Chapter 17, Problem 49A

Interpretation Introduction

Interpretation:

The balanced chemical equation and the equilibrium constant expression for an iron filling reversible reaction when steam is passed are to be explained.

Concept introduction:

The equilibrium constant is the ratio of concentration of products to the concentration of reactants and heterogeneous reaction is that in which the reactants and products are present in different phases. A reaction is balanced if number of molecules of reactants is equal to no. or molecules of products. We can say that the when a reaction satisfies the conservation law of mass is said to be a balanced equation.

Answer to Problem 49A

The balanced chemical equation of iron fillings when steam is passed is given as

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

The chemical equilibrium constant expression is given as

$\begin{array}{l}{\text{K}}_{\text{eq}}\text{=}\frac{\left[{\text{Fe}}_{\text{2}}{\text{O}}_{\text{3}}\left(\text{s}\right)\right]{\left[{\text{H}}_{\text{2}}\left(\text{g}\right)\right]}^{\text{3}}}{{\left[\text{Fe}\right]}^{\text{2}}{\left[{\text{H}}_{\text{2}}\text{O}\right]}^{\text{3}}}\\ \text{=}\frac{{\left[{\text{H}}_{\text{2}}\left(\text{g}\right)\right]}^{\text{3}}}{{\left[{\text{H}}_{\text{2}}\text{O}\right]}^{\text{3}}}\end{array}$

Here this reaction is a heterogeneous reaction, so the concentration of pure solids and liquids remains constant that is concentration of ${\text{Fe}}_{\text{2}}{\text{O}}_{\text{3}}$ and ${\left[\text{Fe}\right]}^{\text{2}}$ is unity.

Explanation of Solution

The balanced chemical equation of iron fillings when steam is passed is given as

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

A heterogeneous reaction is that in which reactants and product are in the different phases.

The given reversible reaction is

The equilibrium expression for the given reaction is

$\begin{array}{l}{\text{K}}_{\text{eq}}\text{=}\frac{\left[{\text{Fe}}_{\text{2}}{\text{O}}_{\text{3}}\left(\text{s}\right)\right]{\left[{\text{H}}_{\text{2}}\left(\text{g}\right)\right]}^{\text{3}}}{{\left[\text{Fe}\right]}^{\text{2}}{\left[{\text{H}}_{\text{2}}\text{O}\right]}^{\text{3}}}\\ \text{=}\frac{{\left[{\text{H}}_{\text{2}}\left(\text{g}\right)\right]}^{\text{3}}}{{\left[{\text{H}}_{\text{2}}\text{O}\right]}^{\text{3}}}\end{array}$

Here this reaction is a heterogeneous reaction, so the concentration of pure solids and liquids remains constant that is concentration of ${\text{Fe}}_{\text{2}}{\text{O}}_{\text{3}}$ and ${\left[\text{Fe}\right]}^{\text{2}}$ is unity.

Conclusion

The balanced chemical equation of iron fillings when steam is passed is given as

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

The chemical equilibrium constant expression is given as

$\begin{array}{l}{\text{K}}_{\text{eq}}\text{=}\frac{\left[{\text{Fe}}_{\text{2}}{\text{O}}_{\text{3}}\left(\text{s}\right)\right]{\left[{\text{H}}_{\text{2}}\left(\text{g}\right)\right]}^{\text{3}}}{{\left[\text{Fe}\right]}^{\text{2}}{\left[{\text{H}}_{\text{2}}\text{O}\right]}^{\text{3}}}\\ \text{=}\frac{{\left[{\text{H}}_{\text{2}}\left(\text{g}\right)\right]}^{\text{3}}}{{\left[{\text{H}}_{\text{2}}\text{O}\right]}^{\text{3}}}\end{array}$

Here this reaction is a heterogeneous reaction, so the concentration of pure solids and liquids remains constant that is concentration of ${\text{Fe}}_{\text{2}}{\text{O}}_{\text{3}}$ and ${\left[\text{Fe}\right]}^{\text{2}}$ is unity.