# Iron reacts with sulfur according to the equation: Fe + S → FeS. A student heats 5.6 g of iron with an excess of sulfur. After the reaction is complete, the student finds that the total mass of the reaction vessel and its contents has not changed. Explain why the mass does not change, identify the limiting reactant in this reaction, and explain what the term limiting reactant means.

> WJEC A-Level Chemistry (Wales) — 3.5 Aromatic chemistry (A-Level only) · Explain · 5 marks

> Iron reacts with sulfur according to the equation: Fe + S → FeS. A student heats 5.6 g of iron with an excess of sulfur. After the reaction is complete, the student finds that the total mass of the reaction vessel and its contents has not changed.

## Mark scheme (5 marks)

1. No atoms are lost or made during a chemical reaction
2. So the mass of the products equals the mass of the reactants (law of conservation of mass)
3. Iron (Fe) is the limiting reactant
4. The limiting reactant is the reactant that is completely used up
5. The limiting reactant limits the amount of products formed

## Key terms

- [limiting reactant](https://www.gradenine.co.uk/glossary/limiting-reactant)
- [excess](https://www.gradenine.co.uk/glossary/excess)

## Related

- [Revision notes for WJEC A-Level Chemistry (Wales)](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/iron-reacts-with-sulfur-according-to-77da9f5b) · Published by Druglandscape Ltd.