What are the important features of equilibrium constant? Discuss any two applications of equilibrium constant.

Explanation

The ratio of product of molar concentrations of products to the product of molar concentrations of reactants is called equilibrium constant `(K_(c))`
Ex : `aA+bB hArr cC+dD`
`K_(C)=([C]^(2)[D]^(d))/([A]^(a)[B]^(b))`
` to K_(c)` for reverse reaction is the inverse of the `K_(c)` for the reaction in the forward direction.
`to` Concentration equilibrium constant `(K_(C))` and pressure equilibrium constant `(K_(p))` are related as follows
`K_(p)=K_(C)(RT)^(Deltan)`
`Deltan=n_(P)-n_(R)`
`to` While writing Kc expression pure liquids, pure solids concentration are ignored Applications :
a) In predicting the extent of reaction :
The numerical value of the equilibrium constant for a reaction indicates the extent of the react tion. But it is important to note that an.equilibrium constant does not give any information about the rate at which the equilibrium is reached the Magnitude of `k_(e)` or `K_(p)` is directly proportional to the concentrations of products (as these appear in the numerator of equilibrium constant expression) and inversely proportional to the concentrations of the reactants (these appear in the denomina tor). This implies that a high value of K is suggestive of a high concentration of products and vice .versa.
We can make the following generalisation concerning the composition of equilibrium mixtures : If `K gt 10^(3)` products predominate over reactants, i.e., if `K_(c)` is very large, the reaction proceeds nearly to completion. Consider the following examples :
(a) The reaction of `H_(2)` with `O_(2)` at 500 K has a very large equilibrium `K_(c)=2.4xx10^(47)`
(b) `H_(2(g)) hArr 2HCl(g)` at 300 K has `K_(C)=4.0xx10^(31)`
(c) `H_(2_((g)))+Br_(2_(g)) hArr 2HBr_((g))` at 300 K, `K_(c)=5.4xx10^(18)`
If `K_(c) lt 10^(-3)` eactants predominate over products i.e, if `K_(c)` is very small the reaction proceeds rarely. Consider the following examples :
(a) The decomposition of `H_(2)O` into `H_(2) and O_(2)` at 500 K has a very small equilibrium constant.
`K_(c)=4.1xx10^(-48)`
(b) `N_(2_((g)))+O_(2_((g))) hArr 2NO_((g))`
at 298 K has `K_(c)=4.8xx10^(-31)`
If `K_(c)` is in the range of `10^(-3) "to" 10^(3)` appreciable concentrations of both reactants and products are present. Consider the following examples :
(a) for reaction of `H_(2)` with `I_(2)` give HI.

(b) Also, gas phase decomposition of `N_(2) O_(4)` to `No_(2)` is another reaction with a value of `K = 4.64 xx 10^(-3)` at `25^(@)C` which is neither too small nor too large. Hence equilibrium mixtures contain appreciable concentrations of both `N_(2)O and NO_(2)`.
These generarlisations are illustrated. b) In predicting the direction of reaction : A and K are compared to predict the direction of reaction.
(a) Q = K indicates that the reaction mixture is already at equilibrium.
(b) `Q lt K` iQ = K indicates that the reaction mixture is already at equilibrium.
(c) ` Q gt K` indicates that the reaction proceeds in the direction of reactants (Reverse reaction).