1. Equilibrium Systems and Stress
Page 512 in Text
Page 7:11 in Regents Review Book

2. Phase Equilibrium
Phase Equilibrium
Liquid/Gas Equilibrium

3. Phase Equilibrium Liquid to Gas:
When water vapor evaporates at the same rate it condenses in a closed container, dynamic equilibrium
exists

4. Phase Equilibrium Phase Equilibrium Solid/Liquid Equilibrium
Liquid/Gas Equilibrium
Solid/Liquid Equilibrium

5. Phase Equilibrium Melting/Freezing Equilibrium
Occurs when the rate of solid to liquid equals the rate of liquid to solid

6. Phase Equilibrium Solution Equilibrium Occurs in a saturated solution
The rate of ions or molecules dissolving in the liquid equals the rate of ions/molecules recrystallizing on the bottom of the beaker

7. Phase Equilibrium
Solution Equilibrium

8. Phase Equilibrium Gas in a Liquid
Occurs when the rate that a gas dissolves in a liquid equals the rate that a gas comes out of a liquid
Greatly affected by temperature and pressure

9. Chemical Equilibrium Chemical Equilibrium 2CO(g) + O2(g) ↔ 2O2(g)
When the rates of the forward and reverse reactions are equal in a chemical reaction
The concentration (amount) of reactants and products of the reaction remains the same
Ex:
2CO(g) + O2(g) ↔ 2O2(g)

10. Chemical Equilibrium

11. Le Chatlelier’s Principle
Stress: something that causes a change in a system at equilibrium
However, the system will adjust to this new stress and come back into equilibrium again
This is LE CHATLELIER’S PRINCIPLE

12. Le Chatelier’s Principle
This is LE CHATELIER’S PRINCIPLE
When a system at equilibrium is disturbed, the system adjusts in a way to reduce the change

13. Le Chatelier’s Principle
Chemical equilibria responds to three kinds of stress:
Changes in the concentration of reactants or products
Changes in temperature
Changes in pressure

14. Le Chatelier’s Principle
1. Changes in concentration of reactants and products
This is a model of the system at equilibrium.

15. Changes in concentration of reactants and products
If more reactants are added to the system, the equilibrium changes. The system will respond by making more product.
Stress is being added to the system here

16. Changes in concentration of reactants and products
1 CO(g) + 2H2(g) ↔ CH3OH(g)
System at equilibrium:
System with added reactant CO:
To reach equilibrium again, the system will make more products:
The reaction will shift to the right (the forward reaction)

17. Changes in concentration of reactants and products
1 CO(g) + 2H2(g) ↔ CH3OH(g)
System at equilibrium:
System with added product (CH3OH)
To reach equilibrium, the system will make more reactants
The reaction will shift to the left (reverse reaction)

18. Effects of Temperature
Temperature effects equilibrium the same way as concentration changes
For exothermic forward reactions:
Increasing the temperature of an equilibrium system usually leads to a shift in favor of the reactants
For endothermic forward reactions:
Increasing the temperature usually leads to a shift in favor of the products

19. Effects of Temperature
N2(g) O2(g) ↔ 2NO(g)
System at Equilibrium
System with added heat on the product side
To reach equilibrium, the system will make more reactants
The reaction favors the formation of reactants (reverse rxn)

20. Effects of Pressure
For solutions, pressure has almost no effect on the equilibrium
Gases are greatly effected by changes in pressure
An increase in pressure causes the system to shift its equilibrium position to REDUCE THE PRESSURE
To reduce pressure, the system needs to reduce the number of gas particles

21. Effect of Pressure
Rule: At constant temperature, increasing the pressure on a gas causes the system to shift in the direction that reduces the number of moles of gas.
go.hrw.com

22. Effects of Pressure Example: N2O4(g) ↔ 2NO2(g)
How many moles of gas are on the reactant side?_____
How many moles of gas are on the product side?_____
Which side has the greater amount of moles?________
If adding pressure to this system causes the system to respond by reducing the number of moles of gas, which way will the reaction go?

23. Real Life Applications
The “Bends”
Nitrogen and other gases are dissolved in our blood
nitrogen(g) ↔ nitrogen(dissolved)
As the diver comes up from the high pressures of the ocean, the equilibrium shifts to the left
If they come up too fast, nitrogen bubbles form in the blood and other body fluids cause severe abdominal pain and maybe death