# Iron reacts with sulfur to form iron sulfide. A student carries out this reaction and notices that the total mass of the products is equal to the total mass of the reactants. Explain why the mass of the products equals the mass of the reactants in this reaction, and explain what is meant by the term 'limiting reactant' in a chemical reaction where one reactant is used in excess.

> Eduqas A-Level Chemistry — 3.6 Amines and polymers (A-Level only) · Explain · 5 marks

> Iron reacts with sulfur according to the equation: Fe + S → FeS. A student measures the mass of iron and sulfur before the reaction, and the mass of iron sulfide after the reaction, and finds the total mass does not change.

## 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 (conservation of mass)
3. This is described by the law of conservation of mass
4. The limiting reactant is the reactant that is completely used up in the reaction
5. The limiting reactant limits / determines the amount of product formed

## Key terms

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

## Related

- [Revision notes for Eduqas A-Level 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/iron-reacts-with-sulfur-to-form-d02e39bf) · Published by Druglandscape Ltd.