If a reaction is favorable for both enthalpy (H < 0 ) and entropy (S > 0) changes, then the reaction will be SPONTANEOUS (G < 0 ) at any temperature.
If a reaction is unfavorable for both enthalpy (H > 0 ) and entropy (S < 0 ) changes, then the reaction will be NON-SPONTANEOUS (G > 0 ) at any temperature.
If a reaction is favorable for only one of either entropy or enthalpy, the standard-state free energy equation must be used to determine whether the reaction is spontaneous or not.
For non-standard-state conditions (P ≠ 0.1 MPa; concentrations ≠ 1 M), values of H and S for the actual reaction conditions must be calculated and used to determine G and Keq.