The #"Gibbs Free Energy"# includes an entropy term, and an enthalpy term. The #"Gibbs Free Energy"# is the single unequivocal criterion for the spontaneity of chemical change. If #DeltaG^@# #<0#, the reaction is spontaneous; if #DeltaG^@# #=0#, the reaction is at equilibrium; If #DeltaG^@# #>0#, the reaction is non-spontaneous.
#DeltaG^@# values have been tabulated for many substances, and can be used to assess many chemical reactions.........
Also, importantly, #DeltaG^@=-RTln{K_"eq"}# (and again here #DeltaG^@# must be negative to give #K_"eq">0#.