Determining Spontaneity Using ΔH, ΔS, and ΔG:

ΔH°

Enthalpy change.

ΔS°

Entropy change.

T

Temperature.

ΔG°

Gibbs free energy change.

Spontaneous

A reaction that occurs without external input.

What are the conditions when ΔH° is positive and ΔS° is negative?

Always non-spontaneous.

What are the conditions when ΔH° is negative and ΔS° is positive?

Always spontaneous.

What occurs when ΔH° and ΔS° are both positive?

Spontaneous at high T if ΔG° = -, non-spontaneous at low T if ΔG° = +.

What are the spontaneity conditions when ΔH° and ΔS° are both negative?

Spontaneous at low T if ΔG° = -, non-spontaneous at high T if ΔG° = +.

What does it mean when ΔG° is negative?

The reaction is spontaneous.

What does it mean when ΔG° is positive?

The reaction is non-spontaneous.