The phase rule for chemically reacting systems

Because the presence of chemical reactions introduces additional constraints on a system, we need to reconsider the Gibbs phase rule. In tlie absence of chemical reactions, the number of degrees of freedom / in a system is given by 

For a system with chemical reactions, there is one addition equation (see Eq. (12.7)) for every independent chemical reaction in tlie system. The presence of chemical reactions, therefore, imposes constraints on a system, which decrease its degrees of freedom. The phase rule now becomes  

---