Chapter 17, Problem 34A

(a)

Interpretation Introduction

Interpretation: To describe the effect of increasing pressure by injecting hydrogen (product) on the equilibrium.

Concept introduction: According to Le Chatelier's principle if any stress is given to the equilibrium, it will shift in a direction to reduce the given stress. If change in concentration, pressure or temperature takes place at equilibrium, it will shift in the direction to undo the change or its effect.

Answer to Problem 34A

The reaction will move in the backward direction.

Explanation of Solution

According to Le Chatelier’s principle, if the pressure is increased, the direction of equilibrium will shift so as to reduce the pressure. Pressure is created when gas molecules collides with the sides of their container. The more the number of molecules in the container, the more will be the pressure. The system can decrease the pressure by reacting in such a way as to generate fewer molecules.

The concerned reaction: $\text{C}\left(\mathrm{g}\right)+{\text{H}}_{\text{2}}\text{O}\left(\mathrm{g}\right)\rightleftharpoons \text{CO}\left(\mathrm{g}\right)+{\text{H}}_{\text{2}}\left(\mathrm{g}\right)$

  $\begin{array}{c}\text{In this reaction change in the number of moles }\mathrm{\Delta }\mathrm{n}=(1+1)-(1+0)\\ =+1\end{array}$

So, here in the backward reaction moles of gas decreases. If pressure is increased reaction shifts in backward direction.

Pure solids and liquids are not included while calculating the change in number of moles because their concentration does not change considerably over the period of the reaction.

(b)

Interpretation Introduction

Interpretation: To describe the effect of removal of carbon monoxide on the equilibrium.

Concept introduction: According to Le Chatelier's principle if any stress is given to the equilibrium, it will shift in a direction to reduce the given stress. If change in concentration, pressure or temperature takes place at equilibrium, it will shift in the direction to undo the change or its effect.

Answer to Problem 34A

The reaction equilibrium will shift forward direction.

Explanation of Solution

The concerned reaction: $\text{C}\left(\mathrm{g}\right)+{\text{H}}_{\text{2}}\text{O}\left(\mathrm{g}\right)\rightleftharpoons \text{CO}\left(\mathrm{g}\right)+{\text{H}}_{\text{2}}\left(\mathrm{g}\right)$

The expression for equilibrium constant $\mathrm{K}=\frac{\left[\text{CO}\right]\left[{\text{H}}_{\text{2}}\right]}{\left[{\text{H}}_{\text{2}}\text{O}\right]}$

When $\text{CO}$ (product) is removed then the value of $\mathrm{K}$ will decrease as the concentration of $\text{CO}$ is in nominator. To maintain the value of $\mathrm{K}$ concentration of the products ( $\text{CO}$ and ${\text{H}}_{\text{2}}$ ) will increase. Hence, the reaction will shift towards right.

(c)

Interpretation Introduction

Interpretation: To describe the effect of addition of carbon on the equilibrium.

Concept introduction: According to Le Chatelier's principle if any stress is given to the equilibrium, it will shift in a direction to reduce the given stress. If change in concentration, pressure or temperature takes place at equilibrium, it will shift in the direction to undo the change or its effect.

Answer to Problem 34A

No effect on the equilibrium.

Explanation of Solution

The concerned reaction: $\text{C}\left(\mathrm{g}\right)+{\text{H}}_{\text{2}}\text{O}\left(\mathrm{g}\right)\rightleftharpoons \text{CO}\left(\mathrm{g}\right)+{\text{H}}_{\text{2}}\left(\mathrm{g}\right)$

The expression for equilibrium constant $\mathrm{K}=\frac{\left[\text{CO}\right]\left[{\text{H}}_{\text{2}}\right]}{\left[{\text{H}}_{\text{2}}\text{O}\right]}$

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.

Since solid carbon is added it will have no effect on the equilibrium.