Chapter 6, Problem 70P

Consider the exothermic reaction: ${\text{H}}_{{}^{\text{2}}}(g)+{\text{ I}}_{\text{2}}(g)\stackrel{}{\rightleftarrows }\text{ 2 HI}(g)\text{.}$ What effect does each of the following changes have on the direction of equilibrium?
a. decrease $\text{[HI]}$
b. increase ${\text{[H}}_2\text{]}$
c. decrease ${\text{[I}}_2\text{]}$
d. increase temperature
e. decrease temperature
f. Increase pressure

Interpretation Introduction

(a)

Interpretation:

The effect of the decrease in the concentration of HI to the direction of equilibrium should be explained.

Concept Introduction:

The net concentrations of the reactants and products do not change at equilibrium, they are used to define an expression, the equilibrium constant (K) which has a characteristic value

For a reaction at a given temperature,

  $\text{K=}\frac{\left[\text{Products}\right]}{\left[\text{reactants}\right]}$

Le Chatelier's principle is a general rule used to explain the effect of a change in reaction conditions on equilibrium.

Le Chatelier's principle states:

If a chemical system at equilibrium is disturbed, equilibrium will shift in the direction to counteract the change.

Answer to Problem 70P

Equilibrium favor shift to right.

Explanation of Solution

Given information:

  $H_{\text{2}}{\text{(g) + I}}_2(g)\rightleftharpoons \text{2HI(g)}$

  $\begin{array}{l}{H}_{\text{2}}{\text{(g) + I}}_2(g)\rightleftharpoons \text{2HI(g)}\\ \\ \text{K = }\frac{{[HI]}^2}{[H_2][I_2]}\end{array}$

Reactants and products are in equilibrium. With decrease in the HI concentration, equilibrium is disturbed. Then rate of the forward reaction increases.

Equilibrium favors shift to right.

Interpretation Introduction

(b)

Interpretation:

The effect of the increase in the concentration of H₂ to the direction of equilibrium should be explained.

Concept Introduction:

The net concentrations of the reactants and products do not change at equilibrium. They are used to define an expression and the equilibrium constant (K) which has a characteristic value.

For a reaction at a given temperature,

  $\text{K=}\frac{\left[\text{Products}\right]}{\left[\text{reactants}\right]}$

Le Chatelier's principle is a general rule used to explain the effect of a change in reaction conditions on equilibrium.

Le Chatelier's principle states:

If a chemical system at equilibrium is disturbed, equilibrium will shift in the direction to counteract the change.

Answer to Problem 70P

Equilibrium favors shift to right.

Explanation of Solution

Given information:

  $H_{\text{2}}{\text{(g) + I}}_2(g)\rightleftharpoons \text{2HI(g)}$

  $\begin{array}{l}{H}_{\text{2}}{\text{(g) + I}}_2(g)\rightleftharpoons \text{2HI(g)}\\ \\ \text{K = }\frac{{[HI]}^2}{[H_2][I_2]}\end{array}$

Reactants and products are in equilibrium. With an increase in H₂ concentration, equilibrium is disturbed. Then rate of the forward reaction increases.

Equilibrium favors shift to right.

Interpretation Introduction

(c)

Interpretation:

The effect of the decrease in the concentration of I₂ to the direction of equilibrium should be explained.

Concept Introduction:

The net concentrations of the reactants and products do not change at equilibrium. They are used to define an expression and the equilibrium constant (K) which has a characteristic value.

For a reaction at a given temperature,

  $\text{K=}\frac{\left[\text{Products}\right]}{\left[\text{reactants}\right]}$

Le Chatelier's principle is a general rule used to explain the effect of a change in reaction conditions on equilibrium.

Le Chatelier's principle states:

If a chemical system at equilibrium is disturbed, equilibrium will shift in the direction to counteract the change.

Answer to Problem 70P

Equilibrium favors shift to left.

Explanation of Solution

Given information:

  $H_{\text{2}}{\text{(g) + I}}_2(g)\rightleftharpoons \text{2HI(g)}$

  $\begin{array}{l}{H}_{\text{2}}{\text{(g) + I}}_2(g)\rightleftharpoons \text{2HI(g)}\\ \\ \text{K = }\frac{{[HI]}^2}{[H_2][I_2]}\end{array}$

Reactants and products are in equilibrium. With decrease of I₂ concentration, equilibrium is disturbed. Then rate of the reverse reaction increases.

Equilibrium favors shift to the left.

Interpretation Introduction

(d)

Interpretation:

The effect of the increase in temperature to the direction of equilibrium should be explained.

Concept Introduction:

The net concentrations of the reactants and products do not change at equilibrium. They are used to define an expression and the equilibrium constant (K) which has a characteristic value.

For a reaction at a given temperature,

  $\text{K=}\frac{\left[\text{Products}\right]}{\left[\text{reactants}\right]}$

Le Chatelier's principle is a general rule used to explain the effect of a change in reaction conditions on equilibrium.

Le Chatelier's principle states:

If a chemical system at equilibrium is disturbed, equilibrium will shift in the direction to counteract the change.

Answer to Problem 70P

Equilibrium favors shift to left.

Explanation of Solution

Given information:

  $H_{\text{2}}{\text{(g) + I}}_2(g)\rightleftharpoons \text{2HI(g)}$

  $\begin{array}{l}{H}_{\text{2}}{\text{(g) + I}}_2(g)\rightleftharpoons \text{2HI(g)}\\ \\ \text{K = }\frac{{[HI]}^2}{[H_2][I_2]}\end{array}$

Reactants and products are in equilibrium. This is exothermic reaction.

Exothermic reaction release energy to drive the reaction.

  $H_{\text{2}}{\text{(g) + I}}_2(g)\rightleftharpoons \text{2HI(g)}+\text{Temperature }$

With increase of temperature, equilibrium is disturbed. Then rate of the reverse reaction increases.

Equilibrium favor shift to left.

Interpretation Introduction

(e)

Interpretation:

The effect of the decrease in the temperature to the direction of equilibrium should be explained.

Concept Introduction:

The net concentrations of the reactants and products do not change at equilibrium. They are used to define an expression and the equilibrium constant (K) which has a characteristic value.

For a reaction at a given temperature,

  $\text{K=}\frac{\left[\text{Products}\right]}{\left[\text{reactants}\right]}$

Le Chatelier's principle is a general rule used to explain the effect of a change in reaction conditions on equilibrium.

Le Chatelier's principle states:

If a chemical system at equilibrium is disturbed, equilibrium will shift in the direction to counteract the change.

Answer to Problem 70P

Equilibrium favors shift to right.

Explanation of Solution

Given information:

  $H_{\text{2}}{\text{(g) + I}}_2(g)\rightleftharpoons \text{2HI(g)}$

  $\begin{array}{l}{H}_{\text{2}}{\text{(g) + I}}_2(g)\rightleftharpoons \text{2HI(g)}\\ \\ \text{K = }\frac{{[HI]}^2}{[H_2][I_2]}\end{array}$

Reactants and products are in equilibrium. This is exothermic reaction.

Exothermic reaction release energy to drive the reaction.

  $H_{\text{2}}{\text{(g) + I}}_2(g)\rightleftharpoons \text{2HI(g)}+\text{Temperature }$

With decrease of temperature, equilibrium is disturbed.

Equilibrium favor shift to right.

Interpretation Introduction

(f)

Interpretation:

The effect of the increase of pressure to the direction of equilibrium should be explained.

Concept Introduction:

The net concentrations of the reactants and products do not change at equilibrium. They are used to define an expression and the equilibrium constant (K) which has a characteristic value.

For a reaction at a given temperature,

  $\text{K=}\frac{\left[\text{Products}\right]}{\left[\text{reactants}\right]}$

Le Chatelier's principle is a general rule used to explain the effect of a change in reaction conditions on equilibrium.

Le Chatelier's principle states:

If a chemical system at equilibrium is disturbed, equilibrium will shift in the direction to counteract the change.

Answer to Problem 70P

Equilibrium does not change.

Explanation of Solution

Given information:

  $H_{\text{2}}{\text{(g) + I}}_2(g)\rightleftharpoons \text{2HI(g)}$

  $\begin{array}{l}{H}_{\text{2}}{\text{(g) + I}}_2(g)\rightleftharpoons \text{2HI(g)}\\ \\ \text{K = }\frac{{[HI]}^2}{[H_2][I_2]}\end{array}$

Reactants and products are in equilibrium. Both reactant and products are gaseous molecules.

Therefore, with the increase of the pressure the equilibrium will shift towards the side of the reaction with fewer gas molecules.

In here, both sides have the same number of gas molecules. Therefore, equilibrium not changes.

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