van der Waals' equation for calculating the pressure of a non ideal gas is
van der Waals' suggested that the pressure exerted by an ideal gas, Pideal, is related to the experimentally measured pressure, Preal by the equation
Constant 'a' is measure of intermolecular interaction between gaseous molecules that gives rise to non-ideal behavior. It depends upon how
frequently any two molecules approach each other closely. Another correction concerns the volume occupied by the gas molecules. In the ideal gas equation, V represents the volume of the container. However, each molecule does occupy a finite, although small, intrinsic volume, so the effective volume of the gas becomes (V - nb), where n is the number of moles of the gas and b is a constant. The term nb represents the volume occupied by gas particles present in n moles of the gas. Having taken into account the corrections for pressure and volume, we can rewrite the ideal gas equation as follow
At relatively high pressures, the van der Waals' equation of state reduces to
For non-zero value of force of attraction between gas molecules at large volume, gas equation will be:
The van der Waals' constant 'a' for CO2 gas is greater than that of H2 gas. Its mean that the
So CO2 gas can be more easily liquified.