The Gibbs free energy G is the thermodynamic potential that is minimized when a thermodynamic system reaches equilibrium. The free energy change of a reaction ?rxnG can be seen as the slope of a curve representing the progress of the transformation of reactants into products. It depends on the standard free energy ?rxnG°, the hypothetical change of unmixed reactants in standard conditions into unmixed products in standard conditions, to which a chemical term describing the changing ratio of activities is added.
a) Explain how the relation between ?rxnG and ?rxnG° is linked to the relation between the reaction quotient Q and the equilibrium constant K.
b) Consider the aqueous acid--base reaction where the reactants are ammonia and hydrogen cyanide, and the products are the cyanide and ammonium ions at 298,15 K: (i) What is the equilibrium constant K? (ii) In what direction would the the reaction proceed if reactants and products are in standard conditions? (iii) In what direction would the reaction proceed if [NH3]=[HCN]=0.57 M and [CN-] = [NH4+] = 10^-2 M?