Gibbs Free Energy

1. Gibbs Free Energy

2. Gibbs Free Energy • Gibbs free energy describes the temperature dependence of spontaneity.

3. Gibbs Free Energy • If DG is negative, the forward reaction is spontaneous. • If DG is 0, the system is at equilibrium. • If G is positive, the reaction is spontaneous in the reverse direction.

4. DG = SnDG (products)  SmG (reactants) f f Standard Free Energy Changes Analogous to standard enthalpies of formation are standard free energies of formation, G. f where n and m are the stoichiometric coefficients.

5. Free Energy Changes At temperatures other than 25°C, DG° = DH  TS How does G change with temperature?

6. There are two parts to the free energy equation: H— the enthalpy term TS — the entropy term The temperature dependence of free energy, then comes from the entropy term. TDSuniverse is defined as the Gibbs free energy, G. G=ΔH-TΔS to see how this equation relates to spontaneity, we dived everything by –T and get -ΔG= ΔH+ ΔS T T Free Energy and Temperature

7. Free Energy and Temperature

8. Free Energy and Equilibrium Under any conditions, standard or nonstandard, the free energy change can be found this way: G = G + RT lnQ (Under standard conditions, all concentrations are 1 M, so Q = 1 and lnQ = 0; the last term drops out.)

9. -G RT Free Energy and Equilibrium • At equilibrium, Q = K, and G = 0. • The equation becomes 0 = G + RT lnK • Rearranging, this becomes G = RT lnK or, K = e