Question

What is the value of $∆\mathrm{G}$ when a system is at equilibrium?

Answer 1

Gibbs free energy: Gibbs free energy is that thermodynamic quantity the decrease in whose value during a process is equal to the maximum possible useful work that can be obtained from the system.

Mathematically it can be represented as follows:

$∆\mathrm{G}=∆\mathrm{H}-\mathrm{T}∆\mathrm{S}$;

where $∆\mathrm{G}$ is the change in Gibbs free energy, T is the temperature,$∆\mathrm{H}$ is the change in enthalpy, $∆\mathrm{S}$change in entropy.

The usefulness of Gibbs free energy:

• The value of change in Gibbs free energy helps us to predict the nature of the reaction.

$$\begin{gathered} ∆\mathrm{G}=-\mathrm{ve},\mathrm{reaction}\mathrm{is}\mathrm{spontaneous} \\ ∆\mathrm{G}=+\mathrm{ve},\mathrm{reaction}\mathrm{is}\mathrm{non}-\mathrm{spontaneous} \\ ∆\mathrm{G}=0,\mathrm{reaction}\mathrm{is}\mathrm{in}\mathrm{equilibrium} \end{gathered}$$

Hence, the change in Gibbs free energy is zero at equilibrium.