Chemical Equilibrium

1
Chemical Equilibrium
A reversible reaction can go in either the
forward or reverse directions
A
B

D
C

Equilibrium is dynamic as both the forward and
reverse reactions continue At equilibrium the
forward and reverse rates are equal
2
Le Chateliers Principle
If a stress is applied to a system at
equilibrium, the system adjusts to relieve the
stress
CoCl42-
H2O
4Cl-
Co(H2O)62


H -
H
Exothermic (Heating)
Endothermic ( Cooling)
3
Le Chateliers Principle
If a stress is applied to a system at
equilibrium, the system adjusts to relieve the
stress
CrO42-
Cr2O72-
2H

H2O

4
Le Chateliers Principle
If a stress is applied to a system at
equilibrium, the system adjusts to relieve the
stress
Fe(CNS)2-
FeCl3

CNS-
3Cl-

5
Le Chateliers Principle
H2O
Co(H2O)62
CoCl42-
4Cl-


H
H -
Exothermic (Heating)
Endothermic ( Cooling)
What happens if the red solution is heated ?
Heating is a stress
Le Chatelier states the opposing reaction occurs
ie the reverse reaction
The cooling reaction occurs
Turning red into blue
6
Haber process
Manufacture of ammonia NH3 for the fertilizer
industry
2 NH3
N2
3 H2
H - 92.4

2
NH3
Kc
3
H2
N2
x
7
Haber process
Manufacture of ammonia NH3 for the fertilizer
industry
2 NH3
N2
3 H2
H - 92.4

• Le Chateliers principle predicts the yield of
  NH3 is maximised by
• Low temperature
• High pressure

Actual temp used is 500oC (as lower temp reduces
the rate )
Pressure used is 200 ATM
8
Contact process
Manufacture of Sulfuric acid H2SO4
2 SO3
2SO2
O2
H - 196

• Le Chateliers principle predicts the yield of
  SO3 is maximised by
• Low temperature
• High pressure

Actual temp used is 450 oC (as low temp reduces
the rate )
Pressure used is 1 ATM