1. LeChâtelier

2. Equilibrium
An equilibrium is reached when the RATE of forward reaction equals the RATE of the reverse reaction
This does NOT mean that the concentrations are the same.
N2 + 3H2  2NH3
Reversible Reactions: The reactions occur simultaneously in both directions.

3. 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

4. LeChâtelier’s Principle
General rules
ADD SHIFT AWAY
If you add: shift equilibrium away from what you added.
TAKE AWAY SHIFT TOWARDS
If you remove: shift equilibrium towards what you took away.

5. Concentration
Changing the amount, or concentration, of any reactant or product in a system at equilibrium disturbs the equilibrium.
Removal of products used to increase yield of products.
Same goes for reactants

6. Le Châtelier’s Principle
Changes in Concentration continued
aA + bB  cC + dD
Change
Shifts the Equilibrium
Increase concentration of product(s)
Left (reactants)
Decrease concentration of product(s)
Right (products)
Increase concentration of reactant(s)
Right (products)
Left (reactants)
Decrease concentration of reactant(s)

7. Pressure and Volume
A change in pressure or volume affects only an equilibrium that has an unequal number of moles of reactants and products.
Increase in pressure results in a shift toward low pressure side or fewer number of moles. (Due to number of collisions)
Increase in volume results in a shift toward high pressure side or greater number of moles.

8. Le Châtelier’s Principle
Changes in Volume and Pressure
aA + bB  cC + dD
Change
Shifts the Equilibrium
Increase pressure
Side with fewest moles of gas
Decrease pressure
Side with most moles of gas
Increase volume
Side with most moles of gas
Decrease volume
Side with fewest moles of gas
14.5

9. Temperature Increase temp. shift to products
Exothermic -H, heat is a product
Endothermic, +H, heat is a reactant
Increase temp. shift to products
Decrease temp. shift to reactants
Increase temp. shift to reactants
Decrease temp. shift to products

10. Le Châtelier’s Principle
Adding a Catalyst
does not shift the position of an equilibrium system
system will simply reach equilibrium sooner
uncatalyzed
catalyzed
Catalyst lowers Ea for both forward and reverse reactions.
Catalyst does not change equilibrium constant or shift equilibrium.
14.5

11. CO (g) + 3H2(g)  CH4 (g) + H2O (g)+ heat 4  2
Add CO
Remove H2
Add CH4
Remove H2O
Decrease volume
Increase volume
Increase pressure
Decrease pressure
Increase temp.
Decrease temp.
 products
 reactants