Isotherms ConstantIdeal Gas Region Pe-. MPa Region R h 17K Boiling. Observe that inert gases like Helium have a low value of a as one would expect since such gases do not interact very strongly, and that large molecules like Freon have large values of b There are many more equations of state that are even better approximation of real gases than the van der Wall equationl Observe that inert gases like Helium have a low value of a as one would expect since such gases do not interact very strongly, and that large molecules like Freon have large values of b. l There are many more equations of state that are even better approximation of real gases than the van der Wall equation