2. Relationship between ΔG o and K eq : In a reaction A → B, a point of equilibrium is reached at which no further net chemical change takes place—that is, when A is being converted to B as fast as B is being converted to A. In this state, the ratio of [B] to [A] is con- stant, regardless of the actual concentrations of the two compounds:

Keq = [B]eq/[A]eq

where K eq is the equilibrium constant, and [A] eq and [B] eq are the concentrations of A and B at equilibrium. If the reaction A B is allowed to go to equilibrium at constant temperature and pres- sure, then at equilibrium the overall free energy change (ΔG) is zero. Therefore, where the actual concentrations of A and B are equal to the equi- librium concentrations of reactant and product [A] eq and [B] eq , and their ratio as shown above is equal to the K eq. Thus,

∆G = ∆Go - RTlnKeq

This equation allows for some simple predictions:

If Keq = 1, then ∆Go = 0 and A <--> B
If Keq > 1, then ∆Go < 0 and A <---->>>> B
If Keq < 1, then ∆Go > 0 and A <<<<------> B