1. Factors That Affect Equilibrium

2. Le Châtelier’s Principle
If an external stress is applied to a system at equilibrium, the system adjusts in such a way that the stress is partially offset as the system reaches a new equilibrium position.
Stress: (disturbance)
Change in concentration
Increase/decrease solutes
Increase solvent (dilute)
Change in temperature
Increase/decrease (add or remove heat)
Change in volume/pressure (gases only)
Increase pressure (decrease volume)
Decrease pressure (increase volume)
Catalyst

4. Change in Concentration
N2 (g) + 3H2 (g) NH3 (g)

5. Example 1
PCl5(g) ⇆ PCl3(g) + Cl2(g) ΔH=-47kJ

6. Change in Pressure/Volume
N2O4 (g)
2NO2 (g)
Increase pressure
Decrease volume
Initial equilibrium
Final equilibrium

7. Example 2
PCl5(g) ⇆ PCl3(g) + Cl2(g)

8. Catalyst lowers Ea for both forward and reverse reactions.
Adding a Catalyst
does not change K
does not shift the position of an equilibrium system
system will reach equilibrium sooner
Catalyst lowers Ea for both forward and reverse reactions.
Catalyst does not change equilibrium constant or shift equilibrium.