Gibbs free energy reaction progress

The basic criterion for equilibrium with respect to a given chemical reaction is that the Gibbs free energy change associated with the progress of the reaction be zero. 

The transition state is a short-lived entity and/or state positioned at the maximum in the potential energy-reaction coordinate relationship depicted in Figure 8.1. The term reaction coordinate loosely describes the progress of the reaction from reactants to products, so that contributions to AG (Gibbs free energy) in Figure 8.1 come from... 

The Gibbs free energy is the thermodynamic state function most naturally suited to describing the progress of chemical reactions at constant T and P. It provides the basis for predicting the equilibrium composition of the reaction mixture... 

Whether or not kinetics limits reaction progress is sometimes (but not always) related to the magnitude of AG,. Reactions with Gibbs free energies of tens of kilocalories are more likely to go spontaneously than are those with free energies of a few hundred calories or less. 

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