# Gibbs Energy

## Read in this section

### Properties of the Gibbs Energy – Temperature dependence

On the previous page, we derived an expression which gives us a relationship between the Gibbs energy and temperature.

### Properties of the Gibbs Energy – Pressure dependence

We start with the definition of the Gibbs energy, G = H – TS . When the system undergoes a change of state, we may write, for any general change.

### Comments on the Gibbs Energy

The criterion for spontaneous change dG £ 0 may be very simply expressed in words as a tendency of the Gibbs energy to tend to a minimum value. i.e. reactions are only spontaneous in the direction of decreasing Gibbs energy.

### The Gibbs Energy

Entropy is the fundamental basis for assigning the direction of spontaneous change, but to use it we must consider the entropy changes of both the system and the surroundings, which is somewhat inconvenient.