Increases
a stage reaches when the rate of forward reaction become equal to rate of
reverse reaction and after this there is no further change in the concentration
of the substances. At this stage the reaction attains a state of equilibrium
which is also called dynamic equilibrium.
LE
CHATELIER’S PRINCIPLE:
Le’
Chatelier’s principle states that if a reversible reaction is in equilibrium is
disturbed by changing the conditions like change in concentration, change in
temperature or change in pressure, the
reaction will adjust itself in such a way as to mollify the effect of this
disturbance either by shifting itself in the forward or reverse direction.
APPLICATIONS
OF LE’CHATELIER’S
From
appropriate information of a reversible reaction at equilibrium Le’chatelier’s
principle is helpful to deduce qualitatively the effect of change in
concentration, pressure temperature or the pressure of a catalyst ar
equilibrium of a reversible reaction.
THE
EFFECT OF CHANGE IN CONCENTRATION:
For a
reversible reaction at equilibrium due to change in concentration position of
equilibrium changes but the equilibrium constant remains the same. For
reversible reactions equilibrium can easily be established in a closed vessel
especially for gas phase reversible reactions. If a reversible reaction has
attained the equilibrium position and at this stage of a certain amount of
reactant is added from outside the equilibrium position will be shifted in the
forward direction. Similarly addition of product from outside will shifted the
reaction in reverse direction likewise, decrease in concentration of reactants
will favour reverse reaction and decrease in concentration of products will
favour reaction for example the formation of a ester
At
equilibrium if we increase the concentration of ethanol in the mixture. The
position of equilibrium is disturbed. By applying Le’ Chatelier’s principle we
can deduce that more ethyl ethamoate and water will form and the concentration
of ethanol and ethanoic acid will fall until a new position of equilibrium is
established, Thus, the position of equilibrium moves towards the product i.e;
forward direction.
THE
EFFECT OF PRESSURE ON THE EQUILIBRIUM POSITION:
Pressure
has no effect on solid, liquid and aqueous phase reactants or products. Whereas
pressure has significant effect on gas phase (state) reactions. As the pressure
on gases increases their volume decreases. In gases numbers of moles of gas are
directly proportional to volume of gas i.e; n
V Hence, by applying pressure on mixture of
reversible gases at equilibrium the position of equilibrium moves towards
lesser number of moles of gases. i.e; towards lesser volume of hases. For
example.
N
+ 3H
2NH
In
Haber’s process forward reaction is favoured
at high pressure because the forware direction there are lesser number
of moles or less volume.
Similarly
formation of nitric oxide by the oxidation of ammonia gas is favoured at low
pressure.
4NH
+ 5O
4NO(g)+
6H2O(g)
Thus,
at equilibrium of pressure is released and volume is allowed to expend, then
more ammonia reacts with oxygen to form nitric oxide and steam. Hence position
of equilibrium at low pressure moves towards the forward i.e; towards the
products. However change in pressure no effect on those gaseous reactions in
which there are equal number of gaseous molecules (moles) on both rides of the
equations e.g;
H
+ I
2HI(g)
Similarly
pressure have no effect on the reaction of iron with steam
3Fe(s)
+ 4H2O(g)
Fe3O
+ 4H
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