Chemical Equilibrium
A reversible reaction can go in either the
forward or reverse directions
A
+
B
C
+
D
Equilibrium is dynamic
as both the forward and reverse reactions continue
At equilibrium the forward and reverse rates are equal
Le Chateliers Principle
If a stress is applied to a system at equilibrium, the
system adjusts to relieve the stress
CoCl42- +
H2O
H= +
Endothermic ( Cooling)
Co(H2O)62+
+
4ClH= -
Exothermic (Heating)
Le Chatelier’s Principle
If a stress is applied to a system at equilibrium, the
system adjusts to relieve the stress
2+
Cr
O
2 7
-
H2O
CrO42-
+
2H+
Le Chateliers Principle
If a stress is applied to a system at equilibrium, the
system adjusts to relieve the stress
FeCl3
+
CNS-
Fe(CNS)2-
+
3Cl-
Le Chatelier’s Principle
CoCl42-
+
Co(H2O)62+
H2O
+
H= +
4ClH= -
Exothermic (Heating)
Endothermic ( Cooling)
What happens if the red solution is heated ?
Heating is a stress
Le Chatelier states the opposing reaction occurs
The cooling reaction occurs
ie the reverse reaction
Turning red into blue
Haber process
Manufacture of ammonia NH3 for the fertilizer industry
N2
+
2 NH3
3 H2
2
NH3
Kc =
N2
x
H2
3
H= - 92.4
Haber process
Manufacture of ammonia NH3 for the fertilizer industry
N2
+
3 H2
2 NH3
H= - 92.4
Le Chatelier’s principle predicts the yield of NH3 is maximised by
1. Low temperature
2. High pressure
Actual temp used is 500oC (as lower temp reduces the rate )
Pressure used is 200 ATM
Contact process
Manufacture of Sulfuric acid H2SO4
2SO2
+
O2
2 SO3
H= - 196
Le Chatelier’s principle predicts the yield of SO3 is maximised by
1. Low temperature
2. High pressure
Actual temp used is 450 oC (as low temp reduces the rate )
Pressure used is 1 ATM