1. Equilibrium

2. Can You…. Define Le Chatelier’s Principle?
Describe the three ways to change the equilibrium in a system?
Predict which direction a reaction will proceed when a stress is applied to a system?

3. What is Equilibrium Reversible Reactions
Products can react to re-form the reactants
Shown with a double arrow
Chemical Equilibrium
When the rate of the forward equals the rate of the reverse

4. What is “K” or the Equilibrium Constant?
What is Equilibrium
What is “K” or the Equilibrium Constant?
Less than 1
more reactants present
Equilibrium lies to the left
Reactant favored
Equal to 1
equal amount of product and reactant
Neither products or reactants favored
Greater than 1 = more products present
More products present
Equilibrium lies to the right
Product favored

5. What is Equilibrium A Sample Problem
Given the data below, calculate the value for the equilibrium constant.
2 NO (g) + Cl2(g) ⇌ 2 NOCl (g)
At equilibrium [NO (g)] = 1.20 M
[Cl2(g)] = 0.75 M
[NOCl (g)] = 0.88 M

6. Le Chatelier’s Principle
If a system is stressed, the equilibrium will shift to relieve the stress
Three Methods to Stress A System
Add/Remove a substance
Change the temperature
Change the pressure
LEARN BY DOING!!!!!

7. Change the Pressure Increase pressure = go to side with less gas
Decrease the pressure = go to side with more gas
2 NO2(g)  N2O4(g)
Increase the pressure =
Decrease the pressure =

8. Change the Temperature
Endothermic Reactions
Energy as reactant
Uses energy
Units of energy = kJ = kilojoules
Feels cold to the touch
Exothermic Reactions
Energy as product
Produces energy
Feels warm to the touch

9. Change the Temperature
Increase temperature – shift away from heat
Decrease temperature – shift towards heat
556kJ CaCO3 (s)  CaO (s) CO2 (g)
Type of Reaction
Increase temperature
Decrease Temperature

10. Change the Concentration
If you add, shift away from what you add
If you remove, shift towards to remake
Adding solids or liquids does not change equilibrium
Example
345kJ NH4Cl (s) ↔ NH3 (g) HCl(g)
Add NH4Cl
Add NH3   
Remove HCl
Add Heat