1.20 understand the term molar volume of a gas and use its values (24 dm3 and 24,000 cm3) at room temperature and pressure in calculations.

The space that one mole of gas takes up is called its molar volume.

At room temperature and pressure, one mole of any gas always occupies 24 dm3 (equivalent to 24,000 cm3) - room temperature is 25 ºc and room pressure is 1 atmosphere (atm).

In calculations, use the equations below to convert the number of moles or mass of any gas to a volume…

Volume (dm3) = moles of gas x 24

Volume (dm3) = (mass of gas / Mr of gas) x 24

For example: Whats the volume of 4.5 moles of chlorine at RTP?

Volume (dm3) = 4.5 x 24 = 108 dm3

Example two: How many moles are there in 8280cm3 of hydrogen gas at RTP?

Volume of gas = moles of gas x 24 therefore, moles of gas = volume of gas / 24

One more thing, we need to convert 8280cm3 into dm3. To do this, just divide by 1000.

8280 / 1000 = 8.28

Now substitute into the rearranged equation…

moles of gas = volume of gas / 24 = 8.28 / 24 = 0.345 moles

NOTE: RTP just means room temperature and pressure