`DeltaG` is net energy available to do useful work and is thus a measure of " free energy".Show mathematically that `DeltaG` is a measure of free energy.Find the unit of `DeltaG`.If a reaction has positive enthalpy change and positive entropy change, under what condition will the reaction be spontaneous?

Explanation

(i) Refer to art
(ii)As - `DeltaG = w_("useful"), ` therefore, `DeltaG` has the same units those of work viz. joule.
(iii) `DeltaG = DeltaH- T DeltaS`. If `DeltaH = +ve` and` DeltaS = +ve` , then `DeltaG` will be negative, i.e., process will be spontaneous only when `T DeltaS gt DeltaH`in magnitude , which will be so when temperature T is high.