Equilibrium

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 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

A. K_c = 0

B. K_c = 1

C. K_c >> 1

D. K_c << 1

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

2NOCl(g) ⇌ 2NO(g) + Cl₂(g)

5. 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

6. 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.

7. 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)

8. 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.

10. 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)

11. 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

12. 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

13. 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.

14. 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

15. 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

16. 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)

17. 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

18. 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 temperture

D. Increasing the temperature

19. 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

20. 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?

Answers

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