Affinity in a one-phase ideal system

Let us first consider an ideal single phase system. For the affinity of a reaction occurring in this phase we have, from (6.22) and (7.1) 

This equation can be written in a simple form by setting 

If there are r simultaneous reactions occurring in the system, then Af=-Z T, p)-S v,, RTInx,. (7.31) 

The condition for chemical equilibrium is A == 0, so that we have immediately from (7.30)  

This simple equation, which interrelates the mole fractions of the components in the true equilibrium state, is essentially an expression of Guldberg and Waage s law of mass action. The quantity K T,p) is called the equilibrium constant of the reaction considered. 

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