Explain the use of the equilibrium constant to predict the extent of a reaction with an example.

(N/A) The numerical value of the equilibrium constant $(K_{c})$ for a reaction indicates the extent of the reaction,but it does not provide information about the rate of the reaction.
The magnitude of $K_{c}$ or $K_{p}$ is directly proportional to the concentrations of products and inversely proportional to the concentrations of the reactants. $A$ high value of $K$ indicates that the concentration of products is high,while a low value of $K$ indicates that the concentration of products is low.
Value of $K \propto \text{[Products]} \propto \frac{1}{\text{[Reactants]}}$
The following generalizations describe the composition of equilibrium mixtures:
$(a)$ If $K_{c} > 10^{3}$: Products predominate over reactants; i.e.,if $K_{c}$ is very large,the reaction proceeds nearly to completion. Examples:
$(i)$ The reaction $H_{2(g)} + \frac{1}{2} O_{2(g)} \rightleftharpoons H_{2}O_{(g)}$ at $500 \ K$ has a very large equilibrium constant,$K_{c} = 2.4 \times 10^{47}$.
$(ii)$ $H_{2(g)} + Cl_{2(g)} \rightleftharpoons 2 HCl_{(g)}$ at $300 \ K$ has a very large $K_{c} = 4.0 \times 10^{31}$.
$(iii)$ $H_{2(g)} + Br_{2(g)} \rightleftharpoons 2 HBr_{(g)}$ at $300 \ K$ has a very large $K_{c} = 5.4 \times 10^{18}$.