Write the uses of equilibrium constant.

(N/A) The equilibrium constant $(K_c)$ is used for the following purposes:
$1$. Predicting the direction of the reaction: By calculating the reaction quotient $(Q_c)$,we can compare it with $K_c$. If $Q_c < K_c$,the reaction proceeds in the forward direction. If $Q_c > K_c$,the reaction proceeds in the reverse direction. If $Q_c = K_c$,the reaction is at equilibrium.
$2$. Calculating equilibrium concentrations: If the equilibrium constant and the initial concentrations of the reactants are known,the concentrations of all species at equilibrium can be calculated using the equilibrium expression.