1. Le Châtelier’s Principle
If a change is imposed on a system at equilibrium, the position of the equilibrium will shift in a direction that tends to reduce that change
If a component (reactant or product) is added to a reaction system at equilibrium (constant T and P or constant T and V), the equilibrium position will shift in the direction that lowers the concentration of that component. If a component is removed, the opposite effect occurs.

2. As4O6(s) + 6C(s) <-> As4(g) + 6CO(g)
Example
As4O6(s) + 6C(s) <-> As4(g) + 6CO(g)
Predict the direction of the shift of the equilibrium position in response to each of the following changes in conditions:
Addition of carbon monoxide
Addition or removal of carbon or tetraarsenic hexoxide (As4O6)
Removal of gaseous arsenic (As4)

3. Changing Pressure Add or remove a gaseous reactant or product
Add an inert gas (one not involved in the reaction) - won’t affect equilibrium
Change the volume of the container**

4. N2(g) + 3H2(g) <-> 2NH3(g)
Changing Volume
When the volume of a container changes, the system also must change its volume (by changing the number of molecules present)
Products/Reactants will decrease/increase based on what will have the larger affect (how many molecules are present)
N2(g) + 3H2(g) <-> 2NH3(g)
Decreasing volume -> shifts right
Increasing volume -> shifts left

5. Example If the volume is reduced, what will happen to the equilibrium?
P4(s) + 6Cl2(g) <-> 4PCl3(l)
Answer: Shifts RIGHT
PCl3(g) + Cl2(g) <-> PCl5(g)
PCl3(g) + 3NH3(g) <-> P(NH2)3(g) + 3HCl(g)
Answer: No Shift

6. Changing Temperature This will affect the equilibrium constant (K)
Depending on whether the reaction is endothermic (heat is a reactant) or exothermic (heat is a product) will determine which way the reaction shifts
N2(g) + 3H2(g) <-> 2NH3(g) + 92kJ
Energy Added (increase temp) = Eq shift L, K decreases
556kJ + CaCO3(s) <-> CaO(s) + CO2(g)
Energy Added (increase temp) = Eq shift R, K increases

7. Predict how K will change as temperature is increased:
Example
Predict how K will change as temperature is increased:
N2(g) + O2(g) <-> 2NO(g) ∆H° = 181kJ
Answer: shifts right, K increases
b. 2SO2(g) + O2(g) <-> 2SO3(g) ∆H° = -198kJ
Answer: shifts left, K decreases

8. Summary - Know Concepts For Test
58 kJ + N2O4(g) <-> 2NO2(g)
CHANGE
SHIFT
Add N2O4(g)
Right
Add NO2(g)
Left
Remove N2O4(g)
Remove NO2(g)
Add He(g)
None
Decrease Container Volume
Increase Container Volume
Increase Temperature
Decrease Temperature