Chapter 17, Problem 17.1P

Interpretation Introduction

Interpretation:

The effect on equilibrium constant and concentration of reactants and products at equilibrium has to be explained, when the reaction conditions are altered to increase the rate of forward reaction.

Concept Introduction:

Le Chatelier principle states that, whenever a system at equilibrium is disturbed, the system will undergo reactions and try to cancel that effect and reattain equilibrium. Here the disturbance means change in concentration of any of the component, change in temperature, pressure or volume.

Equilibrium constant (K) is the equilibrium ratio of concentration/partial pressure of product to reactant in which the stoichiometric term raised to the power of each component’s concentration or partial pressure. It has a particular value at a particular temperature.

Consider a reaction, a moles of A gives b moles of B as follows,

$\text{a A }\rightleftharpoons \text{ b B}$

The equilibrium constant for this reaction can be written as follows,

$\text{K = }\frac{{\text{[B]}}_{\text{eq}}^{\text{b}}}{{\text{[A]}}_{\text{eq}}^{\text{a}}}$

Where,

    $\begin{array}{l}{\text{[A]}}_{\text{eq}}^{}\text{= equilibrium concentration of A}\\ {\text{[B]}}_{\text{eq}}^{}\text{ = equilibrium concentration of B}\\ \text{ a = stoichiometric co-efficient of A}\\ \text{ b = stoichiometric co-efficient of A}\end{array}$

Explanation of Solution

According to Le-Chatelier principle, whenever a system is disturbed the system will try to nullify the effect and try to reach equilibrium.  More products can be obtained when the rate of forward reaction is greater than the rate of reverse reaction. This can be achieved by increasing the concentration of reactant, removing the product from the system or changing the temperature.

If the rate of forward reaction increased due to change in concentration, either by increasing the concentration of reactant or removing the product from the system. But the overall ratio of concentration of product to reactant remains same. So, equilibrium constant will not change.

If more products are obtained due to change in temperature then, rate of both forward and backward reaction changes. So equilibrium constant also changes. K value increases due high rate of forward reaction than reverse reaction. According to the equation below, the equilibrium constant K increases since large amount of product and small less amount of reactant present in the system.

$\text{K = }\frac{{\text{[Product]}}_{}^{}}{{\text{[Reactant]}}_{}^{}}$