# A student reacts zinc with excess hydrochloric acid in a sealed container. The equation for the reaction is: Zn + 2HCl → ZnCl₂ + H₂. The student notices that 0.5 mol of hydrogen gas is produced. Avogadro's law states that equal amounts in moles of gases occupy the same volume under the same conditions of temperature and pressure. The molar volume of a gas at room temperature and pressure is 24 dm³/mol. Explain how the student can use Avogadro's law to determine the volume of hydrogen gas produced, and describe what would happen to the volume if the same experiment were repeated at a higher temperature but the same pressure.

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

> Zinc reacts with hydrochloric acid according to the equation: Zn + 2HCl → ZnCl₂ + H₂. In an experiment carried out at room temperature and pressure, 0.5 mol of hydrogen gas is produced. The molar volume of any gas at room temperature and pressure is 24 dm³/mol.

## 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, so 1 mol of any gas occupies 24 dm³ at room temperature and pressure.
2. The volume of 0.5 mol of hydrogen gas at room temperature and pressure is 12 dm³ (0.5 × 24 dm³/mol).
3. At a higher temperature (same pressure), the gas particles have more energy and move faster, so they spread further apart / the gas expands.
4. Therefore the volume of hydrogen gas produced would be greater (larger) at the higher temperature.

## Key terms

- [Avogadro's law](https://www.gradenine.co.uk/glossary/avogadro-s-law)
- [molar volume](https://www.gradenine.co.uk/glossary/molar-volume)
- [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)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-student-reacts-zinc-with-excess-374347f8) · Published by Druglandscape Ltd.