# A nurse removes a sealed bag of saline solution from a freezer. The bag contains frozen saline at −5 °C. The nurse places the bag in a warm water bath. Explain what happens to the energy supplied to the saline and its temperature during the entire process of warming from −5 °C until it has fully melted.

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

> Saline solution behaves similarly to pure water and has a definite melting point. The warm water bath supplies energy to the bag at a constant rate throughout.

## Mark scheme (4 marks)

1. The temperature of the frozen saline rises as energy is supplied, because the energy increases the kinetic energy of the particles.
2. At the melting point, the temperature remains constant / does not rise even though energy continues to be supplied.
3. During melting, the energy supplied is used to break the intermolecular forces / bonds between particles rather than raising temperature.
4. The energy supplied during the change of state is the latent heat (of fusion) / specific latent heat of fusion.

## 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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