Chapter U6.122, Problem 3E

Interpretation Introduction

Interpretation: The effect of adding ammonia, ${\text{NH}}_{\text{3}}\text{(aq)}$ to the following equilibrium mixture needs to be explained:

  ${\text{Cu(H}}_{\text{2}}{\text{O)}}_{\text{6}}^{\text{2+}}{\text{(aq) + 6NH}}_{\text{3}}\text{(aq) }\rightleftharpoons {\text{ Cu(NH}}_{\text{3}}{\text{)}}_{\text{6}}^{\text{2+}}{\text{(aq) + 6H}}_{\text{2}}\text{O(aq)}$

Concept introduction: According to LeChatlier's principle, when a dynamic equilibrium is subjected to a change in either concentration or temperature or pressure, then the position of equilibrium will shift in such a direction that it nullifies the change.

For example:

  $\text{A + B }\rightleftharpoons \text{ C}$ is a system at equilibrium.

If concentration of A is increased by adding some more amount of A at equilibrium, then left side concentration is increasing, so to nullify this change, equilibrium shifts towards right side. Hence, forward reaction or formation of C is favoured in this case.

Answer to Problem 3E

The concentration of reactants will decrease and that of products will increase and hence, resulting in increase in ${\text{K}}_{\text{eq}}$ value.

Explanation of Solution

The given equilibrium mixture equation is:

  ${\text{Cu(H}}_{\text{2}}{\text{O)}}_{\text{6}}^{\text{2+}}{\text{(aq) + 6NH}}_{\text{3}}\text{(aq) }\rightleftharpoons {\text{ Cu(NH}}_{\text{3}}{\text{)}}_{\text{6}}^{\text{2+}}{\text{(aq) + 6H}}_{\text{2}}\text{O(aq)}$

The addition of ammonia, ${\text{NH}}_{\text{3}}\text{(aq)}$ to the above equilibrium mixture means that the concentration of the reactantincreases. Now, according to LeChatlier's principle, the equilibrium will shift in forward direction (product side as the concentration of reactant is increasing) in order to nullify the change. Thus, on adding ammonia, ${\text{NH}}_{\text{3}}\text{(aq)}$ to the given equilibrium equation, the concentration of reactants will decrease and that of products will increase and hence, resulting in increase in ${\text{K}}_{\text{eq}}$ value.