Transcript 7.05 Le Châtelier’s Principle Le Châtelier’s Principle Equilibrium A state in which opposing forces or influences are balanced. • What would happen if he.

7.05
Le Châtelier’s Principle
Le Châtelier’s Principle
Equilibrium
A state in which opposing forces or influences are balanced.
• What would happen if he puts more weigh on his right foot?
Definition
• Le Châtelier’s Principle: When stress is
applied to a system in equilibrium, the
reaction will shift in a direction that
relieves the stress, and a new equilibrium
will be established.
• Applied Stresses
– Changes in concentration.
– Changes in Pressure.
– Changes in temperature.
Four Scenarios
A+B
C+D
Concentration
3
• If A reactant/product is added to the system at equilibrium, the
equilibrium position will shift away from what was added to
lower the concentration of the added component.
• If a reactant/product is removed from a reaction system at
equilibrium, the equilibrium system will shift toward the
substance that was removed in order to replace some of what
was removed.
Practice – Which way does the reaction go?
• 1.) 2H2+O2
2H2O
• 2.) 2NO+O2
2NO2
(If you increase O2 )
(If you increase NO2 )
• 3.) A + B
C
(If you decrease C )
• 4.) A + B
C
(If you decrease A )
Pressure & Volume
When the pressure of a system at
equilibrium is increased, due to a decrease
in volume, the system will shift in the
direction that decreased the total moles of
gas in the system to minimize the stress.
(Shift towards side with less moles)
Pressure & Volume
Decrease volume/Increase Pressure – By shifting to the right, 4 moles of reactant are used
up to produce every 2 moles of product, thus reducing the overall moles of gas present in
the system.
Pressure & Volume (4 total moles)
(2 total moles)
The opposite is true if the volume of the container
is increased. The system will compensate for the
increase in volume and decrease in pressure by
shifting toward the side of the equation that has a
greater total number of moles of gas.
Pressure & Volume - Practice
(4 total moles)
( ___ total moles)
1.) How many moles of ammonia gas are on the
right side of the equation (product side)?
2.) Which way would the reaction shift if there is a
increase in pressure?
3.) If the volume was decreased (increase in
pressure) would there be more or less collisions
between the reactants?
Effect of a Change in Temperature
• If the forward reaction is endothermic, write energy as a
reactant on the left side of the equation. (+ΔH)
Energy + A + B
C+D
• If the forward reaction is exothermic, write energy as a
product on the right side of the equation. (–ΔH)
A+B
C + D + Energy
Temperature - Practice
A+B
C+D
1.) If energy was added to the reactants side of the above
equation which way would the system shift?
2.) Label the following reactions as Endothermic or Exothermic.
a.) Energy + N2O4
b.) C + O2
2NO2
CO2 + Energy
Additional Practice – Circle the correct answer
H2 + O2
H2O
1.) Adding more of H2 or O2 will cause the system to shift
Left / Right to reach a new equilibrium.
2.) Adding more of H2O will cause the system to shift
Left / Right to reach a new equilibrium.
3.) For a gaseous reaction If the pressure was decreased
there would be more / less collisions between the
reactants.
4.) The system will shift towards/away from the side of the
equation where energy is written.