Reactions proceed until composition of rxn mixture (given by Q)
corresponds to minimum Gibbs Free Energy.

ΔG changes throughout reaction because Q changes.
ΔG = ΔG0 + RT ln Q

              

ΔG0 < 0
K > 1
Product–favored at equilibrium
              ΔG0 > 0
              K < 1
              Reactant–favored at equilibrium