# Describe how Avogadro's law can be used to compare the volumes of gases produced in different reactions, and explain why this is only valid under the same conditions of temperature and pressure.

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

> Magnesium reacts with dilute sulfuric acid to produce magnesium sulfate and hydrogen gas. Calcium carbonate reacts with dilute hydrochloric acid to produce calcium chloride, water, and carbon dioxide gas. A student wants to compare the volumes of gas produced when equal moles of each acid are used in excess with the respective solid reactants.

## Mark scheme (4 marks)

1. Avogadro's law states that equal amounts in moles of gases occupy the same volume under the same conditions of temperature and pressure
2. The molar ratio from the balanced equation determines the moles of gas produced, so reactions producing more moles of gas per mole of reactant give a greater volume
3. If temperature changes, the volume of a gas changes, so comparisons would not be valid at different temperatures
4. If pressure changes, the volume of a gas changes, so comparisons would not be valid at different pressures

## Key terms

- [Avogadro's law](https://www.gradenine.co.uk/glossary/avogadro-s-law)
- [temperature and pressure](https://www.gradenine.co.uk/glossary/temperature-and-pressure)
- [volume](https://www.gradenine.co.uk/glossary/volume)

## Related

- [Revision notes for AQA GCSE Chemistry (8462)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/describe-how-avogadro-s-law-can-be-584684f6) · Published by Druglandscape Ltd.