### What is Gibbs Energy ?

Where,

\(\triangle G_{sys}\)

\(\triangle H_{sys}\)

\(\triangle S_{sys}\)

\( T \)

Where,

\(\triangle S_{total}\)

\(\triangle S_{sys}\)

\(\triangle S_{surr}\)

\(\triangle S_{total}\)

\(\triangle H_{surr}\)

As discussed earlier, for the spontaneity of a process, Stotal > 0. Above equation becomes,

\(T\triangle S_{sys} – \triangle H_{sys} >0\)

\(\triangle H_{sys} – T\triangle S_{sys} <0\)

Above equation can be related to Gibbs equation as,

\(\triangle G_{sys} < 0\)

On the basis of above equation we can infer:

- \(\triangle G_{sys} < 0\)
, the process is spontaneous - \(\triangle G_{sys} > 0\)
,, the process is non-spontaneous

### Spontaneity Of A Process

Gibbs equation helps us to predict the spontaneity of reaction on the basis of enthalpy and entropy values directly. When the reaction is exothermic, enthalpy of the system is negative making Gibbs free energy negative. Hence we can say that all exothermic reactions are spontaneous.

In case of endothermic reactions, when enthalpy of the system is positive, the process is spontaneous under two conditions:

- Temperature is very high to make the Gibbs energy value negative
- Entropy change is very high to make the Gibbs free energy negative.

**can**occur not necessarily if a reaction

**will**occur. For example, the conversion of diamond to graphite is a spontaneous process at Standard Temperature and Pressure (STP) but it is a slow process. It will take years for the transformation to occur.

For detailed discussions on spontaneity of a process on the basis of Gibbs free energy change, check out Byju’s-The Learning App.

**Practise This Question**