Chemical Equilibrium for a Non-ideal Gas

As mentioned above, activities are correctly represented by fugacities and not by partial pressures. Hence, the correct form of Eq. (22) is  

When dealing with an ideal mixture of gases (that do not behave ideally themselves), the fugacity of gas X is given by 

If we make the same assumptions as above, i.e. constant total pressure and a stoichiometric gas mixture (N2 -r 3H2 at the start), we obtain 

Please note that the correction corresponds to introducing a corrected equilibrium constant K(T)/X . The correction has hardly any influence on the mole fraction of ammonia in the mixture at low pressures, but for ptot = 100 bar and higher the correction becomes significant. The results are presented in the last column of Tab. 2.4 and in Fig. 2.1. It should be noted that correction procedures exist for cases where the mixture does not behave ideally, but this goes beyond the scope of the present treatment. 

---