Deck 14: Chemical Equilibrium

Question 1

The equilibrium constant for the reaction Ni(s) + 4CO(g) $\rightleftharpoons$ Ni(CO)₄(g) is 5.0 * 10⁴ at 25ºC. What is the equilibrium constant for the reaction Ni(CO)₄(g) $\rightleftharpoons$ Ni(s) + 4CO(g)

A) 2.0 * 10^-5
B) 2.5 * 10⁹
C) 5.0 * 10⁴
D) 5.0 * 10^-4
E) 2.0 * 10^-3

Answer 1

2.0 * 10^-5

Question 2

Which is the correct equilibrium constant expression for the following reaction
Fe₂O₃ (s) + 3H₂ (g) $\rightleftharpoons$ 2Fe (s) + 3H₂O (g)

A) K_c = [Fe₂O₃] [H₂]³ / [Fe]²[H₂O]³
B) K_c = [H₂] / [H₂O]
C) K_c = [H₂O]³ / [H₂]³
D) K_c = [Fe]²[H₂O]³ / [Fe₂O₃] [H₂]³
E) K_c = [Fe] [H₂O] / [Fe₂O₃] [H₂]

Answer 2

K_c = [H₂O]³ / [H₂]³

Question 3

1.25 moles of NOCl were placed in a 2.50 L reaction chamber at 427ºC. After equilibrium was reached, 1.10 moles of NOCl remained. Calculate the equilibrium constant, K_c, for the reaction 2NOCl(g) $\rightleftharpoons$ 2NO(g) + Cl₂(g).

A) 3.0 * 10^-4
B) 1.8 * 10³
C) 1.4 * 10^-3
D) 5.6 * 10^-4
E) 4.1 * 10^-3

Answer 3

5.6 * 10^-4

Question 4

On analysis, an equilibrium mixture for the reaction 2H₂S(g) $\rightleftharpoons$ 2H₂(g) + S₂(g) was found to contain 1.0 mol H₂S, 4.0 mol H₂, and 0.80 mol S₂ in a 4.0 L vessel. Calculate the equilibrium constant, K_c, for this reaction.

A) 1.6
B) 3.2
C) 12.8
D) 0.64
E) 0.8

Question 5

The solubility of silver chloride can be increased by dissolving it in a solution containing ammonia.AgCl (s) $\rightleftharpoons$ Ag⁺ (aq) + Cl^- (aq) K₁ = 1.6 x 10^-10
Ag⁺ (aq) + 2NH₃ (aq) $\rightleftharpoons$ Ag(NH₃)₂⁺ (aq) K₂ = 1.5 x 10⁷
What is the value of the equilibrium constant for the overall reaction
AgCl (s) + 2NH₃ (aq) $\rightleftharpoons$ Ag(NH₃)₂⁺ (aq) + Cl^- (aq) K_net =

A) 1.5 x 10⁷
B) 2.4 x 10^-3
C) 3.1 x 10^-3
D) 2.3 x 10¹⁴
E) 2.4 x 10⁷

Question 6

The equilibrium constant expression for the reaction:
N₂ (g) + O₂ (g) $\rightleftharpoons$ 2NO (g) is

A) K_c = 2[NO]/[N₂][O₂]
B) K_c = [N₂][O₂]/2[NO]
C) K_c = [N₂][O₂]/[NO]²
D) K_c = [NO]²/[N₂][O₂]
E) K_c = [NO]/[N₂][O₂]

Question 7

Carbon tetrachloride reacts at high temperatures with oxygen to produce two toxic gases, phosgene and chlorine.CCl₄(g) + ¹/₂O₂(g) $\rightleftharpoons$ COCl₂(g) + Cl₂(g), K_c = 4.4 * 10⁹ at 1,000 K Calculate K_c for the reaction 2CCl₄(g) + O₂(g) $\rightleftharpoons$ 2COCl₂(g) + 2Cl₂(g).

A) 4.4 * 10⁹
B) 8.8 * 10⁹
C) 1.9 * 10¹⁰
D) 1.9 * 10¹⁹
E) 2.3 * 10^-10

Question 8

Consider the two gaseous equilibria: $\begin{array}{ll}\mathrm{SO}_{2}(\mathrm{g})+~^1/_2 \mathrm{O}_{2}(\mathrm{~g}) \leftrightharpoons \mathrm{SO}_{3}(\mathrm{g}) & \mathrm{K}_{1} \\2 \mathrm{SO}_{3}(\mathrm{g}) \leftrightharpoons \mathrm{SO}_{2}(\mathrm{g})+\mathrm{O}_{2}(\mathrm{g}) & \mathrm{K}_{2}\end{array}$ The values of the equilibrium constants K₁ and K₂ are related by

A) K₂ = K₁²
B) K₂² = K₁
C)K₂ = 1/K₁²
D) K₂ = 1/K₁
E) none of these.

Question 9

The reaction A(g) + 2B(g) $\rightleftharpoons$ C(g) was allowed to come to equilibrium. The initial amounts of reactants placed into a 5.00 L vessel were 1.0 mol A and 1.8 molB. After the reaction reached equilibrium, 1.0 mol of B was found. Calculate K_c for this reaction.

A) 0.060
B) 5.1
C) 17
D) 19
E) 25

Question 10

The brown gas NO₂ and the colorless gas N₂O₄ exist in equilibrium, 2NO₂ $\rightleftharpoons$ N₂O₄. In an experiment, 0.625 mole of N₂O₄ was introduced into a 5.00 L vessel and was allowed to decompose until equilibrium was reached. The concentration of N₂O₄ at equilibrium was 0.0750 M. Calculate K_c for the reaction.

A) 7.5
B) 0.125
C) 0.0750
D) 0.10
E) 0.050

Question 11

A reaction with an equilibrium constant K_c = 1.5 x 10^-25 would consist of which of the following at equilibrium:

A) approximately equal reactants and products
B) some reactants and products with reactants slightly favored
C) some reactants and products with products slightly favored
D) essentially all reactants
E) essentially all products

Question 12

Calculate K_p for the reaction 2NOCl(g) $\rightleftharpoons$ 2NO(g) + Cl₂(g) at 400 ^$\circ$ C if K_c at 400 ^$\circ$ C for this reaction is 2.1 * 10^-2.

A) 2.1 * 10^-2
B) 1.7 * 10^-3
C) 0.70
D) 1.2
E) 3.8 * 10^-4

Question 13

2.50 mol NOCl was placed in a 2.50 L reaction vessel at 400ºC. After equilibrium was established, it was found that 28% of the NOCl had dissociated according to the equation 2NOCl(g) $\rightleftharpoons$ 2NO(g) + Cl₂(g).Calculate the equilibrium constant, K_c, for the reaction.

A) 0.021
B) 0.039
C) 0.169
D) 26
E) 47

Question 14

When the following reaction is at equilibrium, which of these relationships is always true
2NOCl(g) $\rightleftharpoons$ 2NO(g) + Cl₂(g)

A) [NO] [Cl₂] = [NOCl]
B) [NO]² [Cl₂] = [NOCl]²
C) [NOCl] = [NO]
D) 2[NO] = [Cl₂]
E) [NO]² [Cl₂] = K_c[NOCl]²

Question 15

A reaction with an equilibrium constant K_c = 1.5 x 10²¹ would consist of which of the following at equilibrium:

A) approximately equal reactants and products
B) some reactants and products with reactants slightly favored
C) some reactants and products with products slightly favored
D) essentially all reactants
E) essentially all products

Question 16

The equilibrium constant expression for the reaction 2BrF₅ (g) $\rightleftharpoons$ Br₂ (g) + 5F₂ (g) is

A) K_c = [Br₂] [F₂] / [BrF₅]
B) K_c = [Br₂] [F₂]⁵ / [BrF₅]²
C) K_c = [Br₂] [F₂]² / [BrF₅]⁵
D) K_c = [BrF₅]² / [Br₂][F₂]⁵
E) K_c = 2[BrF₅]² / ([Br₂] *5[F₂]⁵)

Question 17

When the following reaction is at equilibrium, which of these relationships is always true
2 O₃(g) $\rightleftharpoons$ 3 O₂(g)

A) [O₃] = [O₂]
B) [O₃]² = [O₂]³
C) K_c[O₃]² = [O₂]³
D) K_c[O₂]³ = [O₃]²
E) K_c[O₂]² = [O₃]³

Question 18

Given the following information: 2A(g) + B(g) $\rightleftharpoons$ A₂B(g) K_p1
2A(g) + C₂(g) $\rightleftharpoons$ 2AC(g) K_p2
3/2A₂(g) + B(g) + C(g) $\rightleftharpoons$ AC(g) + A₂B(g) K_p3
Which relationship represents the equilibrium constant for the reaction:
3A₂(g) + 3B(g) + 2C(g) $\rightleftharpoons$ 3A₂B(g) + C₂(g) K_net = ?

A) K_net = K_p1 x K_p2 x K_p3
B) K_net = K_p1 x 2K_p3 / K_p2
C) K_net = K_p1 - K_p2 + 2 K_p3
D) K_net = K_p1 x K_p3²/ K_p2
E) K_net = K_p1 x K_p2 x K_p3²

Question 19

Given the following information: 2A(g) + B(g) $\rightleftharpoons$ A₂B(g) K_p1
2A(g) + C₂(g) $\rightleftharpoons$ 2AC(g) K_p2
3/2 A₂ + B(g) + C(g) $\rightleftharpoons$ AC(g) + A₂B(g) K_p3
Which relationship represents the equilibrium constant for the reaction:
4A(g) + C₂(g) + A₂B(g) $\rightleftharpoons$ 3A₂(g) + B(g) + 2C(g)

A) K_net = K_p1 x K_p2 x K_p3
B) K_net = K_p1 x K_p2 x 2 K_p3
C) K_net = K_p1 x K_p2 x K_p3²
D) K_net = K_p1 x K_p2/ K_p3
E) K_net = K_p1 x K_p2/ K_p3²

Question 20

The solubility of silver bromide can be increased by dissolving it in a solution containing the thiosulfate anion.
AgBr(s) $\rightleftharpoons$ Ag⁺ (aq) + Br^- (aq) K₁ = 7.7 x 10^-13
Ag⁺(aq) + 2S₂O₃^2- (aq) $\rightleftharpoons$ Ag(S₂O₃)₂^3- (aq) K₂ = 4.7 x 10¹³
What is the value of the equilibrium constant for the overall reaction
AgBr(s) + 2S₂O₃^2-(aq) $\rightleftharpoons$ Ag(S₂O₃)₂^3-(aq) + Br^-(aq)

A) 3.6 x 10^-9
B) 12.4 x 10¹³
C) 4.7 x 10^-9
D) 4.7 x 10¹³
E) 36

Question 21

At 340 K, K_p = 69 for the reaction H₂(g) + I₂(g) (⇌) 2HI(g). 50.0 g of HI is injected into an evacuated 5.00-L rigid cylinder at 340 K. What is the total pressure inside the cylinder when the system comes to equilibrium

A) 2.60 atm
B) 1.76 atm
C) 0.424 atm
D) 2.18 atm
E) 10.9 atm

Question 22

Consider the reaction N₂(g) + O₂(g) $\rightleftharpoons$ 2NO(g), for which K_c = 0.10 at 2,000ºC. Starting with initial concentrations of 0.040 M of N₂ and 0.040 M of O₂, determine the equilibrium concentration of NO.

A) 5.4 * 10^-3 M
B) 0.0096 M
C) 0.013 M
D) 0.080 M
E) 0.10 M

Question 23

For the nitrogen fixation reaction 3H₂(g) + N₂(g) ⇌ 2NH₃(g), K_c = 6.0 * 10^-2 at 500 ^$\circ$ C. If 0.250 M H₂ and 0.050 M NH₃ are present at equilibrium, what is the equilibrium concentration of N₂

A) 0.750 M
B) 2.7 M
C) 0.250 M
D) 0.025 M
E) 1.85 M

Question 24

Hydrogen iodide decomposes according to the equation 2HI(g) $\rightleftharpoons$ H₂(g) + I₂(g), for which K_c = 0.0156 at 400ºC. 0.550 mol HI was injected into a 2.00 L reaction vessel at 400ºC. Calculate the concentration of HI at equilibrium.

A) 0.138 M
B) 0.220 M
C) 0.550 M
D) 0.275 M
E) 0.0275 M

Question 25

Phosgene, COCl₂, a poisonous gas, decomposes according to the equation COCl₂(g) $\rightleftharpoons$ CO(g) + Cl₂(g). Calculate K_p for this reaction if K_c = 0.083 at 900ºC.

A) 0.125
B) 8.0
C) 6.1
D) 0.16
E) 0.083

Question 26

Sodium carbonate, Na₂CO₃(s), can be prepared by heating sodium bicarbonate, NaHCO₃(s) as shown below.2NaHCO₃(s) (⇌) Na₂CO₃(s) + CO₂(g) + H₂O(g) K_p = 0.23 at 100ºC If a sample of NaHCO₃ is placed in an evacuated flask and allowed to achieve equilibrium at 100ºC, what will the total gas pressure be

A) 0.46 atm
B) 0.96 atm
C) 0.23 atm
D) 0.48 atm
E) 0.11 atm

Question 27

Equilibrium is established for the reaction 2X(s) + Y(g) $\rightleftharpoons$ 2Z(g) at 500K, K_c = 100. Determine the concentration of Z in equilibrium with 0.2 mol X and 0.50 M Y at 500K.

A) 3.2 M
B) 3.5 M
C) 4.5 M
D) 7.1 M
E) None of these.

Question 28

K_p for the reaction 4CuO(s) $\rightleftharpoons$ 2Cu₂O(s) + O₂(g) is 0.49 at 1024 ^$\circ$ C. Calculate K_c at this temperature

A) 5.8 x 10^-3
B) 41
C) 52
D) 4.6 x 10^-3
E) 0.49

Question 29

K_p for the reaction of SO₂(g) with O₂ to produce SO₃(g) is 3 * 10²⁴ . Calculate K_c for this equilibrium at 25ºC. (The relevant reaction is 2SO₂(g) + O₂(g) $\rightleftharpoons$ 2SO₃(g).)

A) 3 * 10²⁴
B) 5 * 10²¹
C) 2 * 10²⁰
D) 5 * 10²²
E) 7 * 10²⁵

Question 30

Consider the following reactions and their associated equilibrium constants: $\begin{array}{ll}\mathrm{A}+2 \mathrm{~B} \leftrightharpoons \mathrm{C} & \mathrm{~K}_{1} \\\mathrm{C} \leftrightharpoons \mathrm{D}+\mathrm{E} & \mathrm{~K}_{2}\end{array}$ For the reaction A + 2B (⇌) D + E, having equilibrium constant K_c,

A) K_c = K₁ + K₂
B) K_c = K₁/K₂
C) K_c = K₁ - K₂
D) K_c = (K₁)(K₂)
E) K_c = K₂/K₁

Question 31

At 400ºC, K_c = 64 for the equilibrium H₂(g) + I₂(g) (⇌) 2HI(g). If 3.00 mol H₂ and 3.00 mol I₂ are introduced into an empty 4.0 L vessel, find the equilibrium concentration of HI at 400ºC.

A) 0.15 M
B) 1.2 M
C) 2.4 M
D) 4.8 M
E) 5.8 M

Question 32

15.00 g of solid ammonium hydrogen sulfide is introduced into a 500.-mL flask at 25 ^$\circ$ C, the flask is sealed, and the system is allowed to reach equilibrium. What is the partial pressure of ammonia in this flask if K_p = 0.108 at 25 ^$\circ$ C for NH₄HS(s) ⇌ NH₃(g) + H₂S (g)

A) 0.657 atm
B) 1.25 atm
C) 0.329 atm
D) 14.4 atm
E) 2.50 atm

Question 33

Consider the following equilibria:
2SO₃(g) ⇌ 2SO₂(g) + O₂(g) K_c = 2.3 * 10^-7
2NO₃(g) ⇌ 2NO₂(g) + O₂(g) K_c = 1.4 * 10^-3
Calculate the equilibrium constant for the reaction
SO₂(g) + NO₃(g) ⇌ SO₃(g) + NO₂(g)

A) 78
B) 1.3 * 10^-2
C) 1.6 * 10^-4
D) 3.2 * 10^-10
E) 6.1 * 10³

Question 34

Hydrogen iodide decomposes according to the equation 2HI(g) $\rightleftharpoons$ H₂(g) + I₂(g), for which K_c = 0.0156 at 400ºC. 0.550 mol HI was injected into a 2.00 L reaction vessel at 400ºC. Calculate the concentration of H₂ at equilibrium.

A) 0.275 M
B) 0.138 M
C) 0.0275 M
D) 0.0550 M
E) 0.220 M

Question 35

If one starts with pure NO₂(g) at a pressure of 0.500 atm, the total pressure inside the reaction vessel when 2NO₂(g) $\rightleftharpoons$ 2NO(g) + O₂(g) reaches equilibrium is 0.674 atm. Calculate the equilibrium partial pressure of NO₂.

A) 0.152 atm
B) 0.174 atm
C) 0.200 atm
D) 0.326 atm
E) The total pressure cannot be calculated because K_p is not given

Question 36

At 35ºC, the equilibrium constant for the reaction 2NOCl(g) $\rightleftharpoons$ 2NO(g) + Cl₂(g) is K_c = 1.6 * 10^-5. An equilibrium mixture was found to have the following concentrations of Cl₂ and NOCl: [Cl₂] = 1.2 * 10^-2 M; [NOCl] = 2.8 * 10^-1 M. Calculate the concentration of NO(g) at equilibrium.

A) 1.0 * 10^-4 M
B) 1.0 * 10^-2 M
C) 2.8 * 10^-1 M
D) 2.4 * 10^-2 M
E) 1.6 * 10^-3 M

Question 37

Calculate K_c for the reaction 2HI(g) $\rightleftharpoons$ H₂(g) + I₂(g) given that the concentrations of each species at equilibrium are as follows: [HI] = 0.85 mol/L, [I₂] = 0.60 mol/L, [H₂] = 0.27 mol/L.

A) 5.25
B) 0.22
C) 4.5
D) 0.19
E) 1.6 * 10²

Question 38

At 250ºC, the equilibrium constant K_p for the reaction PCl₅(g) $\rightleftharpoons$ PCl₃(g) + Cl₂(g) is 1.80. Sufficient PCl₅ is put into a reaction vessel to give an initial pressure of 2.74 atm at 250ºC. Calculate the pressure of PCl₅ after the system has reached equilibrium.

A) 1.50 atm
B) 1.24 atm
C) 4.24 atm
D) 0.94 atm
E) 1.12 atm

Question 39

For the reaction SO₂(g) + NO₂(g) $\rightleftharpoons$ SO₃(g) + NO(g), the equilibrium constant is 18.0 at 1,200ºC. If 1.0 mole of SO₂ and 2.0 moles of NO₂ are placed in a 20. L container, what concentration of SO₃ will be present at equilibrium

A) 0.48 mol/L
B) 0.11 mol/L
C) 0.95 mol/L
D) 2.22 mol/L
E) 18 mol/L

Question 40

K_p for the reaction CO₂(g) + C(s) $\rightleftharpoons$ 2CO(g) is 1.47 at 727 ^$\circ$ C. Calculate K_c at this temperature.

A) 1.47
B) 121
C) 0.0246
D) 0.0179
E) 87.7

Question 41

The common allotropes of carbon (graphite and diamond) equilibrate as follows: C(gr) ⇌ C(dia) with equilibrium constant K = 0.32. The molar volumes of graphite and diamond are, respectively, 5.30 cm³/mol and 3.42 cm³/mol; $\Delta$ H_f of diamond is 1.90 kJ/mol. This data suggests that the formation of diamond is favored at

A) low temperatures and low pressures
B) high temperatures and low pressures
C) low temperatures and high pressures.
D) high temperatures and high pressures.

Question 42

Concerning the following reaction at equilibrium: 3Fe(s) + 4H₂O(g) ⇌ Fe₃O₄(s) + 4H₂(g), increasing the concentration of the Fe(s) would:

A) Shift the equilibrium to the right
B) Shift the equilibrium to the left
C) Increase the value of the equilibrium constant, K
D) Decrease the value of the equilibrium constant, K
E) Cause no change

Question 43

For the following reaction at equilibrium, which gives a change that will shift the position of equilibrium to favor formation of more products
2NOBr(g) ⇌ 2NO(g) + Br₂(g), $\Delta$ Hº_rxn = 30 kJ/mol

A) Increase the total pressure by decreasing the volume.
B) Add more NO.
C) Remove Br_2.
D) Lower the temperature.
E) Remove NOBr selectively.

Question 44

For the reaction at equilibrium 2SO₃ ⇌ 2SO₂ + O₂ ( $\Delta$ Hº_rxn= 198 kJ/mol), increasing the reaction temperature would:

A) Shift the equilibrium to the right and increase the value of the equilibrium constant K
B) Shift the equilibrium to the left and increase the value of the equilibrium constant K
C) Shift the equilibrium to the right and decrease the value of the equilibrium constant K
D) Shift the equilibrium to the left and decrease the value of the equilibrium constant K
E) Cause no change

Question 45

Which of these situations will result if some CH₄(g) is removed from the reaction CO(g) + 3H₂(g) ⇌ CH₄(g) + H₂O(g) at equilibrium

A) H₂O will be consumed.
B) More CH₄ and H₂O will be produced.
C) K_p will decrease.
D) More CO will be produced.
E) No change will occur.

Question 46

For the reaction at equilibrium: CO(g) + H₂O(g) ⇌ CO₂(g) + H₂(g), increasing the volume of the container would:

A) Shift the equilibrium to the right
B) Shift the equilibrium to the left
C) Increase the value of the equilibrium constant, K
D) Decrease the value of the equilibrium constant, K
E) Cause no change

Question 47

For the reaction PCl₃(g) + Cl₂(g) ⇌ PCl₅(g) at a particular temperature, K_c = 24.3. Suppose a system at that temperature is prepared with [PCl₃] = 0.10 M, [Cl₂] = 0.15 M, and [PCl₅] = 0.60 M. Which of the following is true based on the above

A) Q_c > K_c, the reaction proceeds from left to right to reach equilibrium
B) Q_c > K_c, the reaction proceeds from right to left to reach equilibrium
C) Q_c < K_c, the reaction proceeds from left to right to reach equilibrium
D) Q_c < K_c, the reaction proceeds from right to left to reach equilibrium
E) Q_c = K_c, the reaction is currently at equilibrium

Question 48

Concerning the following reaction at equilibrium: 3Fe(s) + 4H₂O(g) ⇌ Fe₃O₄(s) + 4H₂(g), increasing the volume of the container would:

A) Shift the equilibrium to the right
B) Shift the equilibrium to the left
C) Increase the value of the equilibrium constant, K
D) Decrease the value of the equilibrium constant, K
E) Cause no change

Question 49

For the following reaction at equilibrium in a reaction vessel, which one of these changes would cause the Br₂ concentration to increase
2NOBr(g) ⇌ 2NO(g) + Br₂(g), $\Delta$ Hº_rxn= 30 kJ/mol

A) Lower the temperature.
B) Remove some NO.
C) Remove some NOBr.
D) Compress the gas mixture into a smaller volume.
E) Add a catalyst

Question 50

Consider this reaction at equilibrium: 2SO₂(g) + O₂(g) ⇌ 2SO₃(g), $\Delta$ Hº_rxn = -198 kJ/mol
If the volume of the system is compressed at constant temperature, what change will occur in the position of the equilibrium

A) A shift to produce more SO₂
B) A shift to produce more O₂
C) No change
D) A shift to produce more SO₃

Question 51

For the equilibrium reaction 2SO₂(g) + O₂(g) ⇌ 2SO₃(g), $\Delta$ Hº_rxn = -198 kJ/mol. Which one of these factors would cause the equilibrium constant to increase

A) Decrease the temperature.
B) Add SO₂ gas.
C) Remove O₂ gas.
D) Add a catalyst.
E) None of these.

Question 52

At 700 K, the reaction 2SO₂(g) + O₂(g) ⇌ 2SO₃(g) has the equilibrium constant K_c = 4.3 * 10⁶, and the following concentrations are present: [SO₂] = 0.010 M; [SO₃] = 10. M; [O₂] = 0.010 M. Which of the following is true based on the above

A) Q_c > K_c, the reaction proceeds from left to right to reach equilibrium
B) Q_c > K_c, the reaction proceeds from right to left to reach equilibrium
C) Q_c < K_c, the reaction proceeds from left to right to reach equilibrium
D) Q_c < K_c, the reaction proceeds from right to left to reach equilibrium
E) Q_c = K_c, the reaction is currently at equilibrium

Question 53

For the reaction at equilibrium: 3Fe(s) + 4H₂O(g) ⇌ Fe₃O₄(s) + 4H₂(g), removing some of the product, Fe₃O₄(s), would:

A) Shift the equilibrium to the right
B) Shift the equilibrium to the left
C) Increase the value of the equilibrium constant, K
D) Decrease the value of the equilibrium constant, K
E) Cause no change

Question 54

Consider this gas phase equilibrium system: PCl₅(g) ⇌ PCl₃(g) + Cl₂(g) $\Delta$ Hº_rxn = +87.8 kJ/mol.Which of these statements is false

A) Increasing the system volume shifts the equilibrium to the right.
B) Increasing the temperature shifts the equilibrium to the right.
C) A catalyst speeds up the approach to equilibrium and shifts the position of equilibrium to the right.
D) Decreasing the total pressure of the system shifts the equilibrium to the right.
E) Increasing the temperature causes the equilibrium constant to increase.

Question 55

For the reaction H₂(g) + I₂(g) ⇌ 2HI(g), K_c = 50.2 at 445ºC. If [H₂] = [I₂] = [HI] = 1.75 * 10^-3 M at 445ºC, which of the following is true based on the above

A) Q_c > K_c, the reaction proceeds from left to right to reach equilibrium
B) Q_c > K_c, the reaction proceeds from right to left to reach equilibrium
C) Q_c < K_c, the reaction proceeds from left to right to reach equilibrium
D) Q_c < K_c, the reaction proceeds from right to left to reach equilibrium
E) Q_c = K_c, the reaction is currently at equilibrium

Question 56

The reaction 2SO₃(g) ⇌2SO₂(g) + O₂(g) is endothermic. If the temperature is increased,

A) more SO₃ will be produced.
B) K_c will decrease.
C) no change will occur in K_c .
D) K_c will increase.
E) the pressure will decrease.

Question 57

For the following reaction at equilibrium in a reaction vessel, which change will cause the Br₂ concentration to decrease
2NOBr(g) ⇌ 2NO(g) + Br₂(g), $\Delta$ Hº_rxn= 30 kJ/mol

A) Increase the temperature.
B) Remove some NO.
C) Add more NOBr.
D) Compress the gas mixture into a smaller volume.
E) Add a catalyst

Question 58

For the following reaction at equilibrium, which change will cause the equilibrium to shift to the left
2NOBr(g) ⇌ 2NO(g) + Br₂(g), $\Delta$ Hº_rxn = 30 kJ/mol

A) Increase the container volume.
B) Remove some NO.
C)Remove some Br₂.
D) Add more NOBr.
E) Decrease the temperature.

Question 59

At 700 K, the reaction 2SO₂(g) + O₂(g) ⇌ 2SO₃(g) has the equilibrium constant K_c = 4.3 * 10⁶ , and the following concentrations are present: [SO₂] = 0.10 M; [SO₃] = 10. M; [O₂] = 0.10 M. Which of the following is true based on the above

A) Q_c > K_c, the reaction proceeds from left to right to reach equilibrium
B) Q_c > K_c, the reaction proceeds from right to left to reach equilibrium
C) Q_c < K_c, the reaction proceeds from left to right to reach equilibrium
D) Q_c < K_c, the reaction proceeds from right to left to reach equilibrium
E) Q_c = K_c, the reaction is currently at equilibrium

Question 60

In which of these gas-phase equilibria is the yield of products increased by increasing the total pressure on the reaction mixture

A) CO(g) + H₂O(g) ⇌ CO₂(g) + H₂(g)
B) 2NO(g) + Cl₂(g) ⇌ 2NOCl(g)
C) 2SO₃(g) ⇌ 2SO₂(g) + O₂(g)
D) PCl₅(g) ⇌ PCl₃(g) + Cl₂(g)
E) H₂(g) + I₂(g) ⇌ 2HI(g)

Question 61

25.0 g of HI(g) is injected into a 4.00 L reaction vessel that contains 20.0 g of I₂(g). When the system comes to equilibrium at 400ºC, what will be the total pressure inside the reaction vessel?
2HI(g) ⇌ H₂(g) + I₂(g), K_c = 0.0156 at 400ºC

A) 2.70 atm
B) 13.0 atm
C) 2.43 atm
D) 0.815 atm
E) 3.24 atm

Question 62

Consider the reaction N₂(g) + 3H₂(g) ⇌ 2NH₃(g). When nitrogen is added to the system at equilibrium, the reaction will shift toward the products.

Question 63

When the substances in the equation below are at equilibrium, at pressure P and temperature T, the equilibrium can be shifted to favor the products by CuO(s) + H₂(g) ⇌ H₂O(g) + Cu(s) $\Delta$ Hº_rxn = -2.0 kJ/mol

A) increasing the pressure by means of a moving piston at constant T.
B) increasing the pressure by adding an inert gas such as nitrogen.
C) decreasing the temperature.
D) allowing some gases to escape at constant P and T.
E) adding a catalyst.

Question 64

Which of the following rate laws is consistent with the following mechanism
A(g) + B(g) ⇌ AB(g) fast equilibrium (K_c1)
AB(g) + C(g) $\rarr$ AC(g) + B(g) slow

A) Rate = k[A][B]
B) Rate = kK_c1[A][B][C]
C) Rate = k[AC][B]/[AB][C]
D) Rate = [AB]/[A][B]
E) Rate = K_c1[AC]/[A][C]

Question 65

A solution was prepared such that the initial concentrations of Cu²⁺(aq) and CN^-(aq) were 0.0120 M and 0.0400 M, respectively. These ions react according to the following chemical equation:
Cu²⁺(aq) + 4CN^-(aq)
Kc= 1.0 x 10²⁵ ⇌ Cu(CN)₄^2-(aq)
What will be the concentration of Cu²⁺(aq) at equilibrium

A) 0.0020 M
B) 0.0040 M
C) 0.0060 M
D) 0.0080 M
E) None of the above

Question 66

Consider this reaction at equilibrium at a total pressure P₁: 2SO₂(g) + O₂(g) ⇌ 2SO₃(g)
Suppose the volume of this system is compressed to one-half its initial volume and then equilibrium is reestablished. The new equilibrium total pressure will be

A) twice P₁.
B) three times P₁.
C) 3.5 P₁.
D) less than twice P₁.
E) unchanged.

Question 67

75.0 g of PCl₅(g) is introduced into an evacuated 3.00 L vessel and allowed to reach equilibrium at 250ºC.PCl₅(g) ⇌ PCl₃(g) + Cl₂(g) If K_p = 1.80 for this reaction, what is the total pressure inside the vessel at equilibrium

A) 2.88 atm
B) 2.27 atm
C) 4.54 atm
D) 7.42 atm
E) 9.69 atm

Question 68

50.0 g of N₂O₄ is introduced into an evacuated 2.00 L vessel and allowed to come to equilibrium with its decomposition product, N₂O₄(g) ⇌ 2NO₂(g). For this reaction K_c = 0.133. Once the system has reached equilibrium, 5.00 g of NO₂ is injected into the vessel, and the system is allowed to equilibrate once again. Calculate the mass of NO₂ in the final equilibrium mixture.

A) 17.8 g
B) 12.4 g
C) 14.7 g
D) 19.7 g
E) 15.5 g

Question 69

When the reaction 2H₂S(g) ⇌ 2H₂(g) + S₂(g) is carried out at 1065 ^$\circ$ C, K_p = 0.012. Starting with pure H₂S at 1065 ^$\circ$ , what must the initial pressure of H₂S be if the equilibrated mixture at this temperature is to contain 0.250 atm of H₂(g)

A) 1.06 atm
B) 1.86 atm
C) 0.94 atm
D) 0.90 atm
E) 1.52 atm

Question 70

Consider the reaction N₂(g) + 3H₂(g) ⇌ 2NH₃(g). When nitrogen is removed from the system at equilibrium, the hydrogen (H₂) concentration will increase.

Question 71

A quantity of liquid methanol, CH₃OH, is introduced into a rigid 3.00-L vessel, the vessel is sealed, and the temperature is raised to 500K. At this temperature, the methanol vaporizes and decomposes according to the reaction CH₃OH(g) ⇌ CO(g) + 2 H₂(g), K_c= 6.90*10^-2.If the concentration of H₂ in the equilibrium mixture is 0.426M, what mass of methanol was initially introduced into the vessel

A) 147 g
B) 74.3 g
C) 33.9 g
D) 49.0 g
E) 24.8 g

Question 72

The equilibrium constants for the chemical reaction N₂(g) + O₂(g) ⇌ 2NO(g) are K_P = 1.1 * 10^-3 and 3.6 * 10^-3 at 2,200 K and 2,500 K, respectively.Which one of these statements is true

A)The reaction is exothermic, $\Delta$ Hº < 0.
B) The partial pressure of NO(g) is less at 2,200 K than at 2,500 K.
C) K_P is less than K_c by a factor of (RT).
D) The total pressure at 2,200 K is the same as at 2,500 K.
E) Higher total pressure shifts the equilibrium to the left.

Question 73

75.0 g of PCl₅(g) is introduced into a 3.00 L vessel containing 10.0 g of Cl₂(g), and the system is allowed to reach equilibrium at 250ºC.PCl₅(g) ⇌ PCl₃(g) + Cl₂(g)
If K_p = 1.80 for this reaction, what is the total pressure inside the vessel at equilibrium

A) 6.83 atm
B) 8.85 atm
C) 5.38 atm
D) 3.47 atm
E) 7.42 atm

Question 74

Consider the reaction N₂(g) + 3H₂(g) ⇌ 2NH₃(g). When hydrogen gas is added to this system at equilibrium, the reaction will shift towards reactants.

Question 75

Which of the following rate laws is consistent with the following mechanism
A₂(g) + C(g) ⇌ AC(g) + A(g) fast equilibrium (K_c1)
AC(g) + B₂(g) $\rarr$ AB₂(g) + C(g) slow

A) Rate = k[A₂][C]
B) Rate = k[AB₂][C]/[AC][B₂]
C) Rate = kK_c1[A₂][C][B₂]/[A]
D) Rate = [A][AB₂]/[A₂][B₂]
E) Rate = kK_c1[AC][A]/[A₂][C]

Question 76

A solution was prepared such that the initial concentrations of Cu²⁺(aq) and CN^-(aq) were 0.0120 M and 0.0400 M, respectively. These ions react according to the following chemical equation:
$\mathrm{Cu}^{2+}(a q)+4 \mathrm{CN}^{-}(a q) \rightleftharpoons \mathrm{Cd}(\mathrm{CN})_{4}^{2-}(a q)$

$\mathrm{K}_{\mathrm{c}}=1.0 \times 10^{25}$
What will be the concentration of CN^-(aq) at equilibrium

A) 2.4 * 10^-7 M
B) 4.4 * 10^-7 M
C) 6.4 * 10^-7 M
D) 8.4 * 10^-7 M
E) None of the above

Question 77

Solid ammonium hydrogen sulfide is introduced into a 2.00-L flask, and the flask is sealed. If this solid decomposes according to the equation below
NH₄HS(s) ⇌ NH₃(g) + H₂S(g), K_p = 0.108 at 25 ^$\circ$ C,
What is the minimum mass of ammonium hydrogen sulfide that must be present in the flask initially if equilibrium is to be established at 25 ^$\circ$ C

A) 0.917 g
B) 1.37 g
C) 2.74 g
D) 0.581 g
E) 0.452 g

Question 78

For the reaction 2NOCl(g) ⇌ 2NO(g) + Cl₂(g), K_c = 8.0 at a certain temperature. What concentration of NOCl must be put into an empty 4.00 L reaction vessel in order that the equilibrium concentration of NOCl be 1.00 M

A) 1.26 M
B) 2.25 M
C) 2.50 M
D) 3.52 M
E) 11.0 M

Question 79

50.0 g of N₂O₄ is introduced into an evacuated 2.00 L vessel and allowed to come to equilibrium with its decomposition product, N₂O₄(g) ⇌ 2NO₂(g). For this reaction K_c = 0.133. Once the system has reached equilibrium, 5.00 g of NO₂ is injected into the vessel, and the system is allowed to equilibrate once again. Calculate the mass of N₂O₄ in the final equilibrium mixture.

A) 39.5 g
B) 35.3 g
C) 30.3 g
D) 25.2 g
E) 43.7 g

Question 80

If the reaction 2H₂S(g) ⇌ 2H₂(g) + S₂(g) is carried out at 1065 ^$\circ$ C, K_p = 0.0120. Starting from pure H₂S introduced into an evacuated vessel at 1065 ^$\circ$ C, what will the total pressure in the vessel be at equilibrium if the equilibrated mixture contains 0.300 atm of H₂(g)

A) 1.06 atm
B) 1.36 atm
C) 2.39 atm
D) 4.20 atm
E) 1.51 atm