Equilibrium constants and molecular partition functions

The fact that tliermodynamic constants and, in particular, Gibbs energies can be expressed using partition functions, this must be the same for equilibrium constants. 

We are going to express the ecpiihbrium constant of a reaction using the partition functions of the reactants and products. 

A chemical reaction between reactants Ar giving products Ap can be written in the form  

This equation uses stoichiometric algebraic numbers positive for a reaction product and negative for a reactant. 

According to relation [5.46] and, by taking into account the expression of pressure given by relation [5.44], we can write the Gibbs energy of component in the form  

---