Le Chatelier`s Lesson PowerPoint
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Transcript Le Chatelier`s Lesson PowerPoint
Unit 17
Daily 2
What is Le Chatelier’s Principle?
Explore factors affecting equilibrium
2. Predict direction of equilibrium shift
3. Predict resulting changes in concentration
4. Make equilibrium serve your own evil purposes
1.
• Equilibrium is a RATE balance.
• Anything that can affect the rate of the forward or
reverse reaction can throw equilibrium off.
• What are the factors that affect reaction rate?
1)
2)
3)
4)
5)
Concentration
Pressure or Volume (gases)
Temperature
Surface Area
Catalysts/Inhibitors
“If a system at equilibrium is subjected to an external
stress, the equilibrium will shift to minimize the
effects of that stress”
The Steps of Le Chatelier’s Principle:
Stress: Adding or removing a reactant, adding or
removing a product, changing the pressure, volume, or
temperature.
2) Shift: The equilibrium will shift away from what is
added and towards what is removed.
3) Change in Concentration: The concentration of what is
being shifted towards increases, the concentration of
what is being shifted away from decreases.
1)
Fe3+(aq) + SCN-(aq) FeSCN2+(aq)
(colorless)
(red)
If more Fe3+ is added to the system, what will happen?
equilibrium shifts to the right
equilibrium shifts to the product side
the forward reaction is favored (forward shift)
How are concentrations affected?
[Fe3+] increases, [SCN-] decreases, [FeSCN2+] increases
How is Keq affected?
Keq does not change when changes in concentration cause a
shift in equilibrium
Fe3+(aq) + SCN-(aq) FeSCN2+(aq)
(colorless)
(red)
If more FeSCN2+ is added to the system, what will
happen?
equilibrium shifts to the left
equilibrium shifts to the reactant side
the reverse reaction is favored (reverse shift)
How are concentrations affected?
[Fe3+] increases, [SCN-] increases, [FeSCN2+] increases
Fe3+(aq) + SCN-(aq) FeSCN2+(aq)
(colorless)
(red)
If SCN- is removed from the system (by adding AgNO3 so
that AgSCN(s) precipitate forms), what will happen?
equilibrium shifts to the left
equilibrium shifts to the reactant side
the reverse reaction is favored (reverse shift)
How are concentrations affected?
[Fe3+] increases, [SCN-] increases (but also decreases
since it was removed), [FeSCN2+] decreases
Only affect an equilibrium system if gases are present
What is the relationship between moles of gas and
volume/pressure?
P = (nRT)/(V)
If pressure is increased (or volume decreased):
equilibrium will shift towards the side with FEWER
moles of gas to bring the pressure back down
If pressure is decreased (or volume increased):
equilibrium will shift towards the side with MORE
moles of gas to bring the pressure back up
N2(g) + 3H2(g) 2NH3(g)
(4 moles)
(2 moles)
If pressure is increased (volume decreased) on the
system, what will happen?
equilibrium shifts to the right
equilibrium shifts to the product side
the forward reaction is favored (forward shift)
How are concentrations affected?
[N2] decreases, [H2] decreases, [NH3] increases
Notes:
If the number of moles of gas are equal on both sides,
then the equilibrium can’t shift
H2(g) + I2(g) 2HI(g)
Make sure to only count the moles of GAS when
considering pressure effects on equilibrium
If temperature is increased in the system, what will
happen?
equilibrium will shift in the endothermic direction
the endothermic direction is away from the side with
heat
If temperature is decreased in the system, what will
happen?
equilibrium will shift in the exothermic direction
the exothermic direction is towards the side with heat
H2O
H
OH
H2O
H
H
OH
Which way does the see saw have to shift to reach equilibrium again?
H2O
H
H
OH
Which way does the see saw have to shift to reach equilibrium again?
SHIFT LEFT
H
H2O
H
More H2O is produced due to the shift in equilibrium
OH
H2
H2
N2
H2
NH3
N2 (g) + 3H2 (g) 2NH3 (g)
NH3
SHIFT RIGHT
H2
N2
H2
NH3
NH3
H2
SHIFT will occur to side with the least number of MOLES
N2 (g) + 3H2 (g) 2NH3 (g)
H2
H2
N2
H2
NH3
N2 (g) + 3H2 (g) 2NH3 (g)
NH3
SHIFT RIGHT
H2
N2
H2
NH3
NH3
H2
SHIFT will occur to side with the least number of MOLES
N2 (g) + 3H2 (g) 2NH3 (g)
Depends if reaction is Endothermic or Exothermic.
Endothermic: Heat on LEFT
Exothermic: Heat on RIGHT
HEAT
A
B
C
D
Increase Temperature… which way will the see saw tip?
A
B
HEAT
C
Which way will the reaction shift?
D
A
HEAT
B
C
Reaction will SHIFT LEFT
D
HEAT
A
B
C
D
DecreaseTemperature… which way will the see saw tip?
HEAT
C
D
B
A
Which way will the reaction shift?
HEAT
C
B
A
Reaction will SHIFT Right
D
HEAT
A
B
C
D
Increase Temperature… which way will the see saw tip?
HEAT
C
A
D
B
Which way will the reaction SHIFT?
HEAT
C
A
B
Reaction will SHIFT Right
D
HEAT
A
B
C
D
Decrease Temperature… which way will the see saw
tip?
HEAT
A
B
C
Which way will the reaction SHIFT?
D
HEAT
A
B
C
Reaction will SHIFT Left
D
2NO2(g) N2O4(g) + energy
(Dark Brown)
(Clear)