Chapter 5

Free Energy and Work Function

5.a.1.   Entropy as a Criterion for Spontaneity

In an isolated system the internal energy is constant and any spontaneous change is accompanied by an increase in entropy. The system being isolated, cannot transfer its energy in the form of work. In order that no work of expansion occurs, it is seen that the volume of an isolated system should also be constant. Thus an isolated system may be defined as one of constant U and V and so any spontaneous change is accompanied by an increase in entropy. If we take the system and the surroundings together, we can consider it to be an isolated system and apply the criterion that the entropy of the universe must increase for any spontaneous process. Alternatively, ...

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