# Explain, using the second law of thermodynamics and the concept of entropy, why a refrigerator requires a continuous external energy input in order to operate.

> IB DP Physics Higher Level (2023 syllabus) — B.4 Thermodynamics (HL only) · Explain · 4 marks

## Mark scheme (4 marks)

1. Heat flows naturally from hot to cold / energy will not spontaneously transfer from a cold reservoir to a hot reservoir
2. A refrigerator transfers thermal energy from a cold interior to a warmer surroundings, which is a non-spontaneous process
3. Such a process would decrease the total entropy of the universe, violating the second law
4. External work input increases the entropy of the surroundings (hot reservoir) by enough to ensure the total entropy of the universe does not decrease / overall entropy change is zero or positive

## Key terms

- [second law of thermodynamics](https://www.gradenine.co.uk/glossary/second-law-of-thermodynamics)
- [entropy](https://www.gradenine.co.uk/glossary/entropy)

## Related

- [Revision notes for IB DP Physics Higher Level (2023 syllabus)](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-second-law-of-4525e2bb) · Published by Druglandscape Ltd.