GCSE Chemistry: Use of amount of substance in relation to volumes of gases

All questions and answers

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1. What is the volume of one mole of any gas at room temperature and pressure?

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   24 dm³.

2. What temperature and pressure define room temperature and pressure (RTP) in GCSE chemistry?

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   20 °C and 1 atmosphere pressure.

3. Equal amounts in moles of gases occupy the ? volume under the same conditions of temperature and pressure.

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   same

4. Under what two conditions do equal moles of different gases occupy equal volumes?

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   The same temperature and the same pressure.

5. How do you calculate the volume of a gas at RTP from its mass?

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   Divide mass by relative formula mass to get moles, then multiply moles by 24 dm³.

6. What volume does 0.5 mol of any gas occupy at RTP?

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   12 dm³ (0.5 × 24 dm³).

7. What volume does 4 g of hydrogen gas (H₂, Mr = 2) occupy at RTP?

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   48 dm³ (4 ÷ 2 = 2 mol; 2 × 24 dm³).

8. What information is needed to calculate the volumes of gaseous reactants and products in a reaction?

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   The balanced equation for the reaction (plus one known gas volume, all at the same temperature and pressure).

9. In 2H₂ + O₂ → 2H₂O, what volume of oxygen reacts with 40 dm³ of hydrogen at RTP?

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   20 dm³ — the equation gives a 2:1 mole ratio, and equal moles of gas occupy equal volumes.

10. Rearrange volume = moles × 24 to make moles the subject.

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    moles = volume ÷ 24 (volume in dm³ at RTP).