AP Chemistry – OHS – Chapter 16 Homework
Mr. Daniel
Sections 16.1 – 16.3
Due Date
1. Decide if each of the following statements is true or false. If false, change the wording to
make it true.
(a)
The magnitude of the equilibrium constant is always independent of
temperature.
(b)
When two chemical equations are added to give a net equation, the
equilibrium constant for the net equation is the product of the summed equations.
(c)
The equilibrium constant for a reaction has the same value as K for its
reverse.
(d)
Only the concentration of CO2 appears in the equilibrium constant
expression for the reaction CaCO3(s) ↔ CaO(s) + CO2(g).
(e)
For the reaction CaCO3(s) ↔ CaO(s) + CO2(g), the value of K is
numerically the same whether the amount of CO2 is expressed as moles per liter or
as gas pressure.
3. The decomposition of calcium carbonate is an endothermic process:
CaCO3(s) ↔ CaO(s) + CO2(g)
a) Using Le Chatelier’s principle, explain how increasing the temperature would
affect the equilibrium.
b) If more CaCO3 is added to a flask in which the equilibrium exists, how is the
equilibrium affected?
c) What if some additional CO2 is placed in the flask?
5. If the reaction quotient (Q) is smaller than the equilibrium constant(K)for a reaction such
as A ↔ B, does this mean that reactant A continues to be consumed to form B, or does B
form A, as the system moves to equilibrium? Explain the reason for your answer.
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Writing Equilibrium Constant Expressions
7. Which of the following is the correct form of the equilibrium constant expression for the
reaction of iron(II) ion with tin?
Fe2+(aq) + Sn(s) ↔ Sn2+(aq) + Fe(s)
(a)
(b)
(c)
(d)
K = [Sn2+][Fe]/[Fe2+][Sn]
K = [Fe2+][Sn]/[Sn2+][Fe]
K = [Fe]/[Sn]
K = [Sn2+]/[Fe2+]
9. Write equilibrium constant expressions for the following reactions. For gases use either
pressure or concentrations.
(a) 3 O2(g) ↔ 2 O3(g)
(b) Fe(s) + 5 CO(g) ↔ Fe(CO)5(g)
(c) (NH4)2CO3(s) ↔ 2 NH3(g) + CO2(g) + H2O(g)
(d) Ag2SO4(s) ↔ 2 Ag+(aq) + SO42−(aq)
The Reaction Quotient
11. The reaction…
2 NO2(g) ↔ N2O4(g)
…has an equilibrium constant, K, of 171 at 25°C. If 2.0 × 10−3 mol of NO2 is present in a
10.0 L flask along with 1.5 × 10−3 mol of N2O4, is the system at equilibrium? If it is not at
equilibrium, does the concentration of NO2 increase or decrease as the system proceeds to
equilibrium? Explain why.
12. A mixture of SO2, O2 and SO3 at 1000 K contains the gases at the following
concentrations: [SO2] = 5.0 × 10−3 mol/L, [O2] = 1.9 × 10−3 mol/L, and [SO3] = 6.9 × 10−3.
Is the reaction at equilibrium? If not, which way will the reaction proceed to reach
equilibrium?
2 SO2(g) + O2(g) ↔ 2 SO3(g)
K = 279.
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13. The equilibrium constant, K, for the reaction…
2 NOCl(g) ↔ 2 NO(g) + Cl2(g)
is 3.9 × 10−3 at 300°C. A mixture contains the gases at the following concentrations:
[NOCl] = 5.0 × 10−3 mol/L, [NO] = 2.5 × 10−3 mol/L, and [Cl2] = 2.0 × 10−3 mol/L.
Is the reaction at equilibrium at 300°C? If not, in which direction does the reaction proceed
to come to equilibrium? Explain your answer.
Calculating an Equilibrium Constant
15. An equilibrium mixture of SO2, O2, and SO3 at 1000 K contains the gases at the
following concentrations: [SO2] = 3.77 × 10−3 mol/L. [O2] = 4.30 × 10−3 mol/L, and [SO3]
= 4.13 × 10−3 mol/L. Calculate the equilibrium constant, K, for the reaction
2 SO2(g) + O2(g) ↔ 2 SO3(g)
Sections 16.4 – 16.7
Due Date
Using Equilibrium Constants
21. Cyclohexane, C6H12, a hydrocarbon, can isomerizes into methylcyclopentane, a
compound of the same formula (C5H9CH3) but with a different molecular structure.
The equilibrium constant has been estimated to be 0.12 at 25°C.
If you originally placed 0.045 mol of cyclohexane in a 2.8-L
flask, what are the concentrations of cyclohexane and
methylcyclopentane when equilibrium is established? Use the
“ICE” format to calculate your answer
C6H12
↔
C5H9CH3
[I]
[C]
[E]
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23. The equilibrium constant for the reaction N2O4(g) ↔ 2 NO2(g)
at 25°C is 5.88 × 10−3. Suppose 15.6 g of N2O4 is placed in a 5.00-L flask at 25°C.
N2O4(g)
↔
2 NO2(g)
[I]
[C]
[E]
(a) Calculate: The number of moles of NO2 present in equilibrium.
(b) The percentage of the original N2O4 that is dissociated.
25. Iodine dissolves in water, but its solubility in a nonpolar solvent such as CCl4 is greater.
The equilibrium constant is 85.0 for the reaction
I2(aq) ↔ I2(CCl4)
You place 0.0340 g of I2 in 100.0 mL of water. After
shaking it with 10.0 mL of CCl4, how much I2 remains in
the water layer?
I2(aq)
↔
I2(CCl4)
[I]
[C]
[E]
Balanced Equations & Equilibrium Constants
27. Which of the following correctly relates the two equilibrium constants for the two
reactions shown?
A + B ↔ 2C
K1
C ↔ ½ A + ½ B K2
(a) K2 = 1/(K1)1/2
(b) K2 = 1/K1
(c) K2 = K12
(d) K2 = −K11/2
29. The equilibrium constant K for the following reaction is 6.66 × 10−12 at 1000 K.
CO2(g) ↔ CO(g) + ½ O2(g)
Calculate K for the reaction:
2 CO(g) + O2(g) ↔ 2 CO2(g)
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31. Calculate K for the reaction:
Fe(s) + H2O(g) ↔ FeO(s) + H2(g)
given the following information:
H2O(g) + CO(g) ↔ H2(g) + CO2(g)
FeO(s) + CO(g) ↔ Fe(s) + CO2(g)
K = 1.6
K = 0.67
Disturbing a Chemical Equilibrium
33. KP for the following reaction is 0.16 at 25°C.
2 NOBr(g) ↔ 2 NO(g) + Br2(g)
The enthalpy change for the reaction at standard conditions is + 16.1 kJ. Predict which way
the equilibrium will shift (left, right, or no change) when each of the following changes is
made and explain why:
(a) Adding more Br2(g)
(b) Removing some NOBr(g)
(c) Decreasing the temperature
(d) Increasing the container volume
35. The decomposition of NH4HS is an endothermic process:
NH4HS(s) ↔ NH3(g) + H2S(g)
b) Using Le Chatelier’s principle, explain how increasing the temperature would
affect the equilibrium.
c) If more NH4HS is added to a flask in which this equilibrium exists, how is the
equilibrium affected?
d) What if some additional NH3 is placed in the flask?
e) What will happen to the pressure of NH3 if some H2S is removed from the flask?
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General Questions
Due Date
37. The equilibrium constant for the reaction below is 1.7 × 10−3 at 2300 K.
N2(g) + O2(g) ↔ 2 NO(g)
(a) What is K for the reaction when it is written as:
½ N2(g) + ½ O2(g) ↔ NO(g)
(b) What is K for the reaction:
2 NO(g) ↔ N2(g) + O2(g)
43. The equilibrium constant for the butane ↔ isobutane isomerization reaction is 2.5 at 25°C .
C4H10
↔
C3H7CH3
a) If 1.75 mol of butane and 1.25 mol of isobutane are mixed a 1 liter container, is
the system at equilibrium? If not, when it proceeds to equilibrium which reagent
increases in concentration?
b) Calculate the concentrations of the two compounds when the system reaches
equilibrium? Remember to ICE.
47. Heating a metal carbonate leads to decomposition.
BaCO3(s) ↔ BaO(s) + CO2(g)
Predict the effect on the equilibrium of each change listed here. Answer by choosing (i) no
change, (ii) shifts left, or (iii) shifts right. Give a reason for each of your answers.
(a) Add BaCO3.
(b) Add CO2.
(c) Add BaO.
(d) Raise the temperature.
(e) Increase the volume of the flask containing the reaction.
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53. Ammonium iodide dissociates reversibly to ammonia and hydrogen iodide if the salt is
heated to a sufficiently high temperature.
NH4I(s) ↔ NH3(g) + HI(g)
Some ammonium iodide is placed in a flask, which is then heated to 400°C. If the total
pressure in the flask when equilibrium has been achieved is 705 mm Hg, what is the value
of KP (when partial pressures are in atmospheres)?
59. Kc for the decomposition on ammonium hydrogen sulfide is 1.8 × 10−4 at 25°C.
NH4HS(s) ↔ NH3(g) + H2S(g)
(a) When the pure salt decomposes in a flask, what are the equilibrium concentrations
of NH3 and H2S?
(b) If NH4HS is placed in a flask already containing 0.020 mol/L of NH3 and then the
system is allowed to come to equilibrium, what are the equilibrium concentrations
of NH3 and H2S? (ICE)
65. The ammonia complex of trimethylborane, (H3N)B(CH3)3, dissociates at 100°C to its
components with Kp = 4.62.
If NH3 is changed to some other molecule, the
equilibrium constant is different.
For [(CH3)3P]B(CH3)3
For [(CH3)3N]B(CH3)3
For (H3N)B(CH3)3
Kp = 0.128
Kp = 0.472
Kp = 4.62
(a) If you begin an experiment by placing 0.010 mol of each complex in a flask, which
would have the largest partial pressure of B(CH3)3 at 100°C?
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(b) If 0.73 g (0.010 mol) of (NH3)B(CH3)3 is placed in a 100.-mL flask and heated to
100°C, what is the partial pressure of each gas in the equilibrium mixture and what
is the total pressure?
(c) What is the percent dissociation of (NH3)B(CH3)3?
69. At 1800 K, oxygen dissociates very slightly into its atoms.
O2(g) ↔ 2 O(g)
Kp = 1.2 × 10−10
If you place 1.0 mole of O2 in a 10.-L vessel and heat it to 1800 K, how many O atoms are
present in the flask when equilibrium is achieved?
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