Volumes of Gases

This lesson covers how to calculate the volume of a gas at room temperature and pressure (RTP), and how to use gas volumes in calculations involving balanced equations. This is required by the Edexcel GCSE Chemistry specification (1CH0) and is a Higher tier topic.

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Molar Gas Volume

At room temperature and pressure (RTP) — defined as 20°C (293 K) and 1 atmosphere (101.3 kPa) — one mole of any gas occupies a volume of 24 dm³ (or 24,000 cm³).

This value is called the molar gas volume.

Condition	Temperature	Pressure	Molar volume
RTP	20°C	1 atm	24 dm³/mol

This means:

• 1 mol of hydrogen gas (H₂) occupies 24 dm³ at RTP
• 1 mol of oxygen gas (O₂) occupies 24 dm³ at RTP
• 1 mol of carbon dioxide (CO₂) occupies 24 dm³ at RTP
• 1 mol of any gas occupies 24 dm³ at RTP