# A student burns a piece of wood in a closed container. The student notices that the total mass of the container and its contents does not change during the reaction. The student then opens the container and finds that the mass of solid remaining is less than the original mass of the wood. Explain why the total mass does not change during burning in the closed container, and why the mass of solid remaining appears less after the container is opened.

> Edexcel GCSE Chemistry (1CH0) — 1.8 Calculations involving masses · Explain · 4 marks

## Mark scheme (4 marks)

1. The law of conservation of mass states that mass is neither created nor destroyed in a chemical reaction
2. In a closed container, no substances can enter or leave, so all products are retained and the total mass remains the same
3. When wood burns it reacts with oxygen to produce gaseous products (such as carbon dioxide and water vapour)
4. When the container is opened, the gaseous products escape into the surroundings, so only the solid ash/residue remains, making the measured solid mass less than the original

## Key terms

- [closed container](https://www.gradenine.co.uk/glossary/closed-container)

## Related

- [Revision notes for Edexcel GCSE Chemistry (1CH0)](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-student-burns-a-piece-of-1eb051ed) · Published by Druglandscape Ltd.