At high temperature and low pressure real gas acts as an ideal gas and obey p V=nRT relation. for real gases, (p− V2n2a)(V−nb)=RT 
Van der Waals isotherms demonstrates the relationship between pressure, volume, and temperature based on the van der Waals model. The constants a and b have positive values and are specific to each gas. The higher the value of a, the greater the attraction between molecules and the more easily the gas will compress. The b term represents the excluded volume of the gas or the volume occupied by the gas particles. The van der Waals equation becomes the Ideal Gas Law as these two correction terms approach zero.