3.1.8.2 Gibbs free-energy change, ∆G, and entropy change, ∆S

• ∆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.
  • Physical changes: Changes in state
  • Chemical changes: Increase in number of moles
• 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.
• MUST CONVERT UNITS for ENTROPY CHANGE FROM JK-1mol into KJ K-1 mol-1!
• • Elements in their standard states do not have zero entropy.
  • Only perfect crystals at absolute zero (T = 0 K) will have zero ∆S entropy.