Equilibrium Practice Test
Multiple Choice
Identify the choice that best completes the statement or answers the question.
____
1. A reaction in which products can react to re-form reactants is
a. reforming.
c. buffered.
b. reversible.
d. impossible.
____
2. At equilibrium,
a. all reactions have ceased.
b. only the forward reaction continues.
c. only the reverse reaction continues.
d. both the forward and reverse reactions continue.
____
3. What symbol in a chemical equation indicates equilibrium?
a.
c.
b.
d. None of the above
____
4. What two processes are at equilibrium in a saturated sugar solution?
a. evaporation and condensation
c. decomposition and synthesis
b. dissolving and crystallization
d. ionization and recombination
____
5. What symbol represents the equilibrium constant?
a. k
c. c
b. K
d. R
____
6. A very high value of K indicates that
a. equilibrium is reached slowly.
b. products are favored.
c. reactants are favored.
d. equilibrium has been reached.
____
7. The value of K for a system
a. can be calculated from the molar masses of products and reactants.
b. can be calculated from the enthalpies of the forward and reverse reactions.
c. can be calculated from the chemical properties of products and reactants.
d. must be measured by experiment.
____
8. In the equation
____
, what represents the concentrations of the reactants?
a. [Y] and [Z]
c.
b. [W] and [X]
d.
9. An equilibrium mixture of SO2, O2, and SO3 gases at 1500 K is determined to consist of 0.344 mol/L SO2,
0.172 mol/L O2, and 0.56 mol/L SO3. What is the equilibrium constant for the system at this temperature? The
balanced equation for this reaction is
2SO2(g) + O2(g)
2SO3(g).
a. 0.41
c. 6.7
b. 2.8
d. 15
____ 10. If the pressure on the equilibrium system 2CO(g) + O2(g)
a. the quantity of CO(g) increases.
b. the quantity of CO2(g) decreases.
c. the quantity of CO2(g) increases.
d. the quantities in the system do not change.
2CO2(g) is increased,
____ 11. If the temperature of the equilibrium system CH3OH(g) + 101 kJ
CO(g) + 2H2(g) increases, K
a. increases.
c. increases or decreases.
b. decreases.
d. does not change.
____ 12. If a reaction system has come to equilibrium, it can be made to run to completion
a. only if it is not reversible.
c. by removing a product.
b. only if the temperature is low enough.
d. under no circumstances.
____ 13. If a soluble product forms, a reaction may run to completion
a. if the product is only slightly ionized.
b. if the product is highly soluble.
c. if the product is not gaseous.
d. under no circumstances.
____ 14. Which reaction tends to run to completion?
a. K+(aq) +
(aq)
KCl(s)
b. 2NO2(g)
N2O4(g)
c. Ag+(aq) +
(aq)
AgCl(s)
d. H2(g) + I2(g)
2HI(g)
____ 15. Adding a charged particle common to two solutes decreases solute concentration. This observation
demonstrates
a. the common-ion effect.
c. hydrolysis.
b. Le Châtelier's principle.
d. buffering.
____ 16. The common-ion effect
a. promotes condensation.
b. promotes evaporation.
c. reduces ionization.
d. increases solubility.
____ 17. Adding sodium acetate to an acetic acid, CH3COOH, solution
a. increases pH and lowers [H+].
b. increases pH and raises [H+].
c. decreases pH and lowers [H+].
d. decreases pH and raises [H+].
____ 18. In the equilibrium system CH3COOH(aq) + H2O(l)
H3O+(aq) + CH3COO–(aq), which species is present
in the highest concentration at equilibrium?
a. CH3COOH
b. H3O+
c. CH3COO–
d. Equal concentrations of CH3COOH, H3O+ and CH3COO– are present.
____ 19. What is the acid-ionization expression for the ionization of acetic acid, shown in the reaction represented by
the equation CH3COOH(aq) + H2O(l)
H3O+(aq) + CH3COOH–(aq)?
a. [H3O+] [CH3COOH–]
c.
b.
d.
____ 20. To what degree does water ionize?
a. completely
b. to a large extent
c. slightly
d. not at all
____ 21. A chemical reaction is in equilibrium when
a. forward and reverse reactions have ceased.
b. the equilibrium constant equals 1.
c. forward and reverse reaction rates are equal.
d. no reactants remain.
____ 22. Which change can cause the value of the equilibrium constant to change?
a. temperature
b. concentration of a reactant
c. concentration of a product
d. none of the above
____ 23. Consider the following reaction:
2C(s) + O (g)
2CO(g)
The equilibrium constant expression for this reaction is —
a.
b.
c.
d.
Choose the best answer from the options that follow each question.
____ 24. In a bottle of unopened cola, the CO2 gas dissolved in the liquid is in equilibrium with the CO2 gas above the
liquid. The dissolved gas reacts with water molecules in the cola to form carbonic acid, which also dissociates
into carbon dioxide and water. Which chemical equation(s) best describe this equilibrium system?
a. CO2(g)  CO2(l)
b. CO2(g)  CO2(aq) and CO2(l) + H2O(l)  H2CO3(aq)
c. CO2(g)  CO2(aq)
d. CO2(g)  CO2(aq) and CO2(aq) + H2O(l)  H2CO3(aq)
____ 25. Which of the following would not affect the aqueous equilibrium reaction represented by the equation below?
HNO2(aq)  H+(aq) + NO (aq)
a. the addition of NaNO3(s)
b. an increase in H+ concentration
c. the addition of NaNO2(s)
d. a decrease in NO concentration
____ 26. Consider the equilibrium system represented by the equation below.
H2O(l) + 2CrO (aq)  Cr2O (aq) + 2OH (aq)
yellow
orange
If the hydroxide ions were removed, how would the color change?
a. to darker yellow
b. to lighter orange
c. to darker orange
d. not at all
____ 27. The common-ion effect promotes
a. dissolution.
b. precipitation.
c. boiling.
d. ionization.
PART I Choose the best answer from the options that follow each question.
____ 28. What is the effect on concentration if more CO(g) is added to the following equilibrium system?
2CO(g) + O2(g)  2CO2(g)
a. [CO2] increases and [O2] decreases.
b. Both [CO2] and [O2] increase.
c. Both [CO2] and [O2] decrease.
d. Both [CO2] and [O2] remain the same.
____ 29. A very high value for K indicates that
a. reactants are favored.
b. products are favored.
c. equilibrium is reached slowly.
d. equilibrium has been reached.
Short Answer
1. Sulfur dioxide is commonly formed by the burning of fossil fuels. It combines with additional oxygen to form
sulfur trioxide. Write an equilibrium expression for the reaction represented by the following equation.
2SO2(g) + O2(g)
2SO3(g)
2. Why are equilibrium expressions not written for reactions that go to completion?
3. Explain why the following reaction goes to completion instead of to equilibrium.
Mg(s) + 2HCl(aq)
MgCl2(aq) + H2(g)
PART III
Write the answers to the following questions in the space provided.
4. Name three ways that chemical equilibrium can be disturbed.
5. Describe three situations in which ionic reactions go to completion.
In the space provided, predict the effect that decreasing pressure would have on each of the following
reaction systems at equilibrium.
6. H2(g) + Cl2(g)  2HCl(g)
7. 3O2(g)  2O3(g)
8. CaCO3(s)  CaO(s) + CO2(g)
PART IV Write the answers to the following problems below, and show your work in the space
provided.
9. At equilibrium a 1.0 L vessel contains 20.0 mol of H2, 18.0 mol of CO2, 12.0 mol of H2O, and 5.9 mol of CO
at 427°C. Calculate K at this temperature for the reaction described by the equation
CO2(g) + H2(g)  CO(g) + H2O(g).
10. Use the reaction E + F  2G and the equilibrium concentrations 0.60 mol/L for E, 0.80 mol/L for F, and 1.30
mol/L for G to calculate the equilibrium constant. E, F, and G are all gases.
11. What is the concentration of H3O+ ions in a solution of an acid HY that ionizes to produce H3O+ and Y ions?
Ka is 4.32 10 5, and the final concentration of HY is 7.40 10 2 mol/L.
Essay
1. Explain why the figure below is an example of a system at equilibrium.
Problem
1. Calculate K for the synthesis of ammonia at 400°C,
, if the following concentrations are present at equilibrium: N2(g) = 1.2 mol/L,
H2(g) = 0.80 mol/L, and NH3(g) = 0.28 mol/L.
2. At 2000°C, carbon dioxide decomposes as shown.
2CO2(g)
2CO(g) + O2(g)
If K is 6.4 107 and the concentrations of CO(g) and O2(g) are 2.0 103 mol/L and 1.0
equilibrium, respectively, calculate the concentration of carbon dioxide.
103 mol/L at
3. Phenol, C6H5OH, partially dissociates in water as shown.
C6H5OH(aq) + H2O(l)
H3O+(aq) + C6H5O(aq)
If Ka is 1.6 1010 and the concentrations of H3O+(aq) and C6H5O(aq) are both 1.0
what would be the concentration of phenol?
4. At 1200°C, K is 2.6 103 for the dissociation of iodine molecules. I2(g)
concentration of I2(g) is 0.95 mol/L, what is the concentration of I(g)?
105 M at equilibrium,
2I(g) If the equilibrium
5. Calculate the H3O+ concentration in a solution of acetic acid if the concentration of molecular acetic acid
present at equilibrium is 9.97 103 M and K for the dissociation is 1.86 105. CH3COOH(aq) + H2O(l)
H3O+(aq) + CH3COO(aq)
Completion
Complete each statement.
PART II Write the correct term (or terms) in the space provided.
1. The ____________________ is the phenomenon in which the addition of a charged particle common to two
solutes decreases the solute concentration.
2. The equilibrium constant equation for the reaction NH3(g) + H2O(l)  NH (aq) + OH (aq) is Kb =
____________________.
3. If the temperature of an equilibrium system is decreased, the ____________________ reaction will be
favored.
Equilibrium Practice Test
Answer Section
MULTIPLE CHOICE
1. ANS: B
PTS: 1
DIF:
REF: d37d958b-f97e-11de-9c72-001185f0d2ea
2. ANS: D
PTS: 1
DIF:
REF: d3825a45-f97e-11de-9c72-001185f0d2ea
3. ANS: D
PTS: 1
DIF:
REF: d384e3b2-f97e-11de-9c72-001185f0d2ea
4. ANS: B
PTS: 1
DIF:
REF: d3871eff-f97e-11de-9c72-001185f0d2ea
5. ANS: B
PTS: 1
DIF:
REF: d389a86c-f97e-11de-9c72-001185f0d2ea
6. ANS: B
PTS: 1
DIF:
REF: d390a873-f97e-11de-9c72-001185f0d2ea
7. ANS: D
PTS: 1
DIF:
REF: d3930ad0-f97e-11de-9c72-001185f0d2ea
8. ANS: A
PTS: 1
DIF:
REF: d395943d-f97e-11de-9c72-001185f0d2ea
9. ANS: D
Solution:
10.
11.
12.
13.
14.
15.
16.
17.
18.
PTS:
OBJ:
ANS:
REF:
ANS:
REF:
ANS:
REF:
ANS:
REF:
ANS:
REF:
ANS:
REF:
ANS:
REF:
ANS:
REF:
ANS:
REF:
1
DIF: III
REF:
3
C
PTS: 1
DIF:
d39f1db1-f97e-11de-9c72-001185f0d2ea
A
PTS: 1
DIF:
d3a3bb5b-f97e-11de-9c72-001185f0d2ea
C
PTS: 1
DIF:
d3a88015-f97e-11de-9c72-001185f0d2ea
A
PTS: 1
DIF:
d3ad44cf-f97e-11de-9c72-001185f0d2ea
C
PTS: 1
DIF:
d3afce3c-f97e-11de-9c72-001185f0d2ea
A
PTS: 1
DIF:
d3b23099-f97e-11de-9c72-001185f0d2ea
C
PTS: 1
DIF:
d3b6ce43-f97e-11de-9c72-001185f0d2ea
A
PTS: 1
DIF:
d3bb92fd-f97e-11de-9c72-001185f0d2ea
A
PTS: 1
DIF:
d3c057b7-f97e-11de-9c72-001185f0d2ea
I
OBJ: 1
I
OBJ: 1
I
OBJ: 1
I
OBJ: 1
I
OBJ: 2
I
OBJ: 2
I
OBJ: 2
II
OBJ: 3
d39c9444-f97e-11de-9c72-001185f0d2ea
II
OBJ: 1
II
OBJ: 1
I
OBJ: 2
I
OBJ: 2
II
OBJ: 2
I
OBJ: 3
I
OBJ: 3
II
OBJ: 3
II
OBJ: 1
19. ANS:
REF:
20. ANS:
REF:
21. ANS:
22. ANS:
23. ANS:
24. ANS:
25. ANS:
26. ANS:
27. ANS:
28. ANS:
29. ANS:
C
PTS: 1
DIF:
d3c51c71-f97e-11de-9c72-001185f0d2ea
C
PTS: 1
DIF:
d3c9e12b-f97e-11de-9c72-001185f0d2ea
C
PTS: 1
TOP:
A
PTS: 1
TOP:
B
PTS: 1
TOP:
D
PTS: 1
TOP:
A
PTS: 1
TOP:
C
PTS: 1
TOP:
B
PTS: 1
TOP:
A
PTS: 1
TOP:
B
PTS: 1
TOP:
II
OBJ: 1
I
OBJ: 2
Chemistry Chapter 18 - Standardized Test Practice
Chemistry Chapter 18 - Standardized Test Practice
Chemistry Chapter 18 - Standardized Test Practice
Chapter 18 Test A
Chapter 18 Test A
Chapter 18 Test A
Chapter 18 Test A
Chapter 18 Test B
Chapter 18 Test B
SHORT ANSWER
1. ANS:
PTS: 1
DIF: II
REF: d40805ad-f97e-11de-9c72-001185f0d2ea
OBJ: 3
2. ANS:
The final concentration of reactants for a reaction going to completion is zero. Equilibrium is not reached.
PTS: 1
DIF: II
REF: d40a40fa-f97e-11de-9c72-001185f0d2ea
OBJ: 3
3. ANS:
The hydrogen gas escapes if the system is not closed.
PTS: 1
DIF: III
REF: d40ca357-f97e-11de-9c72-001185f0d2ea
OBJ: 2
4. ANS:
changes in concentration, changes in pressure, changes in temperature
PTS: 1
TOP: Chapter 18 Test B
5. ANS:
If a product is precipitated as a solid; if a gaseous product forms and escapes; if a soluble product is only
slightly ionized
PTS: 1
6. ANS:
none
TOP: Chapter 18 Test B
PTS: 1
TOP: Chapter 18 Test B
7. ANS:
reverse reaction is favored
PTS: 1
TOP: Chapter 18 Test B
8. ANS:
forward reaction is favored
PTS: 1
9. ANS:
0.20
TOP: Chapter 18 Test B
PTS: 1
10. ANS:
3.5
TOP: Chapter 18 Test B
PTS: 1
11. ANS:
1.79 10
TOP: Chapter 18 Test B
PTS: 1
3
mol/L
TOP: Chapter 18 Test B
ESSAY
1. ANS:
The fish moving back and forth between two fishbowls represent the equilibrium. The contents of the system
are constant. There are equal numbers of fish in each bowl, but they are not the same fish from moment to
moment. The number of fish moving to the bowl on the left equals the number of fish moving to the bowl on
the right.
PTS: 1
OBJ: 1
DIF: I
REF: d40cca67-f97e-11de-9c72-001185f0d2ea
DIF: II
REF: d40f05b4-f97e-11de-9c72-001185f0d2ea
PROBLEM
1. ANS:
PTS: 1
OBJ: 3
2. ANS:
PTS: 1
OBJ: 3
3. ANS:
DIF: II
REF: d4116811-f97e-11de-9c72-001185f0d2ea
PTS: 1
OBJ: 3
4. ANS:
DIF: II
REF: d4118f21-f97e-11de-9c72-001185f0d2ea
PTS: 1
OBJ: 1
5. ANS:
DIF: II
REF: d413ca6e-f97e-11de-9c72-001185f0d2ea
PTS: 1
OBJ: 1
DIF: II
REF: d413f17e-f97e-11de-9c72-001185f0d2ea
COMPLETION
1. ANS: common-ion effect
PTS: 1
TOP: Chapter 18 Test B
2. ANS: K =
PTS: 1
3. ANS: exothermic
TOP: Chapter 18 Test B
PTS: 1
TOP: Chapter 18 Test B