Chemical equilibrium in a mixture of real gases

If the corresponding algebra were carried out for real gases using Eq. (10.48), the equation equivalent to Eq. (11.41) is 

For real gases, it is Kf rather than K that is a function of temperature only. 

It is sometimes advantageous to express the equilibrium constant for gaseous systems in terms of either mole fractions, or concentrations, q, rather than partial pressures. The partial pressure, pi, the mole fraction, and the total pressure, p, are related by Pi = Xip. Using this relation for each of the partial pressures in the equilibrium constant, we obtain from Eq. (11.41) 

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