top of page
new sciteach chem small.png

Gibbs Free-Energy and Entropy Change




AQA Content

Calculate entropy changes from absolute entropy values
Use the relationship ∆G = ∆H – T∆S to determine how ∆G varies with temperature
Use the relationship ∆G = ∆H – T∆S to determine the temperature at which a reaction becomes feasible.

Specification Notes

∆H, whilst important, is not sufficient to explain feasible change.
The concept of increasing disorder (entropy change, ∆S).

∆S accounts for the above deficiency, illustrated by physical changes and chemical changes.
The balance between entropy and enthalpy determines the feasibility of a reaction given by the relationship:
∆G = ∆H – T∆S (derivation not required).
For a reaction to be feasible, the value of ∆G must be zero or negative.



bottom of page