1. Chapter 17 “Reaction Rates and Equilibrium” Part 2: Equilibrium
Reactants ⇌ Products
Equilibrium #4.ppt
Equilibrium #4.ppt

2. Today you will learn… What factors affect chemical equilibrium
How to predict the effects of changing conditions in an equilibrium system according to Le Chatelier’s Principle

3. Le Chatelier’s Principle
The French chemist Henri Le Chatelier ( ) studied how the equilibrium position shifts as a result of changing conditions
Le Chatelier’s principle: If stress is applied to a system in equilibrium, the system changes in a way that relieves the stress

4. Le Chatelier’s Principle
What items did he consider to be stress on the equilibrium?
Concentration
Temperature
Pressure
Each of these will now be discussed in detail

5. Le Chatelier’s Principle
Concentration – adding more reactant produces more product, and removing the product as it forms will produce more product
(See-saw demo)

6. Le Chatelier’s Principle
Temperature – increasing the temperature causes the equilibrium position to shift in the direction that absorbs heat
If exothermic, heat is on the products side
Cooling an exothermic reaction will take away product
This favors products
Example: C + O2(g) ⇌ CO2(g) H = kJ

7. Le Chatelier’s Principle
Temperature – increasing the temperature causes the equilibrium position to shift in the direction that absorbs heat
If exothermic, heat is on the products side
Increasing temperature adds product
This would shift the reaction to the reactant side
Example: C + O2(g) ⇌ CO2(g) H = kJ

8. Le Chatelier’s Principle
Pressure – changes in pressure will only effect gaseous equilibria
P is on the side with more moles of gas
N2(g) + 3H2(g) ⇌ 2NH3(g)
For every two molecules of ammonia made, four molecules of reactant are used up – P is on the left side
Increase P means…
shifts to the right

9. Le Châtelier’s Principle
Adding a Catalyst
does not change K
does not shift the position of an equilibrium system
system will reach equilibrium sooner
uncatalyzed
catalyzed
Catalyst lowers Ea for both forward and reverse reactions.
Catalyst does not change equilibrium constant or shift equilibrium.

10. Le Chatelier’s Principle