Molar volume of gases

One mole of any gas has a volume of 24 dm3 or 24,000 cm3 at rtp (room temperature and pressure). This volume is called the molar volume of a gas.

This equation shows how the volume of gas in dm3 at rtp is related to the number of moles:

volume of gas at rtp = number of moles × 24

Calculate the volume of 0.5 mol of carbon dioxide at rtp.

volume = 0.5 × 24 = 12 dm3

Remember that 1 dm3 = 1 000 cm3 so the volume is also 12 000 cm3

The equation can be rearranged to find the number of moles, if the volume of gas at rtp is known:

number of moles = volume of gas at rtp ÷ 24


Calculate the number of moles of hydrogen that occupy 6 dm3 at rtp.

number of moles = 6 ÷ 24 = 0.25 mol

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