# A wood-burning stove is used to heat a room. During this process, 18 000 J of chemical energy is released by burning the wood. Of this, 12 600 J is transferred as useful thermal energy to the room. Describe the useful energy transfer and the waste energy transfer that occur, and explain what is meant by the conservation of energy in this context.

> Pearson Edexcel International GCSE Physics (4PH1) — 4.1 Energy transfers · Describe · 4 marks

> A wood-burning stove releases 18 000 J of chemical energy when wood is burned. Of this, 12 600 J is transferred as useful thermal energy to the room.

## Mark scheme (4 marks)

1. The useful energy transfer is from chemical energy (in the wood) to thermal energy (heating the room).
2. The waste energy transfer is the remaining 5 400 J transferred to the surroundings as thermal energy (e.g. up the chimney / to the outside air) or as light energy from the flames.
3. Conservation of energy means energy cannot be created or destroyed — the total energy before equals the total energy after.
4. The total energy output (useful + waste = 12 600 + 5 400 = 18 000 J) equals the chemical energy input of 18 000 J, demonstrating conservation of energy.

## Key terms

- [chemical energy](https://www.gradenine.co.uk/glossary/chemical-energy)
- [useful energy transfer](https://www.gradenine.co.uk/glossary/useful-energy-transfer)
- [waste energy transfer](https://www.gradenine.co.uk/glossary/waste-energy-transfer)
- [conservation of energy](https://www.gradenine.co.uk/glossary/conservation-of-energy)
- [thermal energy](https://www.gradenine.co.uk/glossary/thermal-energy)

## Related

- [Revision notes for Pearson Edexcel International GCSE Physics (4PH1)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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