∆G = ∆H - T∆S

1. If ΔH is negative and ΔS is positive, the reaction will be spontaneous at all temperatures.

2. If ΔH is positive and ΔS is negative, the reaction will be not be spontaneous at any temperature.

3. If ΔH is negative and ΔS is negative, the reaction will be spontaneous at low temperatures.

4. If ΔH is positive and ΔS is positive, the reaction will be spontaneous at high temperatures.

Or consult this table:

∆H........ ∆S........ ∆G ......... conditions

..-........... + .......... - ........... at all temperatures

..+ ......... - ........... + ........... at all temperatures

..-........... - ........... - ............ at low temperatures

..+ ......... + .......... - ............ at high temperatures