At low pressure and high temperature van der Waals real gas acts as ideal gas and observed to obey PV=nRT relation. At very low pressure when the gas-volume is quite large the space occupied by the molecules themselves becomes negligible comparatively and because the molecules are then far apart, the force of mutual attraction becomes too feeble, the real gas would satisfy the postulates of kinetic theory. As temperature is raised, the volume of the gas increases and we can consider (P+
n2a
V2
) term as P and at low pressure (V−nb) term as V (P+
n2a
V2
)(V−nb)=nRT (van der Waals' equation) The gas equation becomes PV=nRT This is ideal gas equation.