Chapter 14

Question 1

Dynamic Equilibrium

Answer 1

• Dynamic Equilibrium for a chemical reaction is the condition in which the rate of the forward reaction equals the rate of the reverse reaction.
• Note: the concentration of reactants and products are not equal at equilibrium.

Question 2

Equilibrium Constant (k)

Answer 2

k = [C]^c[D]^d / [A]^a[B]^b

The ratio (at equilibrium) of the concentrations of the products raised to their stoichiometric coefficients divided by the concentrations of the reactants raised to their stoichiometric coefficients.

Question 3

Law of Mass Action

Answer 3

The relationship between the balanced chemical equation and the expression of the equilibrium constant.

Question 4

Significance of the Equilibrium Constant

Answer 4

• K << 1 Reverse reaction is favored; forward reaction does not proceed very far.
• K ≈ 1 Neither direction is favored; forward reaction proceeds about halfway
• K >> 1 Forward reaction is favored; forward reaction proceeds essentially to completion.

Question 5

Relationship between the Equilibrium Constant and the Chemical Equation

Answer 5

1. If you reverse the equation, invert the equilibrium constant.
2. If you multiply the coefficients in the equation by a factor, raise the equilibrium constant to the same factor.
3. If you add two or more individual chemical equations to obtain an overall equation, multiply the corresponding equilibrium constants by each other to obtain the overall equilibrium constant.

Question 6

Reaction Quotient, Q(c)

Answer 6

• A measure of the progress of a reaction towards equilibrium.
• The ratio at any point in the reaction of the concentrations of the products raised to their stoichiometric coefficients divided by the concentrations of the reactants raised to their stoichiometric coefficients.

Question 7

Direction of Change Predictions (Q vs. K)

Answer 7

• Q < K Reaction goes to the right (towards products)
• Q > K Reaction goes to the left (towards reactants)
• Q = K Reaction is at equilibrium

Question 8

Le Châtelier’s Principle

Answer 8

When a chemical system at equilibrium is disturbed, the system shifts in a direction that minimizes the disturbance.

Question 9

Effect of a Concentration Change on Equilibrium

Answer 9

1. Increasing the concentration of one or more of the reactants (which makes Q < K) causes the reaction to shift to the right (in the direction of the products).
2. Increasing the concentration of one or more of the products (which makes Q > K) causes the reaction to shift to the left (in the direction of the reactants).
3. Decreasing the concentration of one or more of the reactants (which makes Q > K) causes the reaction to shift to the left (in the direction of the reactants).
4. Decreasing the concentration of one or more of the products (which makes Q < K) causes the reaction to shift to the right (in the direction of the products.

Question 10

Effect of Volume Change on Equilibrium

Answer 10

If a chemical system is at equilibrium:

1. Decreasing the volume causes the reaction to shift in the direction that has the fewer moles of gas particles.
2. Increasing the volume causes the reaction to shift in the direction that has the greater number of moles of gas particles.

Question 11

Effect of Temperature Change on Equilibrium

Answer 11

In an exothermic chemical reaction, heat is a product.

1. Increasing the temperature causes an exothermic reaction to shift left (in the direction of the reactants); the value of the equilibrium constant decreases.
2. Decreasing the temperature causes an exothermic reaction to shift right (in the direction of the products); the value of the equilibrium constant increases. In an endothermic chemical reaction, heat is a reactant.
3. Increasing the temperature causes an endothermic reaction to shift right (in the direction of the products); the equilibrium constant increases.
4. Decreasing the temperature causes an endothermic reaction to shift left (in the direction of the reactants); the equilibrium constant decreases.

Question 12

Reverse Reaction

Answer 12

k_reverse = 1/k_forward