1. N2O4(g) + energy  2 NO2(g) (colourless) (reddish-brown)

2. Le Chatelier’s Principle
When a chemical system at equilibrium is disturbed by a stress, the system adjusts (shifts) to oppose the change
Stresses include:
Change in concentration
Change in pressure (or volume)
Change in temperature

3. Change in Concentration
A(g) + 3B(g)  2C(g) + heat
Increasing the concentration of the reactants OR
Decreasing the concentration of the products
Will favour the forward reaction, causing the equilibrium to shift to the RIGHT
Decreasing the concentration of the reactants OR
Increasing the concentration of the products
Will favour the reverse reaction, causing the equilibrium to shift to the LEFT
RECALL: Addition or removal of solid or liquids does not change the concentration. Therefore does not cause a shift. I.e. only applies to gases and aqueous solutions.

4. Change in Concentration

5. N2(g) + 3H2(g)  2NH3

6. Change in Pressure A(g) + 3B(g)  2C(g) + heat
 volume  pressure
 volume  pressure
A(g) + 3B(g)  2C(g) + heat
Increasing the volume of the container OR
Decreasing the pressure
Will cause a shift to the side with MORE gas molecules
In our example, it will shift left (4 molreactants > 2 molproducts)
Decreasing the volume of the container OR
Increasing the pressure
Will cause a shift to the side with LESS gas molecules
In our example, it will shift right (4 molreactants > 2 molproducts)

8. Change in Temperature In an exothermic reaction:
Increasing the temperature will cause a shift to the LEFT
Decreasing the temperature will cause a shift to the RIGHT

9. Change in Temperature In an endothermic reaction:
Increasing the temperature will cause a shift to the RIGHT
Decreasing the temperature will cause a shift to the LEFT

10. Change in Temperature
Recall: Keq is temperature dependent. Therefore, changes in temperature will also affect Keq
Shift right =  products,  Keq
Shift left =  reactants, Keq

11. Variables that do NOT Affect Equilibrium
Catalysts
Increases reaction rate by lowering activation energy (of BOTH the forward and the reverse reactions equally)
Decreases the time required to reach equilibrium but does not affect the final position of equilibrium
Inert Gases
Increases the pressure, which will increase reaction rate
Increases the probability of successful collisions for BOTH products and reactants equally

12. Practice!
Read p
P. 457 #1-6
P. 459 #1-6