Chemical Equilibrium in Systems of Variable Composition

We can apply the criterion of equilibrium expressed in Equation (9.17) to chemically reacting systems. Consider the reaction 

However, the various dn , in Equation (9.48) are not independent, but, in view of the stoichiometry of the reaction of Equation (9.47), they must be related as follows  

As reactants disappear and products appear in the reaction, the corresponding dn s in Equation (9.49) have opposite signs. In view of the series of equalities in this equation, let us define a quantity d such that 

If Equation (9.52) is integrated with respect to from = 0to =l at constant values of the chemical potentials (fixed composition of the reacting mixture), then we obtain, at equilibrium, 

The concept of escaping tendency also can be applied to the chemical reaction in Equation (9.47). At equilibrium, from Equation (9.54), we can say that the sum of the escaping tendencies of the reactants is equal to the sum of the escaping tendencies of the products. 

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