Chapter 17.3, Problem 6RQ

Interpretation Introduction

Interpretation: Equilibrium expression for given reaction must be written.

Concept introduction: When the rate at which forward and backward reaction occur become equal such that concentration of reactants and products remains to be constant, that state is described as equilibrium. It is indicated by double sided arrow $\rightleftharpoons$ . It can be physical or chemical in nature.

For an equilibrium reaction:

  $a\text{A}+b\text{B}\rightleftharpoons c\text{C}+d\text{D}$

The expression for equilibrium constant is:

  $K=\frac{{\left[\text{C}\right]}^c{\left[\text{D}\right]}^d}{{\left[\text{A}\right]}^a{\left[\text{B}\right]}^b}$

Where,

  $K$ is equilibrium constant.

  $\left[\text{A}\right]$ and $\left[\text{B}\right]$ are reactant concentrations for A and B.

  $\left[\text{C}\right]$ and $\left[\text{D}\right]$ are product concentrations for C and D.

a, b, c and d are coefficients of reactants.

Answer to Problem 6RQ

Equilibrium expression for given reaction: $\text{AgCl}\left(s\right)\rightleftharpoons {\text{Ag}}^{+}\left(aq\right)+{\text{Cl}}^{-}\left(aq\right)$ is:

  $K_{sp}=\left[{\text{Ag}}^{+}\right]\left[{\text{Cl}}^{-}\right]$

Explanation of Solution

Concentration of Pure solids and liquids are never incorporated in the expression for equilibrium as their concentration remains to be unchanged through the reaction.

For reaction that involves sparingly soluble salt such as:

  $\text{AgCl}\left(s\right)\rightleftharpoons {\text{Ag}}^{+}\left(aq\right)+{\text{Cl}}^{-}\left(aq\right)$

Equilibrium constant is: $K_{sp}=\left[{\text{Ag}}^{+}\right]\left[{\text{Cl}}^{-}\right]$ where $K_{sp}$ is called solubility product.

Conclusion

Equilibrium expression for given reaction: $\text{AgCl}\left(s\right)\rightleftharpoons {\text{Ag}}^{+}\left(aq\right)+{\text{Cl}}^{-}\left(aq\right)$ is:

  $K_{sp}=\left[{\text{Ag}}^{+}\right]\left[{\text{Cl}}^{-}\right]$