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Name _____________________________________________
Date ____________________
Class ____________________
17
Chemical Equilibrium
Reviewing Vocabulary
Match the definition in Column A with the term in Column B.
Column A
Column B
_______ 1. Equilibrium reaction in which the reactants and products are
present in more than one physical state
_______ 2. A state in which the forward and reverse reactions balance each
other because they take place at equal rates
_______ 3. An equilibrium constant for the dissolving of a sparingly soluble
ionic compound in water
_______ 4. An ion that is part of two or more ionic compounds in solution
_______ 5. If a stress is applied to a system at equilibrium, the system shifts in
the direction that relieves the stress.
_______ 6. The numerical value of the ratio of product concentrations to
reactant concentrations, with the concentration of each reactant and
product raised to the power corresponding to its coefficient in the
balanced equation
a. reversible reaction
b. common ion
c. homogeneous equilibrium
d. common ion effect
e. chemical equilibrium
f. equilibrium constant
g. solubility product constant
h. Le Châtelier’s principle
i. law of chemical equilibrium
j. heterogeneous equilibrium
_______ 7. A reaction that can occur in both the forward and the reverse
directions
_______ 8. Equilibrium reaction in which all the reactants and products are in
the same physical state
_______ 9. At a given temperature, a chemical system may reach a state in
which a particular ratio of reactant and product concentrations has
a constant value.
_______ 10. The solubility of a substance is lowered because of this.
Answer the following question.
11. Explain the difference between the ion product (Qsp) and the solubility product constant (Ksp).
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Chemistry: Matter and Change
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Chapter Assessment
Name _________________________________________ Date
____________________ Class ____________________________
17
Understanding Main Ideas (Part A)
Circle the letter of the choice that best completes the statement or answers the question.
1. This is the expression for the equilibrium constant for the reaction:
CO(g) H2O(g)  CO2(g)  H2(g).
a. Keq 
[CO][H 2O]
b. K eq 
[CO2 ][H 2 ]
[CO2 ][H 2 ]
[CO][H 2O]
c. Keq 
[CO2 ]2 [H 2 ]
[CO][H 2O]2
d. K eq  [CO 2 ][H 2 ]
2. The value of any equilibrium constant is correct only at
a. a specific volume.
c. a specific concentration.
b. a specific pressure.
d. a specific temperature.
3. What is indicated by a large value for Keq?
a. A solution is saturated.
b. Products are favored in the reaction.
c. Reactants are favored in the reaction.
d. The reaction is endothermic.
4. What predicts that increasing the concentration of NH3 will shift the following reaction to the left?
N2(g)  3H2(g)  2NH3(g)
a. Le Châtelier’s principle
c. solubility product constant
b. common ion effect
d. law of chemical equilibrium
5. What will be the result if the volume of the reaction vessel is decreased for the reaction:
H2(g)  I2(g)  2HI(g)?
a. The equilibrium shifts to the left.
c. The equilibrium does not change.
b. The equilibrium shifts to the right.
d. The equilibrium constant changes.
6. The solubility product expression describes the equilibrium between a sparingly soluble ionic
compound and
a. the amount of substance added to solution.
c. its ions in solution.
b. the number of moles in the reaction.
d. the equilibrium constant.
7. What can be determined if the ion product is compared to the solubility product constant?
a. equilibrium
c. the law of mass action
b. whether a substance will precipitate
d. the volume of the solution
8. What might cause the solubility of a substance to decrease?
a. a decrease in temperature
c. the presence of a common ion
b. a decrease in pressure
d. all of the above
Chemistry: Matter and Change
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Chapter Assessment
Name _________________________________________ Date
____________________ Class ____________________________
17
Understanding Main Ideas (Part B)
For each reaction, describe how its equilibrium could be shifted in the indicated direction.
1. H2(g)  Cl2(g)  2HCl(g)  thermal energy: shift to the left
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2. C(s)  O2(g)  CO2(g)  thermal energy: shift to the right
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3. Thermal energy  8SO2(g)  S8(s)  16O2(g): shift to the right
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4. PCl5(g)  PCl3(g)  Cl2(g)  thermal energy: shift to the left
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Making predictions Given the initial concentration of two ions, predict whether they will form
a precipitate. Assume equal volumes of each solution have been mixed.
5. [Pb2]  0.700M; [F]  0.0500M; Ksp  3.3108 for PbF2
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Chemistry: Matter and Change
3
Chapter Assessment
Name _________________________________________ Date
____________________ Class ____________________________
17
Thinking Critically
The graph shows how controlling the temperature and pressure of a reaction system changes the percent
of product produced.
1. How does changing the pressure affect the amount of product produced?
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2. Is this reaction endothermic or exothermic? How do you know?
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3. If you needed to design an industrial reactor to produce the product from this reaction, what
characteristics would you want it to have?
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Chemistry: Matter and Change
4
Chapter Assessment
Name _________________________________________ Date
____________________ Class ____________________________
17
Applying Scientific Methods
When transporting food or other perishable items, more is involved than simply putting them into a
package and sealing. Some perishable items can be sensitive to changes in temperature and humidity. If
they are to stay fresh for the longest possible time, they need to be kept in a controlled environment. But,
how can this be accomplished if they are traveling in a truck through different weather conditions? Also,
when you receive your perishable product, how can you be certain that it has not been exposed to
unfavorable conditions? It’s simple. You can use equilibrium.
In water solutions, the Co 2 ion is pink. The pink color comes from the existence of the complex ion
Co(H2O)62. When Cl ions are added to it, however, this ion converts by an endothermic reaction to
Co(H2O)4Cl2, which is blue in aqueous solutions. These two species exist in equilibrium with each other.
Use your scientific skills to determine how this behavior can be used to predict changes in temperature
and humidity.
1. Write the balanced chemical equation for the endothermic equilibrium between the Co(H2O)62 and
Co(H2O)2Cl2 species. Also, note the color of each of the cobalt species. (Hint: Use Cl.)
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2. How would high humidity affect the equilibrium of the reaction?
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3. What effect would adding HCl have on the equilibrium?
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4. How might a hot day affect the equilibrium of one of these cobalt packs?
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Chemistry: Matter and Change
5
Chapter Assessment
Name _________________________________________ Date
____________________ Class ____________________________
17
Applying Scientific Methods, continued
5. Packs containing Co(H2O)Cl2 are often placed in packages to protect the items inside
from changes in humidity. Why does this work? What thing(s) might the pack have to do?
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6. When the contents of a cobalt pack turn pink, does this mean the pack can no longer take up water?
Why? What might allow the pack to take up more water?
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Chemistry: Matter and Change
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Chapter Assessment
TEACHER GUIDE AND ANSWERS
Chapter Assessment - Chapter 17 – Chemical
Equilibrium
3. The reaction will shift to the right if the temperature
is increased. It will also shift to the right if more SO2
is added or if O2 is taken away. Because S8 is a solid,
it does not affect the equilibrium in any way. The
reaction also will shift to the right if the volume is
increased because there are more moles of gaseous
product than of reactant.
4. The reaction will shift to the left if temperature is
increased. It will shift to the left if the concentration
of PCl3(g) or Cl2(g) is increased or if PCl5(g) is
decreased. To shift the reaction to the left using
pressure, decrease the volume. Making predictions
Given the initial concentration of two ions, predict
whether they will form a precipitate. Assume equal
volumes of each solution have been mixed.
5. Answer: Divide each concentration by 2
Reviewing Vocabulary
1. j
2. e
3. g
4. b
5. h
6. f
7. a
8. c
9. i
10. d
11. The ion product is the product of the concentrations
of the ions in a solution raised to the power equal to
their coefficients. It may or may not be the solubility
product constant. It equals the solubility product
constant only if the solution is saturated.
Qsp  [Pb2][F–]2  [0.350][0.0250]2
 (0.350)(6.2510–4)  2.1910–4.
Because Qsp is greater than Ksp, a precipitate will
form.
Thinking Critically
1. Increasing the pressure reduces the amount of product
produced as shown by the decrease in percent of
product as pressure increases. Increasing the pressure
means a decrease in the volume of the reaction vessel.
The stress is relieved by shifting the equilibrium to
the left because this decreases the total number
of moles.
2. This reaction is exothermic because lowering the
temperature increases the amount of product
produced. Heat is a product of the reaction. Removing
it by lowering the temperature causes the equilibrium
to shift in the direction that produces heat, relieving
the stress on the system.
3. Answers will vary. Answers should include running
the reactor at low temperatures and reduced pressure
to maximize the amount of product produced. They
may also include some method of removing product
as it is formed, which would favor its production by
shifting the equilibrium of the reaction toward the
products.
Understanding Main Ideas (Part A)
1. b
2. d
3. b
4. a
5. c
6. c
7. b
8. d
Understanding Main Ideas (Part B)
1. The reaction would go to the left if the temperature is
raised. The left direction reaction uses heat and so
relieves the stress. The left direction reaction will also
be favored if HCl is added because the left reaction
converts HCl to H2(g) and Cl2(g). Removing H2 or Cl2
also shifts the reaction to the left.
2. The reaction will shift to the right if the temperature
is decreased. The right reaction relieves the stress.
The reaction will also shift to the right if more O2(g)
is added or if CO2 is taken away. Because C(s) is a
solid, adding more of it will not change the
equilibrium. This reaction is unaffected by changes
in volume (i.e., same number of moles of gas on
each side).
Chemistry: Matter and Change
Applying Scientific Methods
1. heat  Co(H2O)62 (pink)  2Cl2 
Co(H2O)4Cl2 (blue)  2H2O
2. When the humidity is high, there is a lot of water
vapor in the air. The equation shows that adding
water shifts the equilibrium to the left. In high
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Teacher Guide and Answers
TEACHER GUIDE AND ANSWERS
humidity situations, therefore, the cobalt ion would
dominate and the solution would have a pink color.
3. Hydrochloric acid has Cl– ions, which would force
the equilibrium to the right and turn the solution a
blue color.
4. We know that the reaction is endothermic. The hotter
environment would place a stress on the system that
would cause the reaction to shift to the right and the
color would be blue. The right reaction takes up heat
and so relieves the stress.
5. Answers may vary. If a pack containing Co(H2O)Cl2
is placed in a container, it will absorb some of the
water from the air and make the air less humid. The
equilibrium in the pack will be driven to the left. This
will continue until equilibrium is achieved. The pack
would have to be designed so that it collects water
over a articular range of humidity conditions. This
could be controlled by the quantity of chemicals in
the pack.
Chemistry: Matter and Change
6. Not necessarily; the pink color only means that the
equilibrium has shifted far to the left. It does not
mean that all the water that can be absorbed has been
absorbed. Decreasing the temperature can make the
pack take up more water. Because the reaction to the
right is endothermic, the reaction to the left produces
heat. When the temperature is decreased, the reaction
to the left would dominate because it would produce
heat that would relieve the stress placed upon the
system.
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Teacher Guide and Answers