The temperature dependence of free energy

It is apparent from the relationship that defines the free energy change in terms of the enthalpy and entropy changes of the system that ΔG depends on the temperature in Kelvin.


The direction in which ΔG changes with temperature depends on the sign of ΔS because
 

• if ΔS is positive,
  the –TΔS contribution to ΔG is negative and
  ΔG becomes more negative at higher T
• if ΔS is negative,
  the –TΔS term is positive
  and ΔG becomes more positive at higher T

Because for reactions involving gases, it is often possible to predict the sign of ΔS, for these same reactions it is also possible to predict how ΔG changes with temperature.

---

The temperature above which at a reaction will become spontaneous can be calculated using the relationship above if the enthalpy change and the entropy change is known.