Chapter 7, Problem 7.93QP

(a)

Interpretation Introduction

Interpretation:

Addition of ${\text{PCl}}_{\text{5}}$ in the given equilibrium reaction results in increase, decrease, or no change in the amount of ${\text{PCl}}_{\text{3}}$ has to be predicted.

    ${\text{PCl}}_{\text{3}}(g)+{\text{Cl}}_{\text{2}}(g)\rightleftharpoons {\text{PCl}}_{\text{5}}(g)+\text{heat}$

Concept Introduction:

LeChatelier’s principle states that if a stress is applied on the system that is present at equilibrium, then the system will respond to the stress applied by altering the composition at equilibrium in a way to minimize the stress that is applied.

Explanation of Solution

Given equilibrium reaction is,

    ${\text{PCl}}_{\text{3}}(g)+{\text{Cl}}_{\text{2}}(g)\rightleftharpoons {\text{PCl}}_{\text{5}}(g)+\text{heat}$

When stress is applied on a system that is at equilibrium, the system adjusts itself to get relieved from the stress.  ${\text{PCl}}_{\text{5}}$ is present on right side of the equilibrium reaction.  Addition of ${\text{PCl}}_{\text{5}}$ results in shift of equilibrium to the left side as per LeChatelier’s principle.  This results in increased concentration of ${\text{PCl}}_{\text{3}}$.

(b)

Interpretation Introduction

Interpretation:

Addition of ${\text{Cl}}_{\text{2}}$ in the given equilibrium reaction results in increase, decrease, or no change in the amount of ${\text{PCl}}_{\text{3}}$ has to be predicted.

    ${\text{PCl}}_{\text{3}}(g)+{\text{Cl}}_{\text{2}}(g)\rightleftharpoons {\text{PCl}}_{\text{5}}(g)+\text{heat}$

Concept Introduction:

Refer part (a).

Explanation of Solution

Given equilibrium reaction is,

    ${\text{PCl}}_{\text{3}}(g)+{\text{Cl}}_{\text{2}}(g)\rightleftharpoons {\text{PCl}}_{\text{5}}(g)+\text{heat}$

When stress is applied on a system that is at equilibrium, the system adjusts itself to get relieved from the stress.  ${\text{Cl}}_{\text{2}}$ is present on left side of the equilibrium reaction.  Addition of ${\text{Cl}}_{\text{2}}$ results in shift of equilibrium to the right side as per LeChatelier’s principle.  This results in decreased concentration of ${\text{PCl}}_{\text{3}}$.

(c)

Interpretation Introduction

Interpretation:

Removal of ${\text{PCl}}_{\text{5}}$ in the given equilibrium reaction results in increase, decrease, or no change in the amount of ${\text{PCl}}_{\text{3}}$ has to be predicted.

    ${\text{PCl}}_{\text{3}}(g)+{\text{Cl}}_{\text{2}}(g)\rightleftharpoons {\text{PCl}}_{\text{5}}(g)+\text{heat}$

Concept Introduction:

Refer part (a).

Explanation of Solution

Given equilibrium reaction is,

    ${\text{PCl}}_{\text{3}}(g)+{\text{Cl}}_{\text{2}}(g)\rightleftharpoons {\text{PCl}}_{\text{5}}(g)+\text{heat}$

When stress is applied on a system that is at equilibrium, the system adjusts itself to get relieved from the stress.  ${\text{PCl}}_{\text{5}}$ is present on right side of the equilibrium reaction.  Removal of ${\text{PCl}}_{\text{5}}$ results in shift of equilibrium to the right side as per LeChatelier’s principle.  This results in decreased concentration of ${\text{PCl}}_{\text{3}}$.

(d)

Interpretation Introduction

Interpretation:

Decrease of temperature the given equilibrium reaction results in increase, decrease, or no change in the amount of ${\text{PCl}}_{\text{3}}$ has to be predicted.

    ${\text{PCl}}_{\text{3}}(g)+{\text{Cl}}_{\text{2}}(g)\rightleftharpoons {\text{PCl}}_{\text{5}}(g)+\text{heat}$

Concept Introduction:

Refer part (a).

Explanation of Solution

Given equilibrium reaction is,

    ${\text{PCl}}_{\text{3}}(g)+{\text{Cl}}_{\text{2}}(g)\rightleftharpoons {\text{PCl}}_{\text{5}}(g)+\text{heat}$

When stress is applied on a system that is at equilibrium, the system adjusts itself to get relieved from the stress.  As in the given equilibrium reaction, heat energy is liberated, it is an exothermic reaction.  Decrease in temperature shifts the equilibrium to the right.  Therefore, concentration of ${\text{PCl}}_{\text{3}}$ decreases.

(e)

Interpretation Introduction

Interpretation:

Addition of catalyst to the given equilibrium reaction results in increase, decrease, or no change in the amount of ${\text{PCl}}_{\text{3}}$ has to be predicted.

    ${\text{PCl}}_{\text{3}}(g)+{\text{Cl}}_{\text{2}}(g)\rightleftharpoons {\text{PCl}}_{\text{5}}(g)+\text{heat}$

Concept Introduction:

Refer part (a).

Explanation of Solution

Given reaction is,

    ${\text{PCl}}_{\text{3}}(g)+{\text{Cl}}_{\text{2}}(g)\rightleftharpoons {\text{PCl}}_{\text{5}}(g)+\text{heat}$

Addition of catalyst increases both rate of forward reaction and reverse reaction.  Therefore, there is no change in concentration of the reactant or product.  There will not be any shift in the equilibrium also.  Addition of catalyst increases the rate at which the equilibrium can be attained only.  Therefore, there will not be any change in concentration of ${\text{PCl}}_{\text{3}}$.