Equilibrium (2)

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

1. Which are correct statements concerning a chemical reaction in a state of equilibrium?

I. The rate of the forward reaction is equal to the rate of the reverse reaction

II. The concentrations of reactants and products do not change

III. The forward and reverse reactions are still continuing

A. I and II only

B. I and III only

C. II and III only

D. I, II and III

2. Which must be a correct statement about the value of the equilibrium constant, K_c, for a reversible reaction which hardly proceeds in the forward direction?

A. K_c = 0

B. K_c = 1

C. K_c >> 1

D. K_c << 1

3. What will be the effect on the value of K_c and the position of equilibrium when the temperature
is decreased in the following reaction?

3H₂(g) + N₂(g) ⇌ 2NH₃(g) ∆H = – 92 kJ

4. What is the correct equilibrium expression for the following reaction?

3A(g) + 2B(g) ⇌ 2C(g) + 3D(g)

2NO₂(g) ⇌ N₂O₄(g) ∆H = – 24 kJ

A. Raising the temperature.

B. Lowering the pressure.

C. Adding a catalyst.

D. Adding some NO₂(g) to the equilibrium mixture.

6. Which change will not affect the position of equilibrium for the following reaction?

H₂(g) + I₂(g) ⇌ 2HI(g) ∆H = – 10.4 kJ

A. Increasing the temperature by 10 ^oC.

B. Removing some hydrogen iodide from the equilibrium mixture.

C. Doubling the pressure.

D. Adding some iodine to the equilibrium mixture.

7. Which will give an increased yield of sulfur trioxide in the equilibrium reaction for the
Contact Process?

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

I. Adding more oxygen

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. When carbon dioxide dissolves in water the following reaction occurs.

CO₂(g) + H₂O(l) ⇌ H⁺(aq) + HCO₃⁻(aq)

What will happen to the pH of the solution if the carbon dioxide escapes as a gas?

A. It will decrease

B. It will increase

C. It will stay the same

D. It will become negative

9. Which will increase the rate of the following reaction but not affect the value of K_c?

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

A. Decreasing the pressure

B. Using a suitable catalyst

C. Decreasing the temperature

D. Increasing the temperature

10. The equilibrium constant K_c is 160 at 298 K for the following reaction.

H₂(g) + I₂(g) ⇌ 2HI(g)

At 700 K the value for the equilibrium constant is 54. What can be deduced from this information?

A. The position of equilibrium lies on the right at all temperatures.

B. The reaction is exothermic.

C. The rate of the reaction is higher at higher temperatures.

D. Hydrogen iodide will decompose at low temperatures

11. Some water is present at equilibrium in a sealed container at 298 K. What will be the effect of heating the water by 10 K and allowing it to re-establish equilibrium?

A. More of the water will be in the liquid state at the higher temperature.

B. The rate of vaporization will be greater than the rate of condensation for the new equilibrium.

C. At the higher temperature the liquid and the vapour will be in a state of dynamic equilibrium.

D. The rate of condensation will be greater than the rate of vaporization for the new equilibrium.

12. The equilibrium constant for a reaction has the value of 10 at 298 K. Which statement must be true?

A. The forward reaction is spontaneous at 298 K.

B. The enthalpy change for the reaction, ΔH, must be negative.

C. The entropy change for the reaction, ΔS, must be positive.

D. The free energy change, ΔG, must be positive.

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

H₂(g) + I₂(g) ⇌ 2HI(g) ∆H = – 10.4 kJ
What will be the value of the equilibrium constant for the reverse reaction?

A. K_c

B. K_c^½

C. K_c^-1

D. K_c²

14. Consider the standard electrode potentials for the following two reactions:

Zn²⁺(aq) + 2e^– ⇄ Zn(s) E^⦵ = – 0.76 V

Cu²⁺(aq) + 2e^– ⇄ Cu(s) E^⦵ = + 0.34 V

When a zinc half-cell is connected to a copper half-cell using a salt bridge under standard conditions what will be the voltage produced by the cell when the reaction has reached equilibrium?

A. – 1.10 V

B. 0 V

C. + 0.42 V

D. + 1.10 V

15. Which is a correct statement about a mixture of ethanol liquid and ethanol vapour in
equilibrium at its boiling point?

A. All the ethanol molecules posses the same kinetic energy.

B. There are strong hydrogen bonds between the ethanol molecules in the vapour state.

C. The vapour will be at a higher temperature than the liquid.

D. The vapour pressure of the ethanol is equal to the external pressure.

16. The value of K_c for the following reaction is equal to 4 at 298 K.

C₂H₅OH(l) + CH₃COOH(l) ⇄ CH₃COOC₂H₅(l) + H₂O(l)

The reaction quotient, Q, for a mixture of ethanol, water, ethyl ethanoate and ethanoic acid is equal to 6 at 298 K at time t. Which statement will be true when the mixture reaches equilibrium at 298 K?

A. The concentration of ethanol will have decreased.

B. The concentration of ethanoic acid will have decreased.

C. The concentration of ethyl ethanoate will have decreased.

D. The concentration of water will be unchanged.

17. Carbon monoxide and hydrogen can react together to form methanol.

CO(g) + 2H₂(g) ⇌ CH₃OH(g)

The concentrations of the three components in a particular mixture at equilibrium are [CO] = 0.25 mol dm^-3, [H₂] = 0.20 mol dm^-3 and [CH₃OH] = 10 mol dm^-3. What is the value of the equilibrium constant for the reaction at the temperature the concentrations refer to?

A. 2.0 x 10²

B. 1.0 x 10³

C. 1.0 x 10^-3

D. 5.0 x 10^-3

18. At 700 K, K_c = 3.33 x 10^-5 for the reaction

2SO₃(g) ⇌ 2SO₂(g) + O₂(g)

Which relationship must be true at equilibrium?

A. [SO₂] = [SO₃]

B. 2[SO₂] = [O₂]

C. [SO₃] < [SO₂]

D. [SO₂] < [SO₃]

19. When 3.0 mol of ethanol and 3.0 mol of ethanoic acid are reacted together at 298 K and allowed to reach equilibrium the amount of ethyl ethanoate in the equilibrium mixture is 2.0 mol. What is the value of the equilibrium constant for the following reaction at 298 K?

C₂H₅OH(l) + CH₃COOH(l) ⇌ CH₃COOC₂H₅(l) + H₂O(l)

A. 0.44

B. 1.5

C. 2.25

D. 4.0

20. In a solution of carbonic acid two acid dissociation reactions take place.

H₂CO₃(g) ⇌ HCO₃⁻(aq) + H⁺(aq)

HCO₃⁻(g) ⇌ CO₃²⁻(aq) + H⁺(aq)

The pK_a value for the first dissociation of carbonic acid to give the hydrogencarbonate ion is 6.38. Which species will be present in the highest concentration in a 0.01 mol dm^-3 solution of carbonic acid at equilibrium?

A. H₂CO₃

B. HCO₃⁻

C. H⁺

D. CO₃²⁻

Answers

Download the Equilibrium Topics 7 & 17 MC (2) test

Download the answer grid with the correct answers to cut out for Topics 7 & 17 MC (2) Answers