Chapter 15 Equilibria How Far Do Reactions Go? Exam Prep

Chapter 15: Equilibria: how far do reactions go?

Test Bank

Type: multiple choice question

Title: Chapter 15 - Question 01

1) What is the equilibrium constant for the reaction A ⇌ 2B if the equilibrium concentrations are [A] = 4.27 × 10^-2 M, [B] = 1.41 × 10^-2 M?

a. 4.66 × 10^-4

b. 7.32 × 10^-3

c. 4.66 × 10^-3

d. 2.86 × 10^-1

e. 4.66

Type: multiple choice question

Title: Chapter 15 - Question 02

2) Consider the equilibrium reaction N₂ + O₂ ⇌ 2NO. The equilibrium constant for this reaction is represented by which one of the following?

a.

b.

c.

d.

e.

Type: multiple choice question

Title: Chapter 15 - Question 03

3) What is the equilibrium constant for the reaction A + 2B ⇌ 3C if the equilibrium concentrations are [A] = 0.413 M, [B] = 0.414 M, [C] = 0.228 M

a. 6.34 × 10^-2

b. 5.43 × 10^-5

c. 7.67 × 10^-7

d. 8.52 × 10^-1

e. 4.91 × 10^-3

Type: multiple choice question

Title: Chapter 15 - Question 04

4) Consider the reaction N₂ + O₂ ⇌ 2NO. At 1800 °C, this reaction has an equilibrium constant of 1.2 × 10^–4. During the course of the reaction, a sample of the reaction mixture is taken, and the concentrations of each component are found to be as follows: [N₂] = 0.055 mol L^-1, [O₂] = 0.081 mol L^-1, and [NO] = 0.003 mol L^-1. In which direction must the reaction proceed for it to reach equilibrium?

a. The reaction must proceed from right to left.

For this reaction, the reaction quotient is represented as follows:

Therefore, Q > K. We see in section 15.3 how a reaction must proceed from left to right to reach equilibrium, if Q > K.

b. The reaction must proceed from left to right.

For this reaction, the reaction quotient is represented as follows:

Therefore, Q > K. We see in section 15.3 how a reaction must proceed from left to right to reach equilibrium, if Q > K.

c. The reaction is already at equilibrium.

For this reaction, the reaction quotient is represented as follows:

Therefore, Q > K. A reaction is only at equilibrium if Q = K. We see in section 15.3 how a reaction must proceed from left to right to reach equilibrium, if Q > K.

Type: multiple choice question

Title: Chapter 15 - Question 05

5) Consider the reaction 3O₂ ⇌ 2O₃ for which ΔH of the forward reaction is +280 kJ mol^-1. If we increase the temperature when the reaction mixture is at equilibrium, what can we expect to happen?

a. We cannot predict what will happen.

b. The equilibrium reaction will shift to the left.

c. The equilibrium reaction will shift to the right.

d. The reaction mixture will be unaltered by the increase in temperature.

Type: multiple choice question

Title: Chapter 15 - Question 06

6) Chlorine reacts with sulfur dioxide to produce thionyl chloride according to the following equilibrium reaction: SO₂ + Cl₂ ⇌ SO₂Cl₂. The forward reaction is exothermic.

What will be the consequences of adding more Cl₂ to the reaction when the reaction is at equilibrium?

a. The temperature of the reaction mixture will rise.

b. The temperature of the reaction mixture will stay the same.

c. The temperature of the reaction mixture will fall.

Type: multiple response question

Title: Chapter 15 - Question 07

7) In the reaction H₂ + I₂ ⇌ 2HI, the equilibrium constant at 400°C is 500. Which of the following statements are true when the reaction is at equilibrium? Select any that apply.

a. The reaction lies almost completely to the left.

b. The reaction lies almost completely to the right.

c. The Gibbs free energy change for the reaction is positive.

d. Neither the forward nor the back reactions are occurring.

e. The Gibbs free energy change for the reaction is negative.

Type: multiple response question

Title: Chapter 15 - Question 08

8) The equilibrium constant for the equilibrium reaction N₂ + 3H₂ ⇌ 2NH₃ is 70 at 500°C. If 0.56 mol of NH₃, 0.42 mol of N₂ and 0.67 mol H₂ are injected into a flask, how will the reagents behave? Select all responses that apply.

a. The reaction will proceed to the right.

b. The overall concentration of N₂ present will increase.

c. The reaction will proceed to the left.

d. The reaction mixture will stay as it is.

e. The overall concentration of NH₃ present will increase.

Type: multiple choice question

Title: Chapter 15 - Question 09

9) If the reaction N₂O₄ ⇌ 2NO₂ is at equilibrium and more N₂O₄ is fed into the reaction mixture, what will happen?

a. The equilibrium reaction will shift to the left.

b. The concentration of NO₂ in the reaction mixture will have increased once equilibrium is re-established, but the concentration of N₂O₄ will remain the same.

c. The concentration of N₂O₄ in the reaction mixture will increase once equilibrium is re-established, but the concentration of NO₂ will remain the same.

d. Equilibrium will not be perturbed.

e. When equilibrium is re-established both the concentration of N₂O₄ and NO₂ will have increased.

Type: multiple choice question

Title: Chapter 15 - Question 10

10) What is the equilibrium constant for the reaction A + B ⇌ 2C if the equilibrium concentrations are: [A] 0.419 M, [B] 0.329 M, [C] 97.2 mM?

a. 0.123 M

b. 0.685

c. 1.47

d. 68537

e. 0.0685

Type: multiple response question

Title: Chapter 15 - Question 11

11) Consider the following equilibrium reaction:

CH₄ + H₂O ⇌ CO + 3H₂.

At 298 K, K = 9.4 × 10^–1

Which of the following statements in relation to this reaction are true? Select all that apply.

Increasing the concentration of CO and decreasing the concentration of CH₄ will both favour the back reaction: an increase in [CO] will be compensated for by the reaction lying more to the left. By contrast, a decrease in [CH₄] will be compensated for by the reaction lying more to the right.

A value of K of <1 tells us that the reaction is not spontaneous. It also tells us that, at equilibrium, the reactants are favoured, and the reaction lies to the left.

a. Increasing the pressure favours the forward reaction.

b. Increasing the concentration of CO favours the back reaction.

c. Decreasing the concentration of CH₄ favours the back reaction.

d. The reaction is spontaneous.

e. At equilibrium, the reaction lies to the left: the reactants are favoured.

Type: multiple response question

Title: Chapter 15 - Question 12

12) Which of the following statements about equilibrium reactions are true? Select all that apply.

At equilibrium, the concentration of reactants and products doesn’t have to be equal. For example, section 15.2 discussed some examples of equilibrium mixtures where the concentrations of reactants and products are different.

When a reaction is at equilibrium, the value of the equilibrium constant is not larger than the value of the reaction quotient. Instead, both K and Q are both equal (section 15.3).

a. The equilibrium constant for a given reaction differs according to the temperature of the system.

b. The equilibrium constant for a given reaction at a particular temperature is the same, regardless of the concentrations of the components of the reaction mixture when they are first mixed.

c. At equilibrium, the concentration of reactants and products is equal.

d. When a reaction is at equilibrium, the value of the equilibrium constant is larger than the value of the reaction quotient.

e. At equilibrium, the rates of the forward and back reactions are equal.

Type: multiple choice question

Title: Chapter 15 - Question 13

13) A large negative ΔG for a reaction suggests which one of the following?

a. The reaction quotient and the equilibrium constant are equal.

b. The reaction is far from equilibrium.

c. There is a lot more product than reactant present.

d. ΔH for the reaction is large and positive.

Type: multiple response question

Title: Chapter 15 - Question 14

14) Which of the following phrases correctly complete the sentence “When ΔG = 0 for a chemical reaction, …”. Select all that apply.

When a reaction is about to start, the reaction mixture will be composed entirely of reactants (when considered from the point of view of the forward reaction); when ΔG = 0, however, the reaction is at equilibrium – that is, the reaction has already started.

A value of ΔG of 0 does not tell us that a reaction is spontaneous. Instead, the reaction is only spontaneous if ΔG is negative (that is, <0).

a. …the reaction is about to start.

b. …the reaction is at equilibrium.

c. …ΔH is equal to TΔS.

d. …the reaction is spontaneous.

Type: multiple choice question

Title: Chapter 15 - Question 15

15) Consider the equilibrium reaction A + 2B ⇌ 3C. When the reaction mixture is sampled prior to equilibrium being reached, it is determined that the reaction must proceed to the left for equilibrium to be reached. When the reaction mixture is sampled at equilibrium, the following concentrations are measured: [A] 0.267 mol L^-1, [B] 0.336 mol L^-1 , [C] 0.173 mol L^-1. What were the most likely concentrations of A, B, and C when the reaction mixture was sampled prior to equilibrium?

a. [A] = 0.124 mol L^-1; [B] = 0.225 mol L^-1; [C] = 0.334 mol L^-1

b. [A] = 0.334 mol L^-1; [B] = 0.225 mol L^-1; [C] = 0.124 mol L^-1

c. [A] = 0.225 mol L^-1; [B] = 0.334 mol L^-1; [C] = 0.124 mol L^-1

Type: true-false

Title: Chapter 15 - Question 16

16) The binding of a potential substrate to an enzyme has a large dissociation constant, K_d. Therefore the enzyme and substrate show a strong affinity for each other. True or false?

a. True

b. False

Type: multiple choice question

Title: Chapter 15 - Question 17

17) Nitrogen and oxygen react together according to the following equilibrium reaction:

N₂(g) + O₂(g) ⇌ 2 NO(g)

If the equilibrium constant for this reaction, K_p, is 2 × 10^-37 at a given temperature what is the partial pressure of NO at equilibrium?

a. 2.7 × 10^-22 kPa

b. 90.9 × 10¹⁸ kPa

c. 1.8 × 10^-17 kPa

d. 3.3 × 10^-34 kPa