Chemical Equilibrium and the Mass Action Expression

Mathematically, this is taken into account by appreciating that the driving force for any reaction is composed of two terms The first is how likely one expects the reaction to occur under standard conditions, and the second factor takes into account the fact that the reactants may or may not be in their standard states. In other words, it can be shown (App. 5A) that the driving force AGrxn for reaction is given by 

At equilibrium, AGrxn = 0, and Eq. (5.27) simplifies to the well-known result 

Before one proceeds further, it is instructive to dwell briefly on the ramifications of Eq. (5.27). First, this equation says that if the reactants 

K = 1 and AGj-xn = AGrxnj which is how AGrxn was defined in the first place. The other extreme occurs when the driving force for the reaction is zero, that is, A rsn = 0, which by definition is the equilibrium state, in which case Eq. (5.29) applies. 

It is worth noting that for the generalized reaction aA T hB cC T dD the equilibrium constant is given by 

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