Transcript Le Chteliers Principle 2009

Le Chatlier’s Principle
Le Châtelier’s Principle
 Le Châtelier’s Principle: if stress is applied to a
system in dynamic equilibrium, the system
changes to relieve the stress

3 types of stress
Concentration
 Temperature
 Pressure

 Website Demo:
http://www.mhhe.com/physsci/chemistry/essentialche
mistry/flash/lechv17.swf
Le Châtelier’s Principle
 Concentration
 Example: Carbonic Acid
H2CO3
Add CO2
CO2 + H2O
Remove CO2

What will happen if…


I add CO2?
• Make more reactants because more collisions with the products will
occur
• A stress was applied and the system compensated for this change
What will removing CO2 do?
• Shift to make more products
Le Châtelier’s Principle
 Temperature
 Think of heat as a reactant or product based on if the reaction is
exothermic or endothermic
 Example: exothermic formation of SO3
2SO2 + O2
Add heat
Remove heat
2SO3
Exothermic Reaction: (think of heat as a product)
increase temperature = shift toward reactants
Endothermic Reaction: (think of heat as a reactant)
increase temperature = shift toward products
+ heat
Le Châtelier’s Principle
 Pressure
 Only affects equilibrium that has an unequal number of moles of
gaseous reactants and products
 Example: Formation of ammonia
N2 + 3H2
Decrease Pressure
Increase pressure
2NH3
Activity…
 Due today
 Turn in 1 per pair of students
 All waste can go down the drain