Name_______________________________
Date:______________
Period:______
Review Unit 8 Test (Chp 15,17): Chemical and Solubility Equilibrium
1.
Describe dynamic chemical equilibrium in terms of concentrations and rates.
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2.
What does the value of K, as K >1 or K < 1 , describe about a reaction at equilibrium?
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3.
The equilibrium-constant expression for the reaction
Ti(s) + 2 Cl2(g)
TiCl4(l)
is given by
(A)
(B)
(C)
(D)
(E)
4.
[Cl2 (g)]–2
Which of the following changes to a reaction system in equilibrium would affect the value of the
equilibrium constant, Keq, for the reaction? (Assume that all other conditions are held constant.)
(A)
(B)
(C)
(D)
(E)
Adding more of the reactants to the system
Adding a catalyst for the reaction to the system
Changing the temperature of the system
Changing the pressure on the system
Removing some of the products from the system
1
HgO(s) + 4 I– + H2O
5.
HgI42– + 2 OH–
∆H < 0
Which of the following changes will increase the concentration of HgI42– in the equilibrium reaction
above?
(A) Increasing the concentration of OH–
(B) Adding 6 M HNO3
(C) Increasing the mass of HgO present
(D) Increasing the temperature
(E) Adding a catalyst
6.
In which of the following systems would the number of moles of the substances present at equilibrium
NOT be shifted by a change in the volume of the system at constant temperature?
(A) CO(g) + NO(g)
CO2(g) + 1/2 N2(g)
(B) N2(g) + 3 H2(g)
2 NH3(g)
(C) N2(g) + 2 O2(g)
2 NO2(g)
(D)
2 NO2(g)
N2O4(g)
(E) NO(g) + O3(g)
NO2(g) + O2(g)
PCl3(g) + Cl2(g)
7.
PCl5(g) + energy
Some PCl3 and Cl2 are mixed in a container at 200°C and the system reaches equilibrium according
to the equation above. Which of the following causes an increase in the number of moles of PCl5
present at equilibrium?
I. Decreasing the volume of the container
II. Raising the temperature
III. Adding a mole of He gas at constant volume
(A) I only
(B) II only
(C) I and III only
(D) II and III only
(E) I, II, and III
2
2 SO3(g)
8.
2 SO2(g) + O2(g)
When 0.70 mole of SO3 and 0.80 mole of SO2 are placed in an evacuated 1.00-liter flask, the
reaction represented above occurs. After the reactants and the product reach equilibrium and the
initial temperature is restored, the flask is found to contain 0.20 mole of SO3 . Based on these
results, the expression for the equilibrium constant, Kc , of the reaction is _________.
I2(g) + Br2(g)
9.
2 IBr(g)
A sealed 1.0 L flask is charged with 0.35 mol of I2 and 0.35 mol of Br2 .
An equilibrium reaction ensues. When the container contents achieve equilibrium, the flask
contains 0.50 mol of IBr . The value of Keq is __________.
H2(g) + Br2(g)
2 HBr(g)
10. At a certain temperature, the value of the equilibrium constant, K, for the reaction represented above is
2.0 x 105. What is the value of K for the reverse reaction at the same temperature?
(A)
(B)
(C)
(D)
(E)
–2.0 x 10–5
5.0 x 10–6
2.0 x 10–5
5.0 x 10–5
5.0 x 10–4
3
Questions 11-12 refer to the following.
PCl5(g)
PCl3(g) + Cl2(g)
PCl5(g) decomposes into PCl3(g) and Cl2(g) according to the equation above. A pure sample of PCl5(g) is
placed into a rigid, evacuated 1.00 L container. The initial pressure of the PCl5(g) is 1.00 atm.
The temperature is held constant until the PCl5(g) reaches equilibrium with its decomposition products.
The figures below show the initial and equilibrium conditions of the system.
PCl5
Ptotal = 1.00 atm
Figure 1: Initial
11.
Figure 2: Equilibrium
As the reaction progresses toward equilibrium, the rate of the forward reaction
(A)
(B)
(C)
(D)
12.
PCl5 , PCl3 , and Cl2
Ptotal = 1.40 atm
increases until it becomes the same as the reverse reaction rate at equilibrium.
stays constant before and after equilibrium is reached.
decreases to become a constant nonzero rate at equilibrium.
decreases to become zero at equilibrium.
Which of the following statements about Kp , the equilibrium constant for the reaction, is correct?
(A) Kp > 1
(B) Kp < 1
(C) Kp = 1
(D) It cannot be determined whether Kp > 1 , Kp < 1 , or Kp = 1 without additional information.
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13. How is the reaction quotient (Q) of a reaction related to the equilibrium constant (Keq) of the reaction?
(A) Q does not depend on the concentrations or partial pressures of reaction components.
(B) Q is the same as Keq when a reaction is at equilibrium.
(C) When Q < K, the reaction will proceed to the left.
(D) Keq does not change with temperature, whereas Q is temperature dependent.
(E) K does not depend on the concentrations or partial pressures of reaction components.
2 HF(g)
H2(g) + F2(g)
o
14. At 25 C, 10.0 mol of HF(g) are combined with 1.0 moles each of H2(g) and F2(g) in a 1.0 L rigid
container. The value of Kc at 25oC is 0.010. Which of the following will result as the reaction occurs?
(A)
More H2(g) and F2(g) will form.
(B)
More HF(g) will form.
(C)
The total pressure will increase.
(D)
The total pressure will remain constant.
___15. Which of the following compounds would be more soluble in a nitric acid solution than in water?
(A)
(B)
(C)
(D)
(E)
HCl
Ba(OH)2
Al(OH)3
HF
KNO3
___16. Barium sulfate is LEAST soluble in a 0.01-molar solution of which of the following?
(A)
(B)
(C)
(D)
(E)
Al2(SO4)3
(NH4)2SO4
Na2SO4
NH3
BaCl2
___17. In which of the following aqueous solutions would you expect PbI2 to have the greatest solubility?
(A) pure water
(B) 0.020 M BaI2
(C) 0.020 M Pb(NO3)2
(D) 0.030 M NaI
(E) 0.020 M KI
5
___18. What is the molar solubility in water of Ag2CrO4? (The Ksp for Ag2CrO4 is 8 x 10–12)
(A)
(B)
(C)
(D)
(E)
8 x 10–12
2 x 10–12
(4 x 10–12)1/2
(4 x 10–12)1/3
(2 x 10–12)1/3
___19. The solubility of MnCO3 is 5 x 10–10 M . What is the solubility product constant, Ksp, for MnCO3?
(A)
(B)
(C)
(D)
(E)
2.5 x 10–21
5.0 x 10–20
2.5 x 10–19
2.2 x 10–5
2.2 x 10–20
___20. In a saturated solution of Zn(OH) 2 at 25oC the value of [OH–] is 2.0 x 10–6 M. What is the value
of the solubility-product constant, Ksp, for Zn(OH)2 at 25oC?
(A) 4.0 x 10–18
(B) 8.0 x 10–18
(C) 1.6 x 10–17
(D) 4.0 x 10–12
(E) 2.0 x 10–6
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Section II Free Response
Calculator Allowed
CLEARLY SHOW THE METHODS USED AND STEPS INVOLVED IN YOUR ANSWERS.
It is to your advantage to do this, because you may earn partial credit if you do and little or no credit if you
do not. Attention should be paid to significant figures.
C(s) + CO2(g)
2 CO(g)
1. Solid carbon and carbon dioxide gas at 1,160 K were placed in a rigid 2.00 L container, and the
reaction represented above occurred. As the reaction proceeded, the total pressure in the container
was monitored. When equilibrium was reached, there was still some C(s) remaining in the
container. Results are recorded in the table below.
Time
Total Pressure of
(hours) Gases in Container
at 1,160 K (atm)
(a)
0.0
5.00
2.0
6.26
4.0
7.09
6.0
7.75
8.0
8.37
10.0
8.37
Write the expression for the equilibrium constant, Kp , for the reaction. (1)
(b) Calculate the number of moles of CO2(g) initially placed in the container. (Assume that the
volume of the solid carbon is negligible.) (2)
(c)
For the reaction mixture at equilibrium at 1,160 K, the partial pressure of the CO2(g) is
1.63 atm. Calculate
(i)
the partial pressure of CO(g), and (1)
(ii)
the value of the equilibrium constant, Kp
(2)
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(d) If a suitable solid catalyst were placed in the reaction vessel, would the final total pressure
of the gases at equilibrium be greater than, less than, or equal to the final total pressure of the
gases at equilibrium without the catalyst? Justify your answer. (Assume that the volume of the
solid catalyst is negligible.) (1)
In another experiment involving the same reaction, a rigid 2.00 L container initially contains 10.0 g
of C(s), plus CO(g) and CO2(g), each at a partial pressure of 2.00 atm at 1,160 K.
(e) Predict whether the partial pressure of CO2(g) will increase, decrease, or remain the same as
this system approaches equilibrium. Justify your prediction with a calculation. (2)
CO2(g) + H2(g)
H2O(g) + CO(g)
2. When H2(g) is mixed with CO2(g) at 2,000 K, equilibrium is achieved according to the equation
above. In one experiment, the following equilibrium concentrations were measured.
[H2] = 0.20 mol/L
[CO2] = 0.30 mol/L
[H2O] = [CO] = 0.55 mol/L
(a) What is the mole fraction of CO(g) in the equilibrium mixture? (1)
(b) Using the equilibrium concentrations given above, calculate the value of Kc , the
equilibrium constant for the reaction.
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(c) When the system is cooled from 2,000 K to a lower temperature, 30.0 percent of the CO(g)
is converted back to CO2(g) . Calculate the value of Kc at this lower temperature. (2)
(d) In a different experiment, 0.50 mole of H2(g) is mixed with 0.50 mole of CO2(g) in a
3.0-liter reaction vessel at 2,000 K. Calculate the equilibrium concentration, in moles per
liter, of CO(g) at this temperature. (2)
9
3 H2(g) + N2(g)
2 NH3(g)
3. After 0.40 mol of N2(g) and 1.00 mol of H2(g) are placed into an evacuated 1.0 L container at
500 K, the reaction represented above occurs.
The concentration of N2(g) as a function of time is shown below.
1.00
0.80
0.60
0.40
[N2]
0.20
0
0
Time
(a) Write the expression for the equilibrium constant, Kc, for the reaction. (1)
(b) What is [N2] at equilibrium? (1)
(c) Determine the equilibrium concentrations of H2(g) and NH3(g) . (2)
(d) On the graph above make a sketch that shows how the concentrations of H2(g) and NH3(g)
change as a function of time. (2)
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(e) Calculate the value of the following equilibrium constant, Kc , at 500 K. (1)
(f) At 1500 K, the value of Kc for the reaction is 1.20. In an experiment, 0.50 mol H2(g) ,
0.80 mol N2(g) , and 0.10 mol NH3(g) are placed in a 1.0 L container and allowed to reach
equilibrium at 1500 K. Determine whether the equilibrium concentration of H2(g) will be
greater than, equal to, or less than the initial concentration of H2(g) . Justify your answer. (2)
4. Answer the following questions relating to the solubility of the sulfides of copper and silver.
(a) At 25oC, 8.8 x 10–22 g CuS(s) will dissolve in 100 mL of water.
(i)
Write the equation for the dissociation of CuS(s) in water. (1)
(ii)
Calculate the solubility, in mol∙L–1, of CuS(s) in water at 25oC. (2)
(iii)
Calculate the value of the solubility product constant, Ksp, of CuS(s) at 25oC. (1)
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(b) At 25oC, the value of Ksp for Ag2S(s) is 1.6 x 10–49 and the value of Ksp for CuS(s) is 8.5 x 10–45.
(i) Calculate the equilibrium value of [Ag+(aq)] in 1000 L of saturated Ag2S solution to
which 0.0050 mole Na2S(s) has been added. Assume no change in volume. (1)
(ii) If 9.0 mL of 0.0600 M Na2S(aq) is added to 9.0 mL of 0.0500 M AgNO3(aq), will a precipitate
form? Assume that volumes are additive. Show calculations to support your answer. (3)
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ANSWER KEY
1.
2008 #1
2.
1995
(EQUILIBRIUM)
3.
2003B #1
(edited)
4.
2001 #1
(edited)
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