# Equilibria and Equilibrium Constants (Worksheet)

Name: ______________________________

Section: _____________________________

Student ID#:__________________________

Work in groups on these problems. You should try to answer the questions without accessing the Internet.

## Q8.1

On the line, write the letter of the description that best matches each term. Each letter can be used once, more than once, or not at all.

• Equilibrium position _______
• Law of chemical equilibrium _______
• Reaction quotient _______
• Law of mass action _______
• Equilibrium constant _______

Characteristics

1. used to determine if a reaction has reached equilibrium
2. depends on the initial concentrations of the substances in a reaction
3. states that every reaction proceeds to an equilibrium state with a specific $$K_{eq}$$
4. expresses the relative concentration of reactants and products at equilibrium in terms of an equilibrium constant
5. the ratio of product concentration to reactant concentration at equilibrium

## Q8.2

What is the equilibrium expression for the equation $$H_2(g) + I_2(g) \rightleftharpoons 2HI(g)$$?

## Q8.3

What is the equilibrium expression for the equation $$NH_4Cl(s) \rightleftharpoons NH_3(g) + HCl(g)$$?

## Q8.4

What is the equilibrium expression for the equation $$As_4O_6(s) + 6C(s) \rightleftharpoons As_4(g) + 6CO(g)$$?

## Q8.5

$$K_{eq}$$ is $$7.7 \times 10^{-15}$$ for the reaction $$2CO(g) \rightleftharpoons C(s) + CO_2(g)$$. At a particular time, the following concentrations are measured:

• $$[CO]=0.034\, M$$
• $$[CO_2] =3.6 \times 10^{-17} M$$

Is this reaction at equilibrium? If not, which direction will the reaction proceed?

## Q8.6

$$K_{eq}$$ is $$0.2$$ for the reaction $$N_2O_4(g) \rightleftharpoons 2NO_2(g)$$ At a particular time, the following concentrations are measured:

• $$[N_2O_4]=2.0\, M$$
• $$[NO_2] = 0.2\, M$$

Is this reaction at equilibrium? If not, which direction will the reaction proceed?

## Q8.7

On the line, write the letter of the description that best matches each term. Each letter can be used once, more than once, or not at all.

• The equilibrium concentration of products is much greater than that of reactants: _______
• The equilibrium concentration of products is much less than that of reactants: _______
• There is a considerable amount of both reactants and products at equilibrium: _______

Characteristics

1. $$K_{eq}$$ is much greater than 1
2. $$K_{eq}$$ is about equal to 1
3. $$K_{eq}$$ is much less than 1.

## Q8.8

Complete the following charts by writing left, right or none for equilibrium shift, and decreases, increases or remains the same for the concentrations of reactants and products and for the value of $$K_{eq}$$. Remember that pure solids and liquids do not affect equilibrium values.

$N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$

with $$\Delta H = -92 \,kJ/mole\, kcal$$

Stress Equilibrium Shift $$[N_2]$$ $$[H_2]$$ $$[NH_3]$$ $$K_{eq}$$ $$\Delta G_{rxn}$$
Add $$N_2$$ right ---- decreases increases remains the same more negative
Add $$H_2$$ ----
Add $$HN_3$$ ----
Remove $$N_2$$ ----
Remove $$H_2$$ ----
Remove $$HN_3$$ ----
Increase Temperature of Reaction
Decrease Temperature of Reaction
Increase Pressure
Decreased Pressure
• Is this reaction entropically driven as written?
• Is this reaction enthalpically driven as written?
• Under what conditions is this reaction non-spontaneous (if ever)?

## Q8.9

Complete the following charts by writing left, right or none for equilibrium shift, and decreases, increases or remains the same for the concentrations of reactants and products and for the value of $$K_{eq}$$. Remember that pure solids and liquids do not affect equilibrium values.

$NaOH(s) \rightleftharpoons Na^+(aq) + OH^-(aq)$

with $$\Delta H = -10.6\, kcal$$

Stress Equilibrium Shift $$NaOH(s)$$ $$[Na^+]$$ $$[OH^-]$$ $$K_{eq}$$ $$\Delta G_{rxn}$$
Add $$NaOH(s)$$ ----
Add $$NaCl$$, which increases $$Na^+(aq)$$ ----
Add $$KOH$$, which increases $$OH^-(aq)$$ ----
Add $$H^+$$, which decreases $$OH^-(aq)$$ ----
Increase Temperature of Reaction
Decrease Temperature of Reaction
Increase Pressure
Decreased Pressure
• Is this reaction entropically driven as written?
• Is this reaction enthalpically driven as written?
• Under what conditions is this reaction non-spontaneous (if ever)?