Term 3 MCQ - Equilibrium 1

1. The equilibrium between nitrogen dioxide, NO2, and dinitrogen tetroxide, N2O4, is shown

below.2NO2(g) N2O4(g) Kc = 0.01

What happens when the volume of a mixture at equilibrium is decreased at a constanttemperature?

I. The value of Kc increases

II. More N2O4 is formed

III. The ratio of]ON[

]NO[

42

2 decreases

A. I and II onlyB. I and III onlyC. II and III onlyD. I, II and III

2. Which statement about chemical equilibria implies they are dynamic?A. The position of equilibrium constantly changes.B. The rates of forward and backward reactions change.C. The reactants and products continue to react.D. The concentrations of the reactants and products continue to change.

3. Which is the correct relationship between enthalpy of vaporization, intermolecular forces andboiling point?

Enthalpy ofvaporization

Intermolecularforces

Boiling point

A. small weak highB. small strong lowC. large weak highD. large strong high

4. For the following reaction Kc = 1.0 × 10–5 at 30 °C.

2NOCl(g) 2NO(g) + Cl2(g)

Which relationship is correct at equilibrium at this temperature?A. The concentration of NO equals the concentration of NOCl.B. The concentration of NOCl is double the concentration of Cl2.

C. The concentration of NOCl is much greater than the concentration of Cl2.

D. The concentration of NO is much greater than the concentration of NOCl.

5. The reaction below represents the Haber process for the industrial production of ammonia.

N2(g) + 3H2(g) 2NH3(g) ∆HO = –92 kJ

The optimum conditions of temperature and pressure are chosen as a compromise between thosethat favour a high yield of ammonia and those that favour a fast rate of production. Economicconsiderations are also important.Which statement is correct?A. A higher temperature would ensure higher yield and a faster rate.B. A lower pressure would ensure a higher yield at a lower cost.C. A lower temperature would ensure a higher yield and a faster rate.D. A higher pressure would ensure a higher yield at a higher cost.

Term 3 MCQ - Equilibrium 2

6. Which statement is correct for a crystal of iron(II) sulfate in a state of equilibrium with asaturated solution of iron(II) sulfate?

A. The colour of the solution darkens as the crystal continues to dissolve.B. The concentration of the iron(II) sulfate solution increases as the water evaporates.C. The shape of the iron(II) sulfate crystal does not change.D. The colour of the solution does not change but the shape of the crystal may change.

7. Consider the equilibrium between methanol, CH3OH(l), and methanol vapour, CH3OH(g).

CH3OH(l) CH3OH(g)

What happens to the position of equilibrium and the value of Kc as the temperature decreases?

Position of equilibrium Value of Kc

A. shifts to the left decreasesB. shifts to the left increasesC. shifts to the right decreasesD. shifts to the right increases

8. What is the equilibrium constant expression, Kc, for the following reaction?

N2O4(g) 2NO2(g)

A. Kc =]O[N

][NO

42

2

B. Kc =]O[N

][NO

42

22

C. Kc =2

42

2

]O[N

][NO

D. Kc = [NO2][N2O4]2

9. Consider the endothermic reaction below.5CO(g) + I2O5(g) 5CO2(g) + I2(g)

According to Le Chatelier’s principle, which change would result in an increase in the amountof CO2?

A. Increasing the temperatureB. Decreasing the temperatureC. Increasing the pressureD. Decreasing the pressure

10. 0.50 mol of I2(g) and 0.50 mol of Br2(g) are placed in a closed flask. The following equilibrium

is established.I2(g) + Br2(g) IBr(g)

The equilibrium mixture contains 0.80 mol of IBr(g). What is the value of Kc?

A. 0.64B. 1.3C. 2.6D. 64

Term 3 MCQ - Equilibrium 3

11. What is the effect of an increase of temperature on the yield and the equilibrium constant for thefollowing reaction?

2H2(g) + CO(g) CH3OH(l) ∆HO = –128 kJ

Yield Equilibriumconstant

A. Increases IncreasesB. Increases DecreasesC. Decreases IncreasesD. Decreases Decreases

12. Which statements about a liquid are correct?I. When the temperature of a liquid in a closed container increases, its vapour

pressure increases.II. When the pressure on a liquid increases, its boiling point increases.III. When the pressure on a liquid increases, its vapour pressure increases.

A. I and II onlyB. I and III onlyC. II and III onlyD. I, II and III

13. Consider the following equilibrium reaction.

2SO2(g) + O2(g) 2SO3(g) ∆Ho = –197 kJ

Which change in conditions will increase the amount of SO3 present when equilibrium is

re-established?A. Decreasing the concentration of SO2

B. Increasing the volumeC. Decreasing the temperatureD. Adding a catalyst

14. Consider the following reversible reaction.

Cr2O72–(aq) + H2O(l) 2CrO4

2–(aq) + 2H+(aq)

What will happen to the position of equilibrium and the value of Kc when more H+ ions are

added at constant temperature?

Position of equilibrium Value of Kc

A. shifts to the left decreasesB. shifts to the right increasesC. shifts to the right does not changeD. shifts to the left does not change

15. Consider this equilibrium reaction in a sealed container:H2O(g) H2O(l)

What will be the effect on the equilibrium of increasing the temperature from 20 ºC to 30 ºC?A. More of the water will be in the gaseous state at equilibrium.B. More of the water will be in the liquid state at equilibrium.C. At equilibrium the rate of condensation will be greater than the rate of evaporation.D. At equilibrium the rate of evaporation will be greater than the rate of condensation.

Term 3 MCQ - Equilibrium 4

16. What effect will an increase in temperature have on the Kc value and the position of equilibrium

in the following reaction?N2(g) + 3H2(g) 2NH3(g) ΔH = –92 kJ

Kc Equilibrium position

A. increases shifts to the rightB. decreases shifts to the leftC. increases shifts to the leftD. decreases shifts to the right

17. Which statement is always correct for a chemical reaction at equilibrium?A. The rate of the forward reaction equals the rate of the reverse reaction.B. The amounts of reactants and products are equal.C. The concentration of the reactants and products are constantly changing.D. The forward reaction occurs to a greater extent than the reverse reaction.

18. Which statement is correct for the equilibrium H2O(l) H2O(g) in a closed system at

100 °C?A. All the H2O(l) molecules have been converted to H2O(g).

B. The rate of the forward reaction is greater than the rate of the reverse reaction.C. The rate of the forward reaction is less than the rate of the reverse reaction.D. The pressure remains constant.

19. An increase in temperature increases the amount of chlorine present in the followingequilibrium.

PCl5(s) PCl3(l) + Cl2(g)

What is the best explanation for this?A. The higher temperature increases the rate of the forward reaction only.B. The higher temperature increases the rate of the reverse reaction only.C. The higher temperature increases the rate of both reactions but the forward reaction is

affected more than the reverse.D. The higher temperature increases the rate of both reactions but the reverse reaction is

affected more than the forward.

20. What will happen when at a constant temperature, more iodide ions, I–, are added to theequilibrium below?

I2(s) + I–(aq) I3–(aq)

A. The amount of solid iodine decreases and the equilibrium constant increases.B. The amount of solid iodine decreases and the equilibrium constant remains unchanged.C. The amount of solid iodine increases and the equilibrium constant decreases.D. The amount of solid iodine increases and the equilibrium constant remains unchanged.

21. Which affects the equilibrium vapour pressure of a liquid in a sealed container, assuming thatthere is always some of the liquid present?A. The temperature of the liquidB. The surface area of the liquidC. The volume of the liquidD. The volume of the container

Term 3 MCQ - Equilibrium 5

22. The sequence of diagrams represents the system as time passes for a gas phase reaction in whichreactant X is converted to product Y.

X =

Y =

Diagram 1

t = 7 seconds

Diagram 2

t = 5 minutes

Diagram

t = 10 minutes

Diagram 4

t = 5 days

Time, t

Which statement is correct?A. At t = 5 days the rate of the forward reaction is greater than the rate of the backward

reaction.B. At t = 7 seconds the reaction has reached completion.C. At t = 10 minutes the system has reached a state of equilibrium.D. At t = 5 days the rate of the forward reaction is less than the rate of the backward

reaction.

23. What changes occur when the temperature is increased in the following reaction at equilibrium?

Br2(g) + Cl2(g) 2BrCl(g) ∆Hο = +14 kJ mol–1

Position of equilibrium Value of equilibrium constantA. Shifts towards the reactants DecreasesB. Shifts towards the reactants IncreasesC. Shifts towards the products DecreasesD. Shifts towards the products Increases

24. For the reaction below:H2(g) + I2(g) 2HI(g)

at a certain temperature, the equilibrium concentrations, in mol dm–3, are[H2(g)] = 0.30, [I2(g)] = 0.30, [HI(g)] = 3.0

What is the value of Kc?

A. 1.0×10–2

B. 10C. 33

D. 1.0×102

25. A liquid and its vapour are at equilibrium inside a sealed container. Which change will alter theequilibrium vapour pressure of the liquid in the container?A. Adding more liquidB. Adding more vapourC. Decreasing the volume of the containerD. Decreasing the temperature

Term 3 MCQ - Equilibrium 6

(Total 1 mark)

Ans to MCQ1. C2. C3. D4. C5. D6. D7. A8. B9. A10. D11. D12. A13. C14. D15. A16. B17. A18. D19. C20. B21. A22. C23. D24. D25. D