# Explain why two different ideal gases, when mixed together in a sealed container at constant temperature, exert a greater total pressure than either gas alone occupying the same container.

> IB DP Chemistry Standard Level (2023 syllabus) — S1.5 Ideal gases · Explain · 4 marks

> A sealed rigid container holds a mixture of two ideal gases, nitrogen and argon, at room temperature.

## Mark scheme (4 marks)

1. Each gas exerts its own partial pressure independently of the other gas (Dalton's law of partial pressures).
2. Total pressure equals the sum of the individual partial pressures of all gases present.
3. In an ideal gas, molecules have negligible volume and no intermolecular forces, so adding more molecules to the same volume increases the frequency of collisions with the container walls.
4. Because the gases are ideal, there are no intermolecular forces between particles of different gases, so each gas behaves independently and its contribution to pressure is unaffected by the presence of the other gas.

## Key terms

- [ideal gas](https://www.gradenine.co.uk/glossary/ideal-gas)

## Related

- [Revision notes for IB DP Chemistry Standard Level (2023 syllabus)](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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