Name Date Class
CHAPTER 18 STUDY GUIDE FOR CONTENT MASTERY
Chemical Equilibrium
Section 18.1 Equilibrium: A State of Dynamic Balance
In your textbook, read about chemical equilibrium.
Complete each statement.
1. When a reaction results in almost complete conversion of reactants to products, chemists
say the reaction goes to completion .
2. A reaction that can occur in both the forward and the reverse directions is called a(n)
reversible reaction
.
chemical equilibrium
3. is a state in which the forward and reverse reactions balance
each other because they take place at equal rates.
4. At equilibrium, the concentrations of reactants and products are
constant ,
but that does not mean that the amounts or concentrations are equal .
5. Equilibrium is a state of action , not one of inaction .
In your textbook, read about equilibrium expressions and constants.
Copyright © Glencoe/McGraw-Hill, a division of the McGraw-Hill Companies, Inc.
For each statement below, write true or false.
F 6. The law of chemical equilibrium states that at a given pressure, a chemical
system may reach a state in which a particular ratio of reactant to product
concentrations has a constant value.
T 7. The equation H2(g) I2(g) 3 2HI(g) is an example of a homogeneous
T equilibrium.
8. If an equilibrium constant has a value less than one, the reactants are
favored at equilibrium.
F 9. The value for Keq is constant only at a specific volume.
F
10. If the equilibrium constant for a reaction at 300 K is 49.7, the
concentration of the reactants will be greater than the concentration of
the products.
T
11. A heterogeneous equilibrium means that reactants and products are
present in more than one state.
T
12. The product of the forward chemical reaction is HI, for the equilibrium
expression:
[HI]2
Keq
[H2][I2]
Study Guide for Content Mastery Chemistry: Matter and Change • Chapter 18 103
Name Date Kc = ([SO3]^2/([SO2]^2[O2]))
Class
CHAPTER 18 STUDY GUIDE FOR CONTENT MASTERY
Section 18.1 continued
In your textbook, read about determining equilibrium constants.
A chemist did two experiments to determine the equilibrium constant for the reaction of
sulfur dioxide with oxygen to form sulfur trioxide. Use the table showing the results of
the experiments to answer the following questions.
2SO2(g) O2(g) 3 2SO3(g) at 873 K
Experiment 1 Experiment 2
Initial concentrations Equilibrium concentrations Initial concentrations Equilibrium concentration
[SO2] 2.00M [SO2] 1.50M [SO2] 0.500M [SO2] 0.590M
[O2] 1.50M [O2] 1.26M [O2] 0M [O2] 0.0450M
[SO3] 3.00M [SO3] 3.50M [SO3] 0.350M [SO3] 0.260M
13. Write the equation to calculate the equilibrium constant for the reaction.
Keq=(SO3)^2/(SO2)^2(O2)
14. Is this reaction an example of a homogeneous or heterogeneous equilibrium?
homogenous
15. Calculate the equilibrium constant from the data obtained in experiment 1.
Keq=4.32
(3.50)^2/(1.50)^2 (1.26)=4.32098 = 4.32
Copyright © Glencoe/McGraw-Hill, a division of the McGraw-Hill Companies, Inc.
16. What is the equilibrium constant for the reaction in experiment 2?
17. Was it necessary to calculate both equilibrium constants? Why or why not?
No both expiriments were done at the same temperature
18. What does this experiment show about the initial concentrations of products and reac-
tants in a reversible reaction?
It shows ir does not matter what the initial concentrations of products and reactants are in
a reversible reaction
104 Chemistry: Matter and Change • Chapter 18 Study Guide for Content Mastery
Name Date Class
CHAPTER 18 STUDY GUIDE FOR CONTENT MASTERY
Section 18.2 Factors Affecting Chemical Equilibrium
In your textbook, read about Le Châtelier’s Principle.
Answer the following questions.
1. What does Le Châtelier’s Principle say?
when stress is applied to system at equilibrium the system shifts in the side the relieves it
2. What are three kinds of stresses that can be placed on a system?
concentration, temperature, and pressure
For each reaction below, state the direction, left or right, in which the equilibrium will
shift when the indicated substance is added. Identify one other way in which the reaction
could be shifted in the same direction you indicated. (Hint: There may be more than one
way to do this.)
3. Reaction: N2(g) 3H2(g) 3 2NH3(g); NH3 added
remove N2 or H2, left
4. Reaction: H2(g) I2(g) 3 2HI(g); H2 added
add I2 or remove HI, right
Copyright © Glencoe/McGraw-Hill, a division of the McGraw-Hill Companies, Inc.
5. Reaction: CO(g) H2O 3 CO2(g) H2(g); H2O added
add CO or remove CO2 or H2, right
6. Reaction: 2SO2(g) O2(g) 3 2SO3(g); SO3 added
remoce SO2 or O2, left
7. Reaction: 2SO2(g) O2(g) 3 2SO3(g); SO2 added
remove SO3, right
8. Reaction: 2NCl3(g) 3 N2(g) 3Cl2(g); NCl3 added
remove N2 or Cl2, right
Study Guide for Content Mastery Chemistry: Matter and Change • Chapter 18 105
Name Date Class
CHAPTER 18 STUDY GUIDE FOR CONTENT MASTERY
Section 18.2 continued
In your textbook, read about factors affecting chemical equilibrium.
Use each of the terms below just once to complete the passage.
right exothermic increase stress catalyst energy
smallest change reverse constant forward
increase
When you decrease the volume of a reaction vessel, you (9)
the pressure. This causes a reaction at equilibrium to shift to the side with the
(10) smallest number of moles. If the reaction has an equal number of
moles of reactants and products, changing the volume of the reaction vessel causes no
change
(11) in the equilibrium.
Changing the temperature of a reaction at equilibrium alters both the equilibrium
constant
(12) and the equilibrium position. When a reaction is
exothermic
(13) , which means it releases energy, lowering the temperature
right
shifts the equilibrium to the (14) because the forward reaction
stress
liberates heat and removes the (15) .
catalyst
A (16) speeds up a reaction by lowering the
Copyright © Glencoe/McGraw-Hill, a division of the McGraw-Hill Companies, Inc.
energy
(17) requirements for the reaction, but it does so equally in both the
forward
(18) and the (19) reverse directions. The reaction
will reach equilibrium more quickly, but with no change in the amount of product formed.
For each reaction below, indicate in which direction the equilibrium shifts when the
stated stress is applied to the system. Write R if the reaction shifts to the right, L if it
shifts to the left, or NC if there is no change.
Reaction Stress
L
20. PCl5(g) 3 PCl3(g) Cl2(g) heat temperature increase
NC
21. CO(g) Fe3O4(s) 3 CO2(g) 3FeO(s) volume increase
R 22. C2H2(g) H2O(g) 3 CH3CHO(g) heat temperature decrease
R
23. 2NO(g) H2(g) 3 N2O(g) H2O(g) heat volume decrease
L 24. Heat H2(g) I2(g) 3 2HI(g) temperature decrease
NC 25. H2(g) Cl2(g) 3 2HCl(g) heat volume decrease
106 Chemistry: Matter and Change • Chapter 18 Study Guide for Content Mastery
Name Date Class
CHAPTER 18 STUDY GUIDE FOR CONTENT MASTERY
Section 18.3 Using Equilibrium Constants
In your textbook, read about calculating equilibrium concentrations.
Answer the following questions.
1. What can you use the equilibrium constant to do?
Shift temperatire
2. Given the reaction: N2 O2 3 2NO for which the Keq at 2273 K is 1.2 104
a. Write the equilibrium constant expression for the reaction.
b. Write the equation that would allow you solve for the concentration of NO.
c. What is the concentration of NO if [N2] 0.166M and [O2] 0.145M?
3. What is the solubility product constant?
High
Copyright © Glencoe/McGraw-Hill, a division of the McGraw-Hill Companies, Inc.
4. What is the solubility product constant expression for the reaction:
Mg3(PO4)2(s) 3 3Mg2(aq) 2PO43(aq)
Low
5. Given the equilibrium BaSO4(s) 3 Ba2(aq) SO42(aq), what is the solubility
product constant expression?
High
6. The solubility product constant for BaSO4 at 298 K is 1.1 1010. Calculate the
solubility of BaSO4 in mol/L at 298 K.
Study Guide for Content Mastery Chemistry: Matter and Change • Chapter 18 107
Name Date Class
CHAPTER 18 STUDY GUIDE FOR CONTENT MASTERY
Section 18.3 continued
In your textbook, read about predicting precipitates.
The solubility product constant can be used to determine if a precipitate will form when
two aqueous solutions are mixed together. First, calculate the concentrations of the ions
in the final solution. Use the solubility product constant expression to calculate the ion
product (Qsp ) for the substance that might precipitate. Compare the result with the Ksp
of the substance.
7. What can you say about a solution when
a. Qsp is greater than Ksp?
b. Qsp is equal to Ksp?
c. Qsp is less than Ksp?
8. Predict whether a precipitate of AgBr will form if 100 mL of 0.0025M AgNO3 and
100 mL of 0.0020M NaBr are mixed.
Copyright © Glencoe/McGraw-Hill, a division of the McGraw-Hill Companies, Inc.
9. Explain briefly why Ag3PO4 might be more soluble in water than in the same volume of
a solution containing Na3PO4.
108 Chemistry: Matter and Change • Chapter 18 Study Guide for Content Mastery
