1. Le Chatelier’s Principle

2. Disrupting Equilibrium Equilibrium can be disrupted by: changing concentrations of reactants and/or products changing the temperature changing the pressure (gaseous reactions) When equilibrium is disrupted, the rate of the forward rxn no longer equals the rate of the reverse rxn

3. Le Chatelier’s Principle a way of predicting what happens to the relative rates of the forward and reverse reactions when equilibrium is disrupted The Law: when a system at equilibrium is upset, the system responds by changing in a way which counteracts ( undoes) the disturbance eventually equilibrium is restored

4. Changing Concentration Type of ChangeResponse increase shifts to consume (use up) the added reactant or product decreaseshifts to replace (produce) the removed reactant or product

5. Changing Temperature Type of ChangeResponse increase shifts to favour the endothermic change decreaseshifts to favour the exothermic change

6. Changing Volume NOTE: only impacts reactions involving gases Type of ChangeResponse increase (decrease in pressure) shifts towards the side with the greater number of moles of gas decrease (increase in pressure)shifts towards the side with the fewest number of moles of gas

7. Adding a Catalyst Type of ChangeResponse No effect but equilibrium is established faster

8. Adding an Inert Gas Type of ChangeResponse No effect.

9. Examples 1) N 2 O 4 (g)  2 NO 2 (g) ΔH = + 24kJ/mol colourless brown UpsetObservationDirection of Shift T  T  V  V 

10. Examples 1) N 2 O 4 (g)  2 NO 2 (g) ΔH = + 24kJ/mol colourless brown UpsetObservationDirection of Shift T  Darker brown  T  V  V 

11. Example 1) N 2 O 4 (g)  2 NO 2 (g) ΔH = + 24kJ/mol colourless brown UpsetObservationDirection of Shift T  Darker brown  T  Lighter brown  V  V 

12. Examples 1) N 2 O 4 (g)  2 NO 2 (g) ΔH = + 24kJ/mol colourless brown UpsetObservationDirection of Shift T  Darker brown  T  Lighter brown  V  Darker brown  V 

13. Examples 1) N 2 O 4 (g)  2 NO 2 (g) ΔH = + 24kJ/mol colourless brown UpsetObservationDirection of Shift T  Darker brown  T  lighter brown  V  Darker brown  V  Lighter brown 

14. Examples 1) N 2 O 4 (g)  2 NO 2 (g) ΔH = + 24kJ/mol colourless brown UpsetObservationDirection of Shift T  Darker brown  T  lighter brown  V  Darker brown  V  Lighter brown 

15. Showing LCP Graphically Initial equilibrium T  rate of forward greater than rate of reverse new equilibrium

16. Impact of Temperature on K Ex. From the previous graph, calculate K for the initial equilibrium and for the new equilibrium. On board

17. Impact of Temperature on K Type of Rxn in Forward Direction TemperatureValue for K Endothermic  Increases Exothermic  Decreases Endothermic  Decreases Exothermic  Increases

18. Example [Co(H 2 O) 6 ] 2+ (aq) + 4Cl - (aq)  CoCl 4 2- (aq) + 6 H 2 O (l) Pink Blue UpsetObservationDirection of Shift Add conc. HCl TT TT Add H 2 O

19. Example [Co(H 2 O) 6 2+ (aq) + 4Cl - (aq)  CoCl 4 2- (aq) + 6 H 2 O (l) Pink Blue UpsetObservationDirection of Shift Add conc. HClblue  TT TT Add H 2 O

20. Example [Co(H 2 O) 6 2+ (aq) + 4Cl - (aq)  CoCl 4 2- (aq) + 6 H 2 O (l) Pink Blue UpsetObservationDirection of Shift Add conc. HClblue  TT  TT Add H 2 O

21. Example [Co(H 2 O) 6 2+ (aq) + 4Cl - (aq)  CoCl 4 2- (aq) + 6 H 2 O (l) Pink Blue UpsetObservationDirection of Shift Add conc. HClblue  TT  TT pink  Add H 2 O

22. Example [Co(H 2 O) 6 2+ (aq) + 4Cl - (aq)  CoCl 4 2- (aq) + 6 H 2 O (l) Pink Blue Based on the observations, is the forward rxn endo or exothermic? UpsetObservationDirection of Shift Add conc. HClblue  TT  TT pink  Add H 2 Opink 

23. Example [Co(H 2 O) 6 2+ (aq) + 4Cl - (aq)  CoCl 4 2- (aq) + 6 H 2 O (l) Pink Blue Based on the observations, is the forward rxn endo or exothermic? ENDO UpsetObservationDirection of Shift Add conc. HClblue  TT  TT pink  Add H 2 Opink 