Chapter 17, Problem 25A

Interpretation Introduction

Interpretation: The reason due to which the position of a heterogeneous equilibrium does not depend on the amounts of the pure solids or pure liquids reactant or product presents needs to be explained.

Concept introduction:Heterogeneous equilibrium can be defined as equilibrium where the components (reactants and products) are present in different phases.

Aqueous solution of a solid calcium hydroxide is an example of heterogeneous equilibrium. Solid calcium hydroxide is in equilibrium with its constituent ions.

The equilibrium dissociation reaction: $Ca{\left(OH\right)}_2\left(s\right)\rightleftharpoons C{a}^{2+}\left(aq\right)+2O{H}^{-}\left(aq\right)$

Answer to Problem 25A

The concentration of pure solids and liquids do not change over the course of reaction.

Explanation of Solution

Equilibrium expressions used to determine the changes in concentration that happens as the reaction approaches equilibrium. Aqueous solutions and gases change their concentrations considerably during the course of reaction. On the other hand, pure liquids and solids do not change their concentration much as reaction moves towards equilibrium since they are present in large excess.

Hence pure liquids and solids are not included in equilibrium expression equation.

Conclusion

The concentration of pure solids and liquids do not change over the course of reaction.