# Iron reacts with sulfur to form iron sulfide. The equation for this reaction is: Fe + S → FeS. Explain why the mass of iron sulfide produced is greater than the mass of iron used, even though no atoms are lost or made during the reaction. Use the idea of relative formula mass in your answer.

> AQA GCSE Chemistry (8462) — 4.3.2 Use of amount of substance in relation to masses of pure substances · Explain · 4 marks

> A student heats 5.6 g of iron with an excess of sulfur. After the reaction, the student notices that the mass of the solid product is greater than 5.6 g.

## Mark scheme (4 marks)

1. The law of conservation of mass states that no atoms are lost or made during a chemical reaction
2. Both iron and sulfur atoms are incorporated into the product, so the mass of iron sulfide includes the mass of both reactants
3. The relative formula mass of FeS (88) is greater than the relative atomic mass of Fe alone (56)
4. Therefore the product has a greater mass than the iron alone because it also includes the mass of the sulfur that reacted

## Key terms

- [relative formula mass](https://www.gradenine.co.uk/glossary/relative-formula-mass)

## Related

- [Revision notes for AQA GCSE Chemistry (8462)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/iron-reacts-with-sulfur-to-form-0d5819cf) · Published by Druglandscape Ltd.