FSc Notes Chemistry Part 1 Chapter 8 Chemical Equilibrium Lecture 2
Chemical Equilibrium:
That state of a reversible chemical reaction, at which the rate
of forward reaction becomes equal to the rate of reverse reaction, is known as chemical
equilibrium.
At the state of chemical equilibrium there is no more change
in the concentration of reactants and products but becomes constant although the reaction does not
stop but retains dynamically.
The chemical equilibrium can be explained by considering the
following
Example :
H2(G) + I2(g) 2HI
At the beginning, the concentration of reactants (H2+I2) is maximum,
hence the rate o9f forward reaction will be high and only for ward reaction will occur. After
sometime, enough amount of products (HI) is formed and reverse reaction starts, the rate of
forward reaction will be high than rate of reverse reaction. After sometime, the concentration of reactants
decreases enough and thus, rate of reverse reaction increases enough.
After sometime, the rate of forward reaction is just equal
to the rate of reverse reaction and the concentration of reactants and products becomes constant and
no more change occur in them, although the reaction does not stop. This is, what is known
as the equilibrium state.
It is important to note that it is not necessary, that at
equilibrium state concentration of reactants will be equal to the concentration of the products. May be,
the concentration of reactants is more than that of the products at equilibrium and undergoes no more
change or nay be the concentration of the products is more than that of the reactants and undergoes no
more change or the concentration of reactants may be equal t the concentration of products at equilibrium
and undergo no more change.
Types of Equilibrium:
There are two types of equilibrium.
- Homogeneous equilibrium.
- Heterogeneous equilibrium.
Homogeneous equilibrium.
The reversible reactions in which all the reacting
substances are in same physical state i.e all gases liquids or solids. e.g consider the following equilibrium system of a
reversible reaction
N2O4 ---------------> 2NO2(g)
Here all the reacting substances are in gaseous state.
Heterogeneous equilibrium.
The reversible reactions in which the reacting substances
(reactants & products) are in different physical states are known as heterogeneous equilibrium. e.g
CaCo3 -------------->CaO(S) + Co2(g)
In the above equilibrium system it is clear that the
reacting substances are in different physical states.
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