van der Waals' equation for calculating the pressure of a non ideal gas isP+an2V2(V−nb)=nRTvan der Waals' suggested that the pressure exerted by an ideal gas, Pideal, is related to the experimentally measured pressure, Preal by the equationPideal =Preal +an2V2 ↑ ↑   observed correction  pressure term      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 followP+an2V2(V−nb)=nRT corrected  corrected  pressure  volume At relatively high pressures, the van der Waals' equation of state reduces toFor 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