# Avogadro's law states that equal amounts in moles of gases occupy the same volume under the same conditions of temperature and pressure. Explain how a chemist can use Avogadro's law and a balanced chemical equation to predict the volume of gas produced in a reaction, without needing to know the mass of the gas.

> AQA GCSE Chemistry (8462) — 4.3.5 Use of amount of substance in relation to volumes of gases (Chem only) · Explain · 4 marks

> At room temperature and pressure, one mole of any gas occupies a volume of 24 dm³. A student reacts excess zinc with dilute hydrochloric acid and wants to predict the volume of hydrogen gas produced from 0.25 mol of hydrochloric acid. The equation for the reaction is: Zn + 2HCl → ZnCl₂ + H₂

## Mark scheme (4 marks)

1. Avogadro's law means equal moles of any gas occupy the same volume (at the same temperature and pressure)
2. The balanced equation shows the mole ratio of reactants to gaseous product (2 mol HCl produces 1 mol H₂, so 0.25 mol HCl produces 0.125 mol H₂)
3. The molar volume (24 dm³ per mole at room temperature and pressure) is multiplied by the number of moles of gas to give the volume
4. The predicted volume of hydrogen produced is 3 dm³ (0.125 × 24 = 3 dm³)

## Key terms

- [Avogadro's law](https://www.gradenine.co.uk/glossary/avogadro-s-law)
- [mole](https://www.gradenine.co.uk/glossary/mole)

## 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/avogadro-s-law-states-that-equal-amounts-3588a9ac) · Published by Druglandscape Ltd.