Name ________________________________________
Date _________________
Class ___________________________
17
Chemical Equilibrium
Section 17.1
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 _____________________.
2. A reaction that can occur in both the forward and the reverse directions is called a(n)
_____________________.
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 ___________________ but that
does not mean that the amounts or concentrations are ___________________.
5. Equilibrium is a state of _____________________, not one of _____________________.
In your textbook, read about equilibrium expressions and constants.
For each statement below, write true or false.
__________________
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.
__________________
7.
The equation H2(g)  I2(g)  2HI(g) is an example of a homogeneous equilibrium.
__________________
8.
If an equilibrium constant has a value less than one, the reactants are favored at
equilibrium.
__________________
9.
The value for Keq is constant only at a specific volume.
__________________ 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.
__________________ 11.
A heterogeneous equilibrium means that reactants and products are present in more
than one state.
__________________ 12.
The product of the forward chemical reaction is HI, for the equilibrium expression:
K eq 
Chemistry: Matter and Change
[HI]2
[H 2 ][I2 ]
1
Study Guide
Name ________________________________________
Date _________________
Class ___________________________
13
17
Section 17.1 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)  2SO3(g) at 873 K
Experiment 1
Initial concentrations
Equilibrium concentrations
Experiment 2
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.
______________________________________________________________________________________________
14. Is this reaction an example of a homogeneous or heterogeneous equilibrium?
______________________________________________________________________________________________
15. Calculate the equilibrium constant from the data obtained in experiment 1.
______________________________________________________________________________________________
______________________________________________________________________________________________
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?
______________________________________________________________________________________________
______________________________________________________________________________________________
18. What does this experiment show about the initial concentrations of products and
reactants in a reversible reaction?
______________________________________________________________________________________________
______________________________________________________________________________________________
______________________________________________________________________________________________
Chemistry: Matter and Change
2
Study Guide
Name ________________________________________
Date _________________
Class ___________________________
13
17
Section 17.2
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?
______________________________________________________________________________________________
______________________________________________________________________________________________
2. What are three kinds of stresses that can be placed on a system?
______________________________________________________________________________________________
______________________________________________________________________________________________
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)  2NH3(g); NH3 added
______________________________________________________________________________________________
4. Reaction: H2(g)  I2(g)  2HI(g); H2 added
______________________________________________________________________________________________
5. Reaction: CO(g)  H2O  CO2(g)  H2(g); H2O added
______________________________________________________________________________________________
6. Reaction: 2SO2(g)  O2(g)  2SO3(g); SO3 added
______________________________________________________________________________________________
7. Reaction: 2SO2(g)  O2(g)  2SO3(g); SO2 added
______________________________________________________________________________________________
8. Reaction: 2NCl3(g)  N2(g)  3Cl2(g); NCl3 added
______________________________________________________________________________________________
Chemistry: Matter and Change
3
Study Guide
Name ________________________________________
Date _________________
Class ___________________________
13
17
Section 17.2 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
smallest
change
reverse
constant
forward
energy
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) ________________________ 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
(11) ________________________ in the equilibrium.
Changing the temperature of a reaction at equilibrium alters both the equilibrium
(12) ________________________ and the equilibrium position. When a reaction is
(13) ________________________, which means it releases energy, lowering the temperature shifts the
equilibrium to the (14) ________________________ because the forward reaction liberates heat and
removes the (15) ________________________.
A (16) ________________________ speeds up a reaction by lowering the
(17) ____________________ requirements for the reaction, but it does so equally in both the
(18) _____________________ and the (19) _____________________ 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
_________ 20. PCl5(g)  PCl3(g)  Cl2(g)  heat
temperature increase
_________ 21. CO(g)  Fe3O4(s)  CO2(g)  3FeO(s)
volume increase
_________ 22. C2H2(g)  H2O(g)  CH3CHO(g)  heat
temperature decrease
_________ 23. 2NO(g)  H2(g)  N2O(g)  H2O(g)  heat
volume decrease
_________ 24. Heat  H2(g)  I2(g)  2HI(g)
temperature decrease
_________ 25. H2(g)  Cl2(g)  2HCl(g)  heat
volume decrease
Chemistry: Matter and Change
4
Study Guide
Name ________________________________________
Date _________________
Class ___________________________
13
17
Section 17.3
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?
______________________________________________________________________________________________
______________________________________________________________________________________________
2. Given the reaction: N2  O2  2NO for which the Keq at 2273 K is 1.2104
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?
______________________________________________________________________________________________
______________________________________________________________________________________________
4. What is the solubility product constant expression for the reaction:
Mg3(PO4)2(s)  3Mg2(aq)  2PO43(aq)
______________________________________________________________________________________________
5. Given the equilibrium BaSO4(s)  Ba2(aq)  SO42(aq), what is the solubility product constant
expression?
______________________________________________________________________________________________
6. The solubility product constant for BaSO4 at 298 K is 1.11010. Calculate the
solubility of BaSO4 in mol/L at 298 K.
______________________________________________________________________________________________
______________________________________________________________________________________________
______________________________________________________________________________________________
______________________________________________________________________________________________
Chemistry: Matter and Change
5
Study Guide
Name ________________________________________
Date _________________
Class ___________________________
13
17
Section 17.3 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.
______________________________________________________________________________________________
______________________________________________________________________________________________
______________________________________________________________________________________________
______________________________________________________________________________________________
______________________________________________________________________________________________
9. Explain briefly why Ag3PO4 might be more soluble in water than in the same volume of a solution
containing Na3PO4.
______________________________________________________________________________________________
______________________________________________________________________________________________
______________________________________________________________________________________________
______________________________________________________________________________________________
______________________________________________________________________________________________
Chemistry: Matter and Change
6
Study Guide
TEACHER GUIDE AND ANSWERS
Study Guide - Chapter 17 – Chemical
Equilibrium
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
Section 17.1 Equilibrium: A State of Dynamic
Balance
1. completion
2. reversible reaction
3. Chemical equilibrium
4. constant, equal
5. action, inaction
6. false
7. true
8. true
9. false
10. false
11. true
12. true
13. Keq  [SO3]2/[SO2]2[O2]
14. homogeneous
15. Keq  4.32
Section 17.3 Using Equilibrium Constants
1. The equilibrium constant is used to calculate the
equilibrium concentration of a substance if the
concentrations of all other reactants and products are
known.
2. a. Keq  [NO]2/[N2][O2]
Solution: [3.50]2/[1.50]2[1.26]  4.32098  4.32
16. Keq  4.32
Solution: [0.260]2/[0.590]2[0.0450]
 4.31549  4.32
17. No; because both experiments were done at the
same temperature, the equilibrium constant would
be the same.
18. This experiment shows that it does not matter what
the initial concentrations of products and reactants are
in a reversible reaction. When the reaction is at
equilibrium, they will have the same ratio to one
another.
b. [NO]2  Keq [N2][O2]
c. 1.7 10–3M
Solution: [NO2  (1.2×10–4) (0.166M) 
(0.145M)  2.888410–6M
Taking the square root gives 1.699510–3, which
rounds to  1.710–3M
3. The solubility product constant is an equilibrium
constant for the dissolving of a sparingly soluble ionic
compound in water.
4. Ksp  [Mg2]3[PO43–]2
5. Ksp  [Ba2][SO42–]
Section 17.2 Factors Affecting Chemical
Equilibrium
1. If a stress is applied to a system at equilibrium, the
system shifts in the direction that relieves the stress.
2. Answers may vary, but should include changes in
concentration, volume, and temperature. Some
students may list pressure in place of volume.
3. left; remove N2 or H2
4. right; add I2 or remove HI
5. right; add CO or remove CO2 or H2
6. left; remove SO2 or O2
7. right; remove SO3
Chemistry: Matter and Change
right; remove N2 or Cl2
increase
smallest
change
constant
exothermic
right
stress
catalyst
energy
forward
reverse
L
NC
R
R
L
NC
6. Ksp  [Ba2][SO42–]  1.110–10
[Ba2][SO42]  (s)(s)  s2  1.110–10
7
Teacher Guide and Answers
TEACHER GUIDE AND ANSWERS
8. AgBr(s)  Ag (aq)  Br–(aq)
Qsp  [Ag]/2 [Br–]/2
Qsp  (0.00125)(0.0010)  1.310–6

s  1.1  1010 s2  1.110-5 mol/L
The solubility of BaSO4 is 1.010–5 mol/L
at 298 K.
7. a. This indicates that a precipitate will form. The
precipitate will reduce the ion concentrations
in the solution until the Ksp expression is
satisfied.
b. This indicates that the solution is saturated so no
further change will occur.
c. This indicates that the solution is unsaturated and
no precipitate will form.
Chemistry: Matter and Change
Qsp (1.310–6) > Ksp (5.410–13
A precipitate will form.
9. Not as much Ag3PO4 would dissolve in a Na3PO4
solution because of the common ion effect. The
substances have PO43– ions in common. Because of
the high concentration of PO43– ions, only a small
concentration of Ag can be present in the
equilibrium mixture. The solubility of Ag3PO4 is
equal to the Ag ion concentration.
8
Teacher Guide and Answers