1. Reaction Rates and Le Chatelier’s Principle

2. Rate of Reaction The rate of a chemical reaction
Describes how rapidly a chemical change takes place
They are determined by measuring changes in physical properties
Volume, Temperature, Color, Mass, or pH

3. Five Factors that Affect Reaction Rate
1. Nature of the reactants
2. Temperature
3. Concentration
4. Surface Area
5. Catalysts

4. Chemical Equilibrium
At equilibrium the forward reaction and the reverse reaction happen at the same time
There is no change in the amount of any substance in the reaction
Le Chatelier’s principle can be used to predict the effect of a change in conditions on a chemical equilibrium

5. Le Chatelier’s Principle Summarized
If a chemical system at equilibrium experiences a change (also called a stress) in concentration, temperature, volume, or total pressure; the equilibrium will shift in order to minimize that change.

6. See Saw A B C

7. Add More B A B B C
Which way does the see saw have to shift to reach equilibrium again?

8. The Shift A B B C
Which way does the see saw have to shift to reach equilibrium again?

9. Results A C SHIFT LEFT B B
More A is produced due to the shift in equilibrium

10. Synthesis of Ammonia H2 H2
NH3
NH3 N2 H2
N2 (g) + 3H2 (g)  2NH3 (g)

11. SHIFT will occur to side with the least number of MOLES
Increase Pressure
SHIFT RIGHT H2
NH3
NH3 H2 H2 N2
SHIFT will occur to side with the least number of MOLES
N2 (g) + 3H2 (g)  2NH3 (g)

12. Decreasing Volume (Think about how P and V relate with Boyle’s Law)
NH3
NH3 N2 H2
N2 (g) + 3H2 (g)  2NH3 (g)

13. SHIFT will occur to side with the least number of MOLES
Decrease Volume
SHIFT RIGHT H2
NH3
NH3 H2 H2 N2
SHIFT will occur to side with the least number of MOLES
N2 (g) + 3H2 (g)  2NH3 (g)

14. P and V
P and V are inversely related. That means as P increases, then V decreases.
The rule is when P increases or V decreases then the equilibrium will shift to the side with the least number of moles.
This only works if all of the components are gasses.

15. Decrease Volume = Increase Pressure
SHIFT RIGHT H2
NH3
NH3 H2 H2 N2
SHIFT will occur to side with the least number of MOLES
N2 (g) + 3H2 (g)  2NH3 (g)

16. Change in Temperature
Depends if reaction is Endothermic or Exothermic.
Endothermic: Heat on LEFT (+)
Exothermic: Heat on RIGHT (-)

17. Endothermic Increase Temperature… which way will the see saw tip? D A
HEAT D A C B

18. Which way will the reaction SHIFT?
Endothermic
Which way will the reaction SHIFT?
HEAT D C B A

19. Reaction will SHIFT Right
Endothermic
Reaction will SHIFT Right
HEAT D C B A

20. Endothermic Decrease Temperature… which way will the see saw tip? D A
HEAT D A C B

21. Which way will the reaction SHIFT?
Endothermic
HEAT
Which way will the reaction SHIFT? A B C D

22. Reaction will SHIFT Left
Endothermic
HEAT
Reaction will SHIFT Left A B C D

23. Exothermic Increase Temperature… which way will the see saw tip? D A C
HEAT D A C B

24. Which way will the reaction shift?
Exothermic A
HEAT B C D
Which way will the reaction shift?

25. Reaction will SHIFT LEFT
Exothermic A
HEAT B C D
Reaction will SHIFT LEFT

26. Exothermic DecreaseTemperature… which way will the see saw tip? D A C
HEAT D A C B
DecreaseTemperature… which way will the see saw tip?

27. Which way will the reaction shift?
Exothermic
HEAT D C B A
Which way will the reaction shift?

28. Reaction will SHIFT Right
Exothermic
HEAT D C B A
Reaction will SHIFT Right

29. 2H2O  2H2 + O2 Cause Effect Increase Reactant Concentration
How does each situation affect the chemical reaction?
2H2O  2H2 + O2
Cause Effect
Increase Reactant Concentration
Increase Product Concentration
Increase temperature of an endothermic reaction
Increase temperature of an exothermic reaction
Increase Pressure

30. Which INCREASE Reaction Rates?
Increasing Temperature
Increasing Concentration
Increasing Surface Area
Adding a Catalyst.
How are these factors related to Reaction Rates?
DIRECTLY

31. Nature of Reactants
Reaction rates are affected by the complexity of the bonds that must be broken and formed in the chemical reaction
The state of a reactant can also affect the reaction rate
Gases have the fastest and solids the slowest reaction rats
Because the frequency at which particles collide and the amount of energy they possess increase with increasing motion.

32. Continued
The faster particles are moving, the more frequent they will collide
Collide with greater kinetic energy.
Because of this TEMPERATURE and REACTION RATE are directly related