Unit 9: Applications of Thermodynamics - AP Chemistry Notes

Gibbs Free Energy (G)

Indicates the spontaneity of a reaction.

What does a G < 0 indicate?

The reaction is spontaneous.

What does a G > 0 indicate?

The reaction is non-spontaneous.

Entropy (S)

Measure of disorder or randomness in a system.

What is the equation for Gibbs Free Energy?

G = H - TS

Exothermic reaction

H < 0 (releases heat).

Endothermic reaction

H > 0 (absorbs heat).

Standard Free Energy Change (G)

G = -RTlnK, determines spontaneity at standard conditions.

If G is negative

K > 1 and products are favored

What happens to the reaction if Q < K?

The reaction shifts to the right (forward).

Coupled Reactions

Reactions that are linked so that one non-spontaneous reaction is driven by a spontaneous one.

What factors influence spontaneity besides G?

H and S.

What is the relationship of S to phase changes?

Melting/boiling increases entropy; freezing/condensation decreases entropy.

If G is positive

K < 1 and reactants are favored