Equilibrium (1)

For each question choose the answer you consider to be the best.

1. Which statements about an isolated system at equilibrium are always correct?

I. Energy cannot enter or leave the system

II. None of the products can escape

III. The concentrations of the reactants and products are equal

A. I and II only

B. I and III only

C. II and III only

D. I, II and III

2. Which is the correct expression for the equilibrium constant for the following reaction?

2NOCl(g) ⇌ 2NO(g) + Cl₂(g)

3. Which change will increase the amount of sulfur trioxide in the equilibrium mixture?

2SO₂(g) + O₂(g) ⇌ 2SO₃(g) ∆H = – 197 kJ

A. Increasing the temperature.

B. Adding vanadium pentoxide, V₂O₅(s), as a catalyst.

C. Doubling the volume of the container.

D. Increasing the pressure.

4. What will happen to the value of K_c and the position of equilibrium when some acid is added to the following reversible reaction?

2CrO₄²⁻(aq) + 2H⁺(aq) ⇌ Cr₂O₇²⁻(aq) + H₂O(l)

5. The equilibrium constant for a weak acid dissociating into its ions is known as the acid dissociation constant and has the symbol K_a. Which is the weakest acid?

A. butanoic acid (K_a = 1.51 x 10^-5)

B. 2-methylpropanoic acid (K_a = 1.41 x 10^-5)

C. propanoic acid (K_a = 1.37 x 10^-5)

D. ethanoic acid (K_a = 1.74 x 10^-5)

6. Which are correct statements about the following reaction?

SO₂(g) + Cl₂(g) ⇌ SO₂Cl₂(g) ∆H = – 85 kJ

I. Increasing the pressure shifts the position of equilibrium to the right

II. Increasing the temperature shifts the position of equilibrium to the right

III. Increasing the pressure has no affect on the value of the equilibrium constant.

A. I and II only

B. I and III only

C. II and III only

D. I, II and III

7. Which will give an increased yield of ammonia in the equilibrium reaction for the Haber Process?

3H₂(g) + N₂(g) ⇌ 2NH₃(g) ∆H = – 92 kJ

I. Using iron metal with a high surface area as a catalyst

II. Decreasing the temperature

III. Increasing the pressure

A. I and II only

B. I and III only

C. II and III only

D. I, II and III

8. Which of the following equilibria will not be affected if only the pressure is altered?

A. 2SO₂(g) + O₂(g) ⇌ 2SO₃(g)

B. CO(g) + H₂O(g) ⇌ CO₂(g) + H₂(g)

C. PCl₅(g) ⇌ PCl₃(g) + Cl₂(g)

D. C₂H₄(g) + H₂O(g) ⇌ C₂H₅OH(g)

9. One of the steps in the mIB Docs (2) Teamfacture of nitric acid is the oxidation of ammonia according to the following equation.

4NH₃(g) + 5O₂(g) ⇌ 4NO₂(g) + 6H₂O(g) ∆H = – 901 kJ

Which conditions will increase the yield of nitrogen dioxide in the equilibrium mixture?

I. Removing the water vapour

II. Decreasing the temperature

III. Increasing the pressure

A. I and II only

B. I and III only

C. II and III only

D. I, II and III

10. The hydrogen needed to make ammonia can be obtained from natural gas by the following reaction.

CH₄(g) + H₂O(g) ⇌ CO(g) + 3H₂(g) ∆H = + 210 kJ

Which statement is always correct when the reaction is at equilibrium?

11. A sealed flask at 298 K is half full of water. Which is a correct statement after the flask has been heated to 308 K and the equilibrium has re-established?

A. The rate of condensation is greater than the rate of vaporization.

B. The will be more water molecules present in the flask.

C. There will be more water molecules in the vapour phase.

D. The rate of vaporization is greater than the rate of condensation.

12. Which values correspond to the position of equilibrium for a reaction?

13. K_c is the equilibrium constant for the reaction between hydrogen and iodine:

H₂(g) + I₂(g) ⇌ 2HI(g)

What will be the value of the equilibrium constant for the reaction below?

½H₂(g) + ½I₂(g) ⇌ HI(g)

A. K_c

B. K_c^½

C. K_c^-1

D. K_c²

14. Which correctly describes the relationship between the equilibrium constant, K_c, and the Gibbs free energy for a specified reaction?

A. ΔG = RT lnK_c

B. lnK_c = – RT ΔG

C. K_c = – RT ΔG

D. ΔG = – RT lnK_c

15. The value for the equilibrium constant for the reaction

2SO₂(g) + O₂(g) ⇌ 2SO₃(g)

is 4.0 x 10²⁴ at 298K. What would be the value for the equilibrium constant for the following reaction at the same temperature?

2SO₃(g) ⇌ 2SO₂(g) + O₂(g)

A. 2.0 x 10¹²

B. 2.5 x 10^-25

C. 4.0 x 10²⁴

D. 2.0 x 10²⁴

16. Dinitrogen tetroxide dissociates into nitrogen dioxide according to the equation

N₂O₄(g) ⇌ 2NO₂(g)

The value for the equilibrium constant for this reaction at different temperatures is given in the following table.

Which statement for the reaction is correct?

A. N₂O₄(g) decomposes more readily at high temperatures as the reaction is exothermic.

B. N₂O₄(g) decomposes less readily at high temperatures as the reaction is exothermic.

C. N₂O₄(g) decomposes more readily at high temperatures as the reaction is endothermic.

D. N₂O₄(g) decomposes less readily at high temperatures as the reaction is endothermic.

17. Hydrogen sulfide is a weak acid. Consider the following equilibria in a 0.20 mol dm^-3 solution of hydrogen sulfide.

H₂S(aq) ⇌ HS⁻(aq) + H⁺(aq)

HS⁻(aq) ⇌ S²⁻(aq) + H⁺(aq)

Which species will be present in the highest concentration?

A. H₂S

B. HS⁻

C. H⁺

D. S²⁻

18. A voltaic cell was constructed by connecting a zinc half-cell to a copper half-cell.

Zn²⁺(aq) + 2e⁻ ⇌ Zn(s) E = – 0.76 V

Cu²⁺(aq) + 2e⁻ ⇌ Cu(s) E = + 0.34 V

The overall reaction taking place in the cell is:

Zn(s) + Cu²⁺(aq) ⇌ Zn²⁺(aq) + Cu(s)

What will be the potential difference of the cell when it is in a state of equilibrium?

A. 0 V

B. 1.10 V

C. – 1.10 V

D. 0.42 V

19. The equilibrium expression for a particular reaction is

At a fixed temperature the initial concentrations of W, X, Y and Z are all 1.0 mol dm^-3. What happens to the value of K_c, at the same temperature, if all four initial values are halved to 0.50 mol dm^-3?

A. It is halved.

B. It doubles.

C. It is reduced by a factor of four.

D. It remains the same.

20. A 10.0 dm³ reaction vessel initially contained only 2.0 mol of P and 1.0 mol of Q. When equilibrium was reached, at a temperature of 330 K, 0.50 mol of S were present. What is the equilibrium constant for the following reaction at this temperature?

P(g) + Q(g) ⇌ R(g) + S(g)

A. 0.33

B. 0.25

C. 8.0

D. 3.0

Answers

Download the Equilibrium Topics 7 & 17 MC (1) test

Download the answer grid with the correct answers to cut out for Topics 7 & 17 MC (1) Answers