1. Chapter AP Chem
Chemical Equilibrium

2. 13.1 The Equilibrium Condition 13.2 The Equilibrium Constant
Chapter 13
Table of Contents
13.1 The Equilibrium Condition
13.2 The Equilibrium Constant
13.3 Equilibrium Expressions Involving Pressures
13.4 Heterogeneous Equilibria
13.5 Applications of the Equilibrium Constant
13.6 Solving Equilibrium Problems
13.7 Le Châtelier’s Principle
Copyright © Cengage Learning. All rights reserved

3. *Be sure all reports are turned in and made up TODAY!
Chapter 13
Table of Contents
WEEK OUTLOOK
Monday - Notes with problems w/sheet due Tuesday - should be able to complete in class today.
*Be sure all reports are turned in and made up TODAY!
Tuesday - Notes with emphasis on Le Chatelier’s Principle emphasized & problems assigned due Wed. - some time in class to complete
Kaci & Jonathan - library 2nd floor 7:30 with ACT invent.
Wednesday- Lab
Thursday - CAPS - No class
Friday - Good Friday - No school
Tuesday - April 2nd - ACT Testing 11th graders only.
Test probably next Thursday - just over ch. 13 only.
Copyright © Cengage Learning. All rights reserved 3

4. HANDOUT - Equilibrium Homework Sheet #1
Chapter 13
Table of Contents
HANDOUTS - Ch. 13 NMSI Equilibrium Packet (Notes with practice problems)
HANDOUT - Equilibrium Homework Sheet #1
TURN IN Kinetics Lab - will go over pre-lab questions
HW: Equilibrium w/s #1 should be done today - due Mon. for grade
HW: Notes packet #1-6 problems due next week but keep for studying.
CW: Notes
VOTE ON KINETICS TESTING CH. 12
Iodine Clock Rxn. Simulation Lab - as time permits
Copyright © Cengage Learning. All rights reserved

5. Dynamic Nature of Equilibrium
When a system reaches equilibrium, the forward and reverse reactions continue to occur … but at equal rates.
We are usually concerned with the situation after equilibrium is reached.
After equilibrium the concentrations of reactants and products remain constant.
Prentice Hall © 2005
Chapter Fourteen
General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry

6. Section 13.1
The Equilibrium Condition
Chemical Equilibrium
The state where the concentrations of all reactants and products remain constant with time.
On the molecular level, there is frantic activity. Equilibrium is not static, but is a highly dynamic situation.
Return to TOC
Copyright © Cengage Learning. All rights reserved

7. Macroscopically static Microscopically dynamic
Section 13.1
The Equilibrium Condition
Equilibrium Is:
Macroscopically static 
Microscopically dynamic
Return to TOC
Copyright © Cengage Learning. All rights reserved

8. Changes in Concentration
Section 13.1
The Equilibrium Condition
Changes in Concentration
N2(g) + 3H2(g) NH3(g)
Return to TOC
Copyright © Cengage Learning. All rights reserved

9. Section 13.1
The Equilibrium Condition
Chemical Equilibrium
Concentrations reach levels where the rate of the forward reaction equals the rate of the reverse reaction.
Return to TOC
Copyright © Cengage Learning. All rights reserved

10. The Changes with Time in the Rates of Forward and Reverse Reactions
Section 13.1
The Equilibrium Condition
The Changes with Time in the Rates of Forward and Reverse Reactions
Return to TOC
Copyright © Cengage Learning. All rights reserved

11. H2O(g) + CO(g) H2(g) + CO2(g)
Section 13.1
The Equilibrium Condition
Concept Check
Consider an equilibrium mixture in a closed vessel reacting according to the equation:
H2O(g) + CO(g) H2(g) + CO2(g)
You add more H2O(g) to the flask. How does the concentration of each chemical compare to its original concentration after equilibrium is reestablished? Justify your answer.
The concentrations of each product will increase, the concentration of CO will decrease, and the concentration of water will be higher than the original equilibrium concentration, but lower than the initial total amount.
Students may have many different answers (hydrogen goes up, but carbon dioxide in unchanged, etc.) Let them talk about this for a while – do not go over the answer until each group of students has come up with an explanation. This question also sets up LeChâtelier’s principle for later.
Return to TOC
Copyright © Cengage Learning. All rights reserved

12. H2O(g) + CO(g) H2(g) + CO2(g)
Section 13.1
The Equilibrium Condition
Concept Check
Consider an equilibrium mixture in a closed vessel reacting according to the equation:
H2O(g) + CO(g) H2(g) + CO2(g)
You add more H2 to the flask. How does the concentration of each chemical compare to its original concentration after equilibrium is reestablished? Justify your answer.
This is the opposite scenario of the previous slide. The concentrations of water and CO will increase. The concentration of carbon dioxide decreases and the concentration of hydrogen will be higher than the original equilibrium concentration, but lower than the initial total amount.
Return to TOC
Copyright © Cengage Learning. All rights reserved

13. Consider the following reaction at equilibrium:
Section 13.2
Atomic Masses
The Equilibrium Constant
Law of Mass Action
Consider the following reaction at equilibrium:
jA + kB lC + mD
A, B, C, and D = chemical species.
Square brackets = concentrations of species at equilibrium.
j, k, l, and m = coefficients in the balanced equation.
K = equilibrium constant (given without units). l m
[C]
[D] K =
[A] j
[B] k
Return to TOC
Copyright © Cengage Learning. All rights reserved

14. Conclusions About the Equilibrium Expression
Section 13.2
The Equilibrium Constant
Atomic Masses
Conclusions About the Equilibrium Expression
Equilibrium expression for a reaction is the reciprocal of that for the reaction written in reverse.
When balanced equation for a reaction is multiplied by a factor of n, the equilibrium expression for the new reaction is the original expression raised to the nth power;
thus Knew = (Koriginal)n.
K values are usually written without units.
Return to TOC
Copyright © Cengage Learning. All rights reserved

15. Conclusions about Equilibrium Expressions
The equilibrium expression for a reaction is the reciprocal for a reaction written in reverse
2NO2(g)  2NO(g) + O2(g)
2NO(g) + O2(g) 2NO2(g)

16. Conclusions about Equilibrium Expressions
When the balanced equation for a reaction is multiplied by a factor n, the equilibrium expression for the new reaction is the original expression, raised to the nth power.
2NO2(g)  2NO(g) + O2(g)
NO2(g)  NO(g) + ½O2(g)

17. Equilibrium position is a set of equilibrium concentrations.
Section 13.2
Atomic Masses
The Equilibrium Constant
K always has the same value at a given temperature regardless of the amounts of reactants or products that are present initially.
For a reaction, at a given temperature, there are many equilibrium positions but only one value for K.
Equilibrium position is a set of equilibrium concentrations.
Return to TOC
Copyright © Cengage Learning. All rights reserved

18. K involves concentrations - (also called Kc)
Section 13.3
Equilibrium Expressions Involving Pressures
The Mole
K involves concentrations - (also called Kc)
Kp involves pressures for gases.
Return to TOC
Copyright © Cengage Learning. All rights reserved

19. N2(g) + 3H2(g) 2NH3(g) Equilibrium Expressions Involving Pressures
Section 13.3
Equilibrium Expressions Involving Pressures
The Mole
Example
N2(g) + 3H2(g) NH3(g)
Return to TOC
Copyright © Cengage Learning. All rights reserved

20. Equilibrium pressures at a certain temperature:
Section 13.3
Equilibrium Expressions Involving Pressures
The Mole
Example
N2(g) + 3H2(g) NH3(g)
Equilibrium pressures at a certain temperature:
Return to TOC
Copyright © Cengage Learning. All rights reserved

21. N2(g) + 3H2(g) 2NH3(g) Equilibrium Expressions Involving Pressures
Section 13.3
Equilibrium Expressions Involving Pressures
The Mole
Example
N2(g) + 3H2(g) NH3(g)
Return to TOC
Copyright © Cengage Learning. All rights reserved

22. The Relationship Between K and Kp
Section 13.3
Equilibrium Expressions Involving Pressures
The Mole
The Relationship Between K and Kp
Kp = K(RT)Δn
Δn = sum of the coefficients of the gaseous products minus the sum of the coefficients of the gaseous reactants.
R = L·atm/mol·K
T = temperature (in kelvin)
Return to TOC
Copyright © Cengage Learning. All rights reserved

23. Section 13.3
Equilibrium Expressions Involving Pressures
The Mole
Example
N2(g) + 3H2(g) NH3(g)
Using the value of Kp (3.9 × 104) from the previous example, calculate the value of K at 35°C.
Return to TOC
Copyright © Cengage Learning. All rights reserved

24. Homogeneous Equilibria
Section 13.4
Heterogeneous Equilibria
Homogeneous Equilibria
Homogeneous equilibria – involve the same phase:
N2(g) + 3H2(g) NH3(g)
HCN(aq) H+(aq) + CN-(aq)
Return to TOC
Copyright © Cengage Learning. All rights reserved

25. Heterogeneous Equilibria
Section 13.4
Heterogeneous Equilibria
Heterogeneous Equilibria
Heterogeneous equilibria – involve more than one phase:
2KClO3(s) KCl(s) + 3O2(g)
2H2O(l) H2(g) + O2(g)
Return to TOC
Copyright © Cengage Learning. All rights reserved

26. The concentrations of pure liquids and solids are constant.
Section 13.4
Heterogeneous Equilibria
The position of a heterogeneous equilibrium does not depend on the amounts of pure solids or liquids present.
The concentrations of pure liquids and solids are constant.
2KClO3(s) KCl(s) + 3O2(g)
Return to TOC
Copyright © Cengage Learning. All rights reserved

27. Equilibria Involving Pure Solids and Liquids
The equilibrium constant expression does not include terms for pure solid and liquid phases because their concentrations do not change in a reaction.
Although the amounts of pure solid and liquid phases change during a reaction, these phases remain pure and their concentrations do not change.
Example: CaCO3(s) CaO(s) + CO2(g)
[CaO] [CO2]
Kc = ––––––––––
[CaCO3]
Kc = [CO2]
Prentice Hall © 2005
Chapter Fourteen
General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry

28. Heterogeneous Equilibria
ASSIGNMENTS - 2/20/14
Section 13.4
Heterogeneous Equilibria
W/sheet #1 problems due Monday
This assignment should be able to be completed today in class but is due Monday.
Ch. 13 Equilibrium packet - #1-#6 practice problems - answers shown to see if you are doing correctly.
Prepare for Test on Kinetics.
HW: Read chapter 13 over the next week.
Ch. 12 Kinetics Test - VOTED for WEDNESDAY - Feb 26
Return to TOC
Copyright © Cengage Learning. All rights reserved