# Magnesium reacts with hydrochloric acid according to the equation: Mg + 2HCl → MgCl₂ + H₂. A student adds an excess of hydrochloric acid to a small amount of magnesium. Explain what is meant by the term 'limiting reactant' and explain why the magnesium is the limiting reactant in this reaction.

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

## Mark scheme (5 marks)

1. The limiting reactant is the reactant that is completely used up during the reaction
2. The limiting reactant limits / controls the amount of products formed
3. The hydrochloric acid is in excess, meaning there is more than enough acid to react with all of the magnesium
4. The magnesium is completely used up / runs out before the hydrochloric acid
5. Once the magnesium is used up, no more hydrogen / magnesium chloride can be produced, so magnesium limits the amount of product

## 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)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/magnesium-reacts-with-hydrochloric-acid-according-37e2be14) · Published by Druglandscape Ltd.