Question

The equilibrium constant for the given reaction \[{{H}_{2}}+{{I}_{2}}\rightleftharpoons 2HI~\] is correctly given by expression.
A. \[Kc=\frac{[HI]}{[{{H}_{2}}][{{I}_{2}}]}\]
B. \[Kc=\frac{[2HI]}{[{{H}_{2}}][{{I}_{2}}]}\]
C. \[Kc=\frac{{{[HI]}^{2}}}{[{{H}_{2}}][{{I}_{2}}]}\]
D .\[Kc=\frac{[{{H}_{2}}][{{I}_{2}}]}{{{[HI]}^{2}}}\]

Answer 1

Hint: To solve this question we have to know about equilibrium constant. In an equilibrium reaction the rate constant of the reaction is given as the ratio of concentration of product to the concentration of reactant. Any coefficient of the reactant or product is used as the power of the concentration.

Complete Step by Step Solution:
The given reaction is \[{{H}_{2}}+{{I}_{2}}\rightleftharpoons 2HI~\].
In this reaction one mole of hydrogen gas reacts with one mole of iodine gas to produce two moles of hydrogen iodide gas. It is a unimolecular reaction as the change in number of moles is zero. It is an equilibrium reaction as the product can also decompose to give back the reactants hydrogen gas and iodine gas.

In an equilibrium reaction the rate constant of the reaction is given as the ratio of concentration of product to the concentration of reactant. Any coefficient of the reactant or product is used as the power of the concentration.

The equilibrium constant of the above equilibrium reaction is given as follows:
\[Kc=\frac{{{[HI]}^{2}}}{[{{H}_{2}}][{{I}_{2}}]}\]
Thus the correct option is C.

Note: An equilibrium reaction is that reaction where there a equilibrium exist between the reactants and products of the reaction. Here the reaction can proceed in both the forward and backward directions that means reactants reacts to give product and again product can also break down into the corresponding reactants.