Chapter 20, Problem 14STP

Interpretation Introduction

Interpretation:

The value of equilibrium constant for a given reaction is to be calculated.

Concept introduction:

The equilibrium constant is the ratio of molar concentration of products to the reactants. It is represented by ${\text{K}}_{\text{eq}}$.

The formula is given as: there is a chemical reaction

$\text{ aA+Bb}\rightleftharpoons \text{cC+dD }$

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

Where, $\left[\text{C}\right]$ and $\left[\text{D}\right]$ = molar concentration of products

$\left[\text{A}\right]$ and $\left[\text{B}\right]$ = molar concentration of reactants

a, b, c, and d are number of molecules.

Answer to Problem 14STP

Correct answer: C is correct

C. $\begin{array}{l}\text{Keq = }\frac{{\left[{\text{H}}_{\text{2}}\text{O}\right]}^{\text{2}}}{{\left[{\text{H}}_{\text{2}}\text{S}\right]}^{\text{2}}\left[{\text{SO}}_{\text{2}}\right]}\\ \end{array}$

Explanation of Solution

Reason for correct option:

Given information: the given reaction is

${\text{2H}}_{\text{2}}\text{S}\left(\text{g}\right){\text{+SO}}_{\text{2}}\left(\text{g}\right)\rightleftharpoons \text{3S}\left(\text{l}\right){\text{ + 2H}}_{\text{2}}\text{O}\left(\text{g}\right)$

According to the Le Chatelier’s principle, the equilibrium constant is the ratio of molar concentration of products to the molar concentration of reactants. It is represented by $\text{Keq}$.

$\begin{array}{l}\text{Keq = }\frac{{\left[{\text{H}}_{\text{2}}\text{O}\right]}^{\text{2}}{\left[\text{S}\right]}^{\text{3}}}{{\left[{\text{H}}_{\text{2}}\text{S}\right]}^{\text{2}}\left[{\text{SO}}_{\text{2}}\right]}\\ \end{array}$

Because the given reaction is a heterogeneous reaction in which product and reactants are in different phase. For heterogeneous reactions the concentration of pure liquids is unity. So, we get

$\begin{array}{l}\text{Keq = }\frac{{\left[{\text{H}}_{\text{2}}\text{O}\right]}^{\text{2}}}{{\left[{\text{H}}_{\text{2}}\text{S}\right]}^{\text{2}}\left[{\text{SO}}_{\text{2}}\right]}\\ \end{array}$

Conclusion

Reasons for incorrect options:

1. Not matches with calculated value.
2. Not matches with calculated value.
3. Not matches with calculated value.