AP Chemistry Handout
15.4 Le Châtelier’s Principle
 Henri-Louis Le Châtelier* (1850–1936), a French industrial chemist: If a
system at equilibrium is disturbed by a change in temperature, pressure, or
a component concentration, the system will shift its equilibrium position so
as to _________ the effect of the disturbance.
1. Change in Reactant or Product Concentration
A(g) + B(g) ⇋ C(g) + D(g)
Add reactant
Shift to ________
Add product
Shift to ________
Remove reactant
Shift to ________
Remove product
Shift to ________
 Will the change of concentration change the value of K? Why?
2. Change in temperature
 For an exothermic reaction
H2SO4 + NaOH→Na2SO4+H2O
Increase temperature
Shift to ________
Decrease temperature
Shift to ________
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AP Chemistry Handout
 For an endothermic reaction:
H2O2→ H2O+O2
Increase temperature
Shift to ________
Decrease temperature
Shift to ________
 Will the change of temperature change the value of K? How?
3. Change in volume or pressure
 What’s the most common way to change the pressure of a system?
At constant temperature, reducing th
e volume of a gaseous equilibrium
mixture causes the system to shift in the direction that ________ the number of
moles of gas. Increasing the volume causes a shift in the direction that produces
______ gas molecule
 For this reaction ：H2(g)+Cl2(g) → 2HCl(g)，
Increase pressure
Decrease pressure
Shift to ________
Shift to ________
 For this reaction ：N2(g) + 3 H2(g) ⇋ 2NH3(g)，
Increase pressure
Decrease pressure
Shift to ________
Shift to ________
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AP Chemistry Handout
4. The effect of catalyst
A catalyst increases the rate at which equilibrium is achieved but does not
change the composition of the equilibrium mixture.
 Energy graph of adding catalyst:
 Graph of rate:
 Graph of product:
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