The molar volume of a gas is simply the volume 1 mole of an ideal gas occupies under certain conditions for pressure and temperature.
For example, the molar volume of a gas at STP represents the volume 1 mole of any ideal gas occupies at a pressure of 100 kPa and a temperature of 273.15 K.
In other words, if those conditions for pressure and temperature are met, 1 mole of any gas will occupy a volume of 22.7 L.
You can determine the molar volume of a gas under any conditions of pressure and temperature by using the ideal gas law equation.
You can rearrange this equation to get
If the pressure is equal to 1 atm and the temperature to 273.15 K, you'll get
If you want to see what volume 1 mole would occupy, simply replace
SIDE NOTE This is the actually the old definition of the molar volume of a gas at STP.
If you have a pressure of 2 atm and a temperature of 355 K, you would get
So, under these specific conditions for pressure and temperature, 1 mole occupies 9.71 L. You would have
- 2 moles
#-># #9.71 * 2 = "19.4 L"#
- 4.5 moles
#-># #9.71 * 4.5 = "43.7 L"#
- 0.05 moles
#-># #9.71 * 0.05 = "0.486 L"#
and so on.
As a conclusion, the molar volume of a gas represents the volume occupied by 1 mole of any ideal gas under specific conditions for temperature and pressure.
If pressure and/or temperature change, the molar volume changes as well.