Explain chemical equilibrium with an example of a chemical reaction.

(N/A) Example of synthesis of ammonia: The chemical equilibrium can be demonstrated in the synthesis of ammonia by Haber's process. In a series of experiments,Haber started with known amounts of dinitrogen and dihydrogen maintained at high temperature and pressure and at regular intervals determined the amount of ammonia present. He was successful in determining the concentration of unreacted dihydrogen and dinitrogen as well. This is shown in the following figure.
After some time,the composition of the reactants and products in the mixture remains constant. The amount of product and reactant does not change,and this is the equilibrium state. Equilibrium can be attained from both sides,whether we start the reaction by taking $H_{2(g)}$ and $N_{2(g)}$ to get $NH_{3(g)}$ or by taking $NH_{3(g)}$ and decomposing it into $N_{2(g)}$ and $H_{2(g)}$. Starting from the forward reaction to reach equilibrium:
$N_{2(g)} + 3H_{2(g)} \rightleftharpoons 2NH_{3(g)} \dots (I)$
And starting from the reverse reaction to reach equilibrium:
$2NH_{3(g)} \rightleftharpoons N_{2(g)} + 3H_{2(g)} \dots (II)$
$(B)$ Example of decomposition of hydrogen iodide $(HI)$: If we start with equal initial concentrations of $H_{2}$ and $I_{2}$,the reaction proceeds in the forward direction,and the concentrations of $H_{2}$ and $I_{2}$ decrease while that of $HI$ increases. After some time,the concentrations of all species $(H_{2}, I_{2}, HI)$ become constant,and the system reaches equilibrium.