Once you have started using the ideal gas equation of state its simplicity and utility are clear. In this section we describe some of the steps that can be taken to introduce the effects due to intermolecular interactions and finite size of gas molecules. While there are quite precise equations of state that can be used for engineering applications we will focus on a slightly less precise, but theoretically well motivated equation of state known as the van der Waal's equation of state. This equation of state includes the finite size using the hard sphere model. THis assumes that the gas behaves like a billiard ball. The potential energy is infinite when two gas molecules approach within an atomic or molecule diameter. Incidentally, much of the modeling of gases is based on monatomic gases in the noble gas series, Ne, Ar, Kr etc. The intermolecular interactions can also be modeled using a Lennard-Jones potential, which includes the attraction due to dispersion interactions (induced dipole-induced dipole interactions).
