level Chemistry (Wales) — 2.3 Transition metals (A-Level only) · Explain · 5 marks

> A student heats a solid substance and observes it changing to a liquid at its melting point. The student uses the particle model to explain what they see.

## Mark scheme (5 marks)

1. In a solid, particles are held in fixed positions / arranged in a regular pattern
2. When heated, the particles gain (kinetic/thermal) energy
3. The forces between the particles are overcome / weakened, allowing particles to move more freely
4. This change of state (melting) is a physical change, so the chemical composition of the substance does not change
5. One limitation of the particle model: the model does not show forces between particles / all particles are represented as identical solid spheres / the model does not explain why some substances have higher melting points than others

## Key terms

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

## Related

- [Revision notes for WJEC A-Level Chemistry (Wales)](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-particle-model-what-672039f5) · Published by Druglandscape Ltd.