Since gases expand and contract depending on the pressure and temperature, we use STP (Standard Temperature and Pressure to make sure all gases are measured accurately. 1 mole of gas is to take up 22 L, at 1 atmostphere of pressure and a temerature of 0°.
Converting from molà litres
Ex: Calculate the volume (L) of 20mole of ammonia at STP
20mol x 22.4L = 448L
Converting from litresà mol
Ex: Calculate the number of moles in 5.54 L of CO2 at STP
5.54L x 1 mole = 0.247 mol