Name: ___________________
Problem Set – Chapter 7 –Chemical Equilibrium
Knowledge
Inquiry
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Communication
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Application
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1. A 2.0L flask contains 2.0 x 10-3M H2 (g), 2.0 x 10-3MCl2(g) and 2.0 x 10-3M HCl (g) at equilibrium.
This system is represented by the following chemical equation: H2 (g) + Cl2 (g)  2 HCl (g).
Calculate the equilibrium constant for this reaction.
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2. Sketch each graph to show how concentrations change as equilibrium is approached
[Reactant]
[Product]
Overall Rate
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3.



Label each graph with the correct description.
The forward and reverse rates as equilibrium is approached
The overall rate as equilibrium is approached
The reactant and product concentrations as equilibrium is approached (two graphs)
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Knowledge
Inquiry
Communication
Application
4. One mole of very cold, colorless N2O4 (g) is placed into a 1.0L glass container of room temperature.
The reaction:
N2O4 (g)
⇄
2 N02 (g)
H= +58 KJ
(colorless)
(brown)
proceeds to equilibrium. The concentration of each gas is measured as a function of time.
Time (s)
[N2O4] (M)
[N02] (M)
0
1.0
0.0
5
0.83
0.34
10
0.81
0.38
15
0.80
0.40
20
0.80
0.40
25
0.80
0.40
a) Plot concentration of N2O4 and N02 against time on the same graph below.
1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 0
5
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10
15
20
TIME (s)
25
30
35
b) After what time interval has equilibrium been established? ___________
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c) Describe the change in the appearance of the container over 25 seconds (describe the colour change
and when it becomes constant).
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d) What are the equilibrium concentrations of N2O4 and N02?
[N2O4]= ______
[N02] = ______
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e) Is the reaction over, when equilibrium has been achieved? If not, explain.
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Knowledge
Inquiry
Communication
Application
5. What are the necessary conditions to establish equilibrium?
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6. What are the characteristics of an equilibrium system?
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7. Describe the changes that occur after each stress is applied to the equilibrium.
N2 (g) +
Stress
[N2]
3H2 (g)
⇄
[H2]
2NH3(g) + 92 KJ
[NH3]
Shifts
Right or Left
Shifts to the
Reactants or Product
a) [N2] is increased
b) [NH3] is decreased
c) Temp is decreased
d) A catalyst is added
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8. Consider the equilibrium that follows:
Cu+ (aq) + Cl-(aq) ⇄ CuCl (s)
(green)
ΔH = + 98 kJ
Describe how the above equilibrium will shift after each stress below:
Cu+ is green
shift
color change
Increase in temperature
Increase [HCl]
Add NaCl
Add NaOH (aq)
(check your solubility table for a possible reaction)
Add CuCl(s)
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Add AgNO3 (aq)
Knowledge
Inquiry
Communication
Application
9. Consider the following equilibrium system.
I2(g)
+
Cl2(g)
⇄ 2 ICl (g) + energy
Label the graph that best represents each of the following stresses and shift.
 adding I2(g)
 increasing the temperature
 increasing the volume
 removing Cl2(g)
I2
I2
ICl
ICl
I2
I2
ICl
Cl2
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10. Describe four ways of increasing the yield of for the reaction below:
N2O4(g)
+ 59 KJ ⇄
2 NO2(g)
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Knowledge
Inquiry
Communication
Application
11. Keq= 798 at 25oC for the reaction: 2SO2 (g) + O2 (g) ⇄ 2SO3 (g).
In a particular mixture at equilibrium, [SO2]= 4.20 M and [SO3]=11.0M. Calculate the equilibrium
[O2] in this mixture at 25oC.
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12.
4.00 moles of SO2 and 5.00 moles O2 are present in a 2.00 L container at 100oC and are at
equilibrium. Calculate the equilibrium concentration of SO3 and the number of moles SO3
present if the Keq = 1.47 x 10-3.
2 SO3(g)
⇄
2 SO2(g)
+
O2(g)
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13.
1.60 moles CO and 1.60 moles H2O are placed in a 2.00 L container at 690 oC . (Keq = 10.0).
CO (g) + H2O (g) ⇄ CO2 (g) + H2 (g)
Calculate all equilibrium concentrations.
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14.
For the reaction: CO(g) + H2O(g) ⇄ CO2(g) + H2(g)
Keq= 10.0 at 690 oC. The following
concentrations were observed: [CO]=2.0 M, [H2]= 1.0 M, [CO2]=2.0 M, [H2O] = 0.10 M. Is
the reaction at equilibrium? If not, how will it shift in order to get to equilibrium?
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Knowledge
Inquiry
Communication
Application
15.
Hydrogen, a potential fuel, is found in great abundance in water. Before the hydrogen can be
used as a fuel however, it must be separated from the oxygen; the water must be split into H2
and O2. One possibility is thermal decomposition, but this requires very high temperatures.
Even at 1000C, Kc = 7.3 x 10-18 for the reaction.
2H2O (g)  2 H2 (g) + O2 (g)
If at 1000C the H2O (g) concentration is initially at 0.100M, what will the H2 concentration
be when the reaction reaches equilibrium?
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16. At a certain temperature the Keq for a reaction is 75. 2O3(g) ⇄ 3O2(g)
Predict the direction in which the equilibrium will proceed, if any, when the following amounts
are introduced to a 10 L vessel.
a) 0.60 mole of O3 and 3.0 mol of O2
b) 0.050 mole of O3 and 7.0 mol of O2
c) 1.5 mole of O3 and no O2
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17.
A student determines that the solubility of magnesium carbonate, MgCO3 (s), in water at a
certain temperature is 2.63 x 10-3 mol/L.
a. What is the Ksp for magnesium carbonate?
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Knowledge
Inquiry
Communication
Application
b. The student plans to mix 250.0 mL of a 0.0035 M solution of sodium carbonate Na2CO3
(aq) and 500.0 mL of a 0.0090 M solution of magnesium chloride, MgCl2 (aq). Determine
whether a precipitate of MgCO3 will form.
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18. a. Calculate the molar solubility of lead (II) chloride, PbCl2 at SATP, in pure water.
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b. What is the molar solubility of PbCl2 in a 0.2mol/L NaCl solution at SATP?
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c. Explain why the two molar solubility values are different in a and b.
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19.
In the reaction: A + B ⇄ C + D + 100 kJ, what happens to the value of Keq if we increase the
temperature? Explain
20.
If the value of Keq decreases when we decrease the temperature, is the reaction exothermic or
endothermic? Explain.
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Knowledge
Inquiry
Communication
Application
21.
Consider the following equilibrium system:
N2(g) + 3H2(g) 
2NH3(g) + energy
A 1.00 L container is filled with 7.0 moles NH3 and the system proceeds to equilibrium as
indicated by the graph.
8.0
M
6.0
4.0
2.0
NH3
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a)
Draw and label the graph for N2 and H2. Fill in a RICE chart if you are not sure
how to do this.
N2(g) + 3H2(g) 
2NH3(g)
R
I
C
E
b)
Calculate the Keq for the above reaction.
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Knowledge
Inquiry
Communication
Application