FSc Notes Chemistry Part 1 Chapter 8 Chemical Equilibrium Lecture 5
Applications of Le- Chatelier's Principle : (Effect of Change in Conditions upon Equilibrium)
Le – Chatelier's principle is used to predict, how the
variable like concentration. Temp, pressure etc, affect the position of equilibrium.
This principle also has a valuable application in prediction
the condition for maximum yield of a particular in a reversible reaction.
1) Effect of Concentration:
According to Le – Chatelier's principle an increase in the
concentration of any the reactants, shifts the equilibrium to the right i.e forward reaction increases
similarly an increase in the concentration of any of the products shifts the equilibrium to the left i.e reverse
reaction increases Same examples are as follow
N2 + 3H2--------------------2NH3
The addition of H2 and N2 would shift the equilibrium to the
right. Thus the use of excess of N2 yield of NH3
FeCl3+n3NH4CNS --------------------Fe ( CNS)3 + 3NH4C ff2
Yellow colorless blood red colorless The addition of Fecl3 , shifts the equilibrium to the right
& thus more Fe (CNS)3 (blood red) is formed , forward reaction increases. Similarly the addition of NH4Cl , shift the equilibrium to
the left resulting in the formation of more NH4CNs & FeCl3 i.e reverse reaction is increased.
2) Effect OF Pressure:
In case of reactions ( reversible ) in which the total
volume of reactants is equal to the total volume of the products , the equilibrium is not affected by
change in pressure.
e.g
1. CO(g) + H2O(g) ---------------- CO2(g) + H2(g)
1. CO(g) + H2O(g) ---------------- CO2(g) + H2(g)
1 vol 1 vol 1vol 1vol
Total 2 vol 2 vol
Total 2 vol 2 vol
2. N2 (g) + O2(g) --------------- 2NO(g)
1vol 1 vol 2 vol
Total 2 vol 2 vol
Change of pressure has no effect upon the equilibrium in the
above mentioned equilibrium system between total volume of reactants is equal to total
volume of products. In case of reactions ( reversible ) where the total volume
of reactants is not equal to the volume of the products, with an increase of pressure the
equilibrium system shifts towards the smaller volume.
In case of these reversible reactions in which the volume of reactants is greater than that of the products, the equilibrium shifts to the right side i.e more
products are formed by increasing the pressure of the system.
In case of those reversible reactions in which the volume of products is greater than that of reactants increases with increase of pressure.
In case of those reversible reactions in which the volume of products is greater than that of reactants increases with increase of pressure.
3) Effect of Temperature:
There are two types of reversible reactions i.e endothermic
and exothermic.
In case of endothermic reversible reactions, heat is
absorbed in the forward direction and the same is evolved in the reverse direction and the same is absorbed
in reverse direction. With increase of temperature of an reversible reaction (
endothermic or exothermic ) at equilibrium, the equilibrium always shifts in that direction
where the temperature decreases. This in case of endothermic reaction (reversible) the equilibrium
with crease of temperature . shifts to the forward direction
Examples :
Reversible endothermic Reactions
N2+O2+Heat ………………..2NO
H2S+O2+Heat ………………….H2 + S
As these are endothermic breakfronts thus in decease of
temperature Shifts The equilibrium in forward direction . As the reaction are exothermic thus an increase in
temperature will shift the equilibrium in
reverse direction. Thus more amount of NH3& SO2 can be formed by lowering
the temperature.
4) Effect of Catalyst:
According to Le – Chatelier's principle, catalyst has no
effect upon the equilibrium except the equilibrium reaches earlier in the presence of a catalyst. Actually the catalyst increases the speed of both forward
& reverse reactions of a reversible reaction to the some extent, therefore the equilibrium
remains unchanged. However it is reached earlier.
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