Explain chemical equilibrium and free Gibbs energy change by $\Delta G$.

(N/A) The value of $K_{c}$ indicates the ratio of product and reactant concentrations at equilibrium,but it does not describe the rate of the reaction. The value of $K_{c}$ does not indicate the time required to attain equilibrium; this is explained by thermodynamics. Gibbs free energy $(\Delta G)$ is used to predict the spontaneity of a reaction.
$(i)$ $\Delta G < 0$: If $\Delta G$ is negative,the reaction is spontaneous. The reaction proceeds in the forward direction,and products are formed from reactants as the system moves toward a lower energy state.
$(ii)$ $\Delta G > 0$: If $\Delta G$ is positive,the reaction is non-spontaneous in the forward direction. The reaction will not occur spontaneously as the system is not thermodynamically favored.
$(iii)$ $\Delta G = 0$: If $\Delta G$ is zero,the system is at chemical equilibrium.