Equilibrium Practice Test # 2

1. The slowest of the following reactions is:

A. Ag⁺_(aq) + Cl^-_(aq) → AgCl_(s)

B. H⁺_(aq)+ OH^-_(aq)→ 2H₂O_(l)

C. 3Ba²⁺_(aq) + 2PO₄^3-_(aq)→ Ba₃(PO₄)_2(aq)

D. Cu_(s) + 2Ag⁺_(aq) → Cu²⁺_(aq)+ 2Ag_(s)

2. The rate of a chemical reaction is equal to the slope of the line with axes labelled

x-axis y-axis

A. time rate

B. mass time

C. volume of gas time

D. time concentration

3. Consider the following reaction: CH_4(g) + 2O_2(g) → CO_2(g) + 2H₂O_(g) + heat

The diagram that represents the relationship between rate and temperature is:

4. Which of the following describes the energy of colliding particles as reacting molecules approach each other?

KE PE

A. decreases increases

B. increases decreases

C. decreases remains constant

D. remains constant increases

5. The average kinetic energy per molecule can be increased by

A. adding a catalyst

B. increasing pressure

C. increasing temperature

D. increasing reactant concentration

6. Consider the following reaction: C_(s) + 2H_2(g)⇄ CH_4(g) ΔH = -74.8 kJ

Which of the following will cause an increase in the value of the Keq?

A. increasing [H₂]

B. decreasing the volume

C. finely powdering the C_(s)

D. decreasing the temperature

7. Consider the following equilibrium: H_2(g) + I_2(g) ⇄ 2HI_(g)

At equilibrium [H₂] = 0.00220 M, [I₂] = 0.00220 M, and [HI] = 0.0156 M

The value of the Keq is

A. 3.10 x 10^-4

B. 1.99 x 10^-2

C. 5.03 x 10¹

D. 3.22 x 10³

8. Consider the rate diagram for the following reaction: 2HI_(g) ⇄ H_2(g) + I_2(g)

Which of the following occurs at t₁?

A. addition of H₂

B. addition of HI

C. addition of a catalyst

D. a decrease in volume

9. Chemical equilibrium is said to be dynamic because

A. the reaction proceeds quickly

B. the mass of the reactants is decreasing

C. the macroscopic properties are constant

D. both forward and reverse rates are occurring

10. Which equation has the largest value of Keq?

A. N_2(g) + O_2(g)⇄ 2NO_(g) ΔH = 21 kJ

B. C₂H_6(g) ⇄ 2C_(s) + 3H_2(g) ΔH + 83 kJ

C. H_2(g) + 1/2O_2(g) ⇄ H₂O_(g) ΔH = -240 kJ

D. Ca_(s) + 3H₂O_(l) ⇄ Ca(OH)_2(aq) + H_2(g) ΔH = -240 kJ

11. The value of the Keq can be changed by

A. adding a catalyst

B. changing the temperature

C. changing the reactant concentration

D. changing the volume of the container

12. Consider the following equilibrium: PCl_3(g) + Cl_2(g) ⇄ PCl_5(g)

When 0.40 mole of PCl₃ and 0.40 mole of Cl₂ are placed in a 1.00 L container and allowed to reach equilibrium, 0.244 mole of PCl₅ are present. From this information, the value of the Keq is

A, 0.10

B. 0.30

C. 3.3

D. 10

13. Consider the following equilibrium: PCl_3(g) + Cl_2(g) ⇄ PCl_5(g) Keq = 2.30

A 1.0 L container is filled with 0.05 mole PCl₅, 1.0 mole PCl₃, and 1.0 mole Cl₂. The system proceeds to the

A. left because the Trial Keq > Keq

B. left because the Trial Keq < Keq

C. right because the Trial Keq > Keq

D. right because the Trial Keq < Keq

14. Given the following system: 2CrO₄^2-_(aq) + 2H⁺_(aq) ⇄ Cr₂O₇^2-_(aq) + H₂O_(l)

Which of the following chemicals, when added to the above system at equilibrium, would result in a decrease in [Cr₂O₇^2-]?

A. NaOH

B. HNO₃

C. Na₂CrO₄

D. Na₂Cr₂O₇

15. What is the Keq expression for the following equilibrium?

3Fe_(s)+ 4H₂O_(g) ⇄ Fe₃O_4(s) + 4H_2(g)

A. Keq = [H₂]⁴

B. Keq = [H₂]

[H₂O]

C. Keq = [H₂]⁴

[H₂O]⁴

D. Keq = [Fe₂O₃][H₂]⁴

[Fe][H₂O]⁴

16. Consider the following equilibrium: 2O_3(g) ⇄ 3O_2(g) Keq = 65

Initially 0.10 mole of O₃ and 0.10 mole of O₂ are placed in a 1.0 L container, Which of the following describes the changes in concentrations as the reaction proceeds towards equilibrium?

[O₃] [O₂]

A. decreases decreases

B. decreases increases

C. increases decreases

D. increases increases

17. Consider the following equilibrium: 2CrO₄^2-_(aq) + 2H⁺_(aq) ⇄ Cr₂O₇^2-_(aq) + H₂O_(l)

yellow orange

An unknown solution is added to an orange equilibrium system until the sample turns yellow. The solution could be

A. KNO₃

B. NaOH

C. NH₄NO₃

D. CH₃COOH

18. Consider the following equilibrium:

CH₃COOH_(aq) ⇄ CH₃COO^-_(aq) + H⁺_(aq) + heat

A stress was applied at time t₁ and the data plotted on the following graph:

The stress imposed at time t₁ is the result of

A. the addition of HCl

B. decreasing the temperature

C. the addition of NaCH₃COO

D. increasing the volume of the container

19. Consider the following potential energy diagram for an equilibrium system:

When the temperature of the system is increased, the equilibrium shifts to the

A. left and the Keq increases

B. left and the Keq decreases

C. right and the Keq increases

D. right and the Keq decreases

20. Addition of a catalyst to an equilibrium system

A. increases the value of the Keq

B. increases the yield of the product

C. has no effect on the rates of the reaction

D. increases the rates of formation of both reactants and products

21. Ammonia, NH₃, is produced by the following reaction:

N_2(g) + 3H_2(g) D 2NH_3(g) + energy

Which of the following would result in the highest concentration of ammonia at equilibrium?

A. increasing the temperature and increasing the pressure

B. decreasing the temperature and increasing the pressure

C. increasing the temperature and decreasing the pressure

D. decreasing the temperature and decreasing the pressure

22. Consider the following equilibrium:

2NO_2(g)D N₂O_4(g)K_eq = 1.15

The equilibrium concentration of NO₂ is 0.05 mol/L. Calculate the equilibrium concentration of N₂O_4(g).

A. 0.22 mol/L

B. 0.29 mol/L

C. 0.43 mol/L

D. 0.58 mol/L

23. Consider the following equilibrium:

H_2(g) + I₂ D 2HI_(g) K_eq= 50.0

What is the value K_eq for the reaction rewritten as:

2HI_(g)D H_2(g)+ I_2(g) K_eq= ?

A. -50.0

B. 0.0200

C. 25.0

D. 50.0

24. Consider the following equilibrium: 2NOCl_(g) D 2NO_(g) + Cl_2(g)

A flask is filled with NOCl, NO, and Cl_2(g). Initially there were a total of 5.0 moles of gases present. When equilibrium is reached, there are a total of 8.0 moles of gases present. Which of the following explains the observation?

A. The reaction shifted left because the Trial Keq > Keq

B. The reaction shifted left because the Trial Keq < Keq

C. The reaction shifted right because the Trial Keq > Keq

D. The reaction shifted right because the Trial Keq < Keq

25. Consider the following equilibrium:

4NH_3(g)+ 5O_2(g) D 4NO_(g) + 6H₂O_(g) + energy

Which of the following will cause the equilibrium to shift to the left?

A. adding H₂O_(g)

B. removing some NO_(g)

C. increasing the volume

D. decreasing the temperature

26. A catalyst is added to a system already at equilibrium. How are the forward and reverse reaction rates affected by the addition of the catalyst.

Forward Rate Reverse Rate

A. increases increases

B. increases constant

C. constant decreases

D. constant constant

27. Consider the following equilibrium: 2NOBr_(g) D 2NO_(g) + Br_2(g) Keq = 0.064

At equilibrium, a 1.00 L flask contains 0.030 mole NOBr and 0.030 mole NO. How many moles of Br₂ are present?

A. 0.0019

B. 0.064

C. 0.030

D. 0.47

28. Which of the following does not apply to all chemical equilibrium systems?

A. They are closed.

B. The macroscopic properties are constant

C. Forward and reverse rates are equal

D. There are equal concentrations of reactants and products

29. The relationship between Ea and reaction rate is best represented as

30. The relationship between Keq and temperature for an exothermic reaction is best represented as

31. The relationship between reaction rate and temperature is best represented by

32. The relationship between Ea and temperature is best represented by

32. Methanol, CH₃OH, can be produced by the following:

CO_(g) + 2H_2(g) D CH₃OH_(g) + energy

The conditions necessary to maximize the equilibrium yield of CH₃OH are

A. low temperature and low pressure

B. high temperature and low pressure

C. low temperature and high pressure

D. high temperature and high pressure

33. Consider the following equilibrium: 2NO_(g) + O_2(g) D 2NO_2(g) + energy

When the volume of the container is increased, the equilibrium shifts to the

A. left and the Keq decreases

B. right and the Keq increases

C. left and the Keq remains constant

D. right and the Keq remains comstant

34. Consider the following reaction:

C₃H_8(g)+ 5O_2(g) Š 3CO_2(g) + 4H₂O_(g)@H = -2202 kJ

Which of the following applies to the forward reaction?

Entropy Enthalpy

A. increases increases

B. increases decreases

C. decreases increases

D. decreases decreases

Subjective

1. Consider the following equilibrium:

N₂H_4(g)+ 2O_2(g) D 2NO_2(g) + 2H₂O_(g)

More oxygen is added to the above equilibrium. After the system re-establishes equilibrium, identify the substance(s), if any, that have a net

a) increase in concentration NO H₂O O₂

b) decrease in concentration N₂H₄

2. Given the following equilibrium: H_2(g) + I_2(g) D 2HI_(g)

Initially, 0.200 mole H₂ and 0.200 mole I₂ were placed into a 1.0 L container. At equilibrium, the [I₂] is 0.040 M. Calculate the Keq.

H_2(g) + I_2(g) D 2HI_(g)

I 0.200 M 0.200 M 0

C 0.160 M 0.160 M 0.320 M

E 0.040 M 0.040 M 0.320 M

Keq = (0.320)² = 64

(040)²

3. Consider the following equilibrium: 2CrO₄^2-_(aq) + 2H⁺_(aq) ⇄ Cr₂O₇^2-_(aq) + H₂O_(l)

yellow orange

When HCl is added, the solution turns orange. Explain why this colour change occurs.

Adding HCl increases the [H⁺] and shifts the system right turning orange.

4. Consider the following equilibrium system:

N_2(g) + 3H_2(g) D 2NH_3(g) + energy

A 1.00 L container is filled with 7.0 mole NH₃ and the system proceeds to equilibrium as indicated by the graph.

a) Draw and label the graph for N₂ and H₂. Fill in an ICE chart if you are not sure how to do this.

N_2(g) + 3H_2(g) D 2NH_3(g)

I 0 0 7.0

C 3.0 9.0 6.0

E 3.0 9.0 1.0

b) Calculate the Keq for the above reaction.

Keq = (1.0)² = 0.00046

(3.0)(9.0)³

5. Consider the following equilibrium 2NO_(g) + O_2(g) D 2NO_2(g) Keq = 1.5

0.800 mole NO, 0.600 moles O₂, and 0.400 moles NO₂ are placed in a vessel that 2.0 L. Show by calculation that the reaction is not at equilibrium? What will happen to [O₂] as equilibrium is approached?

Trial Keq = (0.200)² = 0.833 < Keq = 1.5

(0.400)²(0.300)

Not at equilibrium Shifts Right [O₂] will decrease.

6. Consider the following equilibrium:

SO_3(g)+ NO_(g) D NO_2(g) + SO_2(g) Keq = 0.500

Exactly 0.100 mole SO₃ and 0.100 mole NO were placed in a 1.00 L flask and allowed to go to equilibrium. Calculate the equilibrium concentration of SO₂.

SO_3(g)+ NO_(g) D NO_2(g) + SO_2(g)

I 0.100 0.100 0 0

C x x x x

E 0.100 – x 0.100 – x x x

x² = 0.500

(0.100 – x)²

x = 0.7071

0.100 – x

1.7071x = 0.07071

x = 0.0414 M

[SO₂] = 0.0414 M