# Explain why the law of conservation of mass means that the total mass of products formed in a chemical reaction is always equal to the total mass of the reactants used.

> Eduqas GCSE Chemistry — C3 Quantitative chemistry · Explain · 4 marks

> A student burns a piece of magnesium ribbon in air and notices that the white powder produced appears to have a greater mass than the original magnesium ribbon.

## Mark scheme (4 marks)

1. Atoms are neither created nor destroyed during a chemical reaction
2. Atoms are rearranged / bonds are broken and new bonds are formed
3. The magnesium has reacted with oxygen (from the air) and gained mass because oxygen atoms have been added to the product
4. If the oxygen taken from the air is included, the total mass of reactants (magnesium + oxygen) equals the total mass of products (magnesium oxide)

## Key terms

- [law of conservation of mass](https://www.gradenine.co.uk/glossary/law-of-conservation-of-mass)
- [reactants](https://www.gradenine.co.uk/glossary/reactants)
- [products](https://www.gradenine.co.uk/glossary/products)

## Related

- [Revision notes for Eduqas GCSE Chemistry](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-why-the-law-of-conservation-fdd41d5b) · Published by Druglandscape Ltd.