Page 5 - Microsoft Word - Equilibrium State key notes

Favourable conditions for some chemical equilibria to get higher yield of product.

Calculation of the Degree of Dissociation (α) from Density Measurement
α = D – d / d

where, D = theoretical vapour density

d = observed vapour density

Now, molecular mass = 2 * VD

∴ α = Mc – Mo / Mo
where, Mc = calculated molecular weight
Mo = observed molecular weight

IONIC EQUILIBRIUM

 Ionic Equilibrium: Equilibrium established between unionized molecules and
anions in solution of weak electrolytes.

 The strong electrolytes are completely dissociated. In weak electrolytes there
is equilibrium between the ions and the unionized electrolyte molecules.
According to Arrhenius, acids give hydrogen ions while bases produce
hydroxyl ions in their aqueous solutions.
Limitation of Arrhenius concept: The concept is applicable only to aqueous
solutions and it does not account for the basicity of substances like ammonia
which does not have hydroxyl group.

 Brönsted-Lowry on the other hand, defined an acid as a proton donor and a
base as a proton acceptor. When a Brönsted-Lowry acid reacts with a base, it
produces its conjugate base and a conjugate acid corresponding to the base
with which it reacts. Thus a conjugate pair of acid-base differs only by one
proton. Lewis further generalised the definition of an acid as an electron pair
acceptor and a base as an electron pair donor. The expressions for ionization
(equilibrium) constants of weak acids (Ka ) and weak bases (Kb) are developed
using Arrhenius definition.