Question

For a spontaneous process, the change in Gibbs function is equal to the:

• A. heat content of the system
• B. entropy change of the system
• C. work of expansion
• D. useful work

Answer 1

The correct option is D useful work

Change in Gibbs function= $△G$

$△G$ is the net energy available to do useful work and is thus a measure of free energy.

For a spontaneous process, $△G$ is negative i.e; $△G<0$

This is because, for a spontaneous process,

$△S_{total}>0$, So

$T△S_{sys}-△H_{sys}>0$

$\Rightarrow (△H_{sys}-T△S_{sys})<0$

So, $△G=△H-T△S<0$.