Question

a) Define Kohlrausch's law of independent migration of ions. Give its applications.
b) Describe the salient features of the Collision theory of reaction rates of bimolecular reactions.

Answer 1

(a)
Kohlrausch's law of independent migration of ions:
At infinite dilution, each ion migrates independently of its co-ion and makes its own contribution to the total molar conductivity of an electrolyte irrespective of the nature of other ion with which it is associated.
Thus, ${\Lambda }_0={\lambda }_{+}^0+{\lambda }_{-}^0$
Here,
${\Lambda }_0=$ the molar conductivity of the electrolyte at zero concentration
${\lambda }_{+}^0=$ the molar conductivity of cation at zero concentration
${\lambda }_{-}^0=$ the molar conductivity of anion at zero concentration
For example, ${\Lambda }_0\left(HCl\right)={\lambda }_0\left(H^{+}\right)+{\lambda }_0\left(C{l}^{-}\right)$
Here,
${\Lambda }_0\left(HCl\right)=$ the molar conductivity of HCl at zero concentration
${\lambda }_0\left(H^{+}\right)=$ the molar conductivity of protons at zero concentration
${\lambda }_0\left(C{l}^{-}\right)=$ the molar conductivity of chloride ions at zero concentration
Application:
The molar conductivity of an electrolyte (particularly weak electrolyte) at zero concentration can be calculated. For example, the molar conductivity ( at zero concentration) of acetic acid can be calculated from the molar conductivities ( at zero concentration) of HCl, sodium acetate and sodium chloride by using the following expression.
${\Lambda }_0\left(C{H}_{3}COOH\right)={\Lambda }_0\left(HCl\right)+{\Lambda }_0\left(C{H}_{3}COONa\right)-{\Lambda }_0\left(NaCl\right)$
(b)
The salient features of the Collision theory of reaction rates of bimolecular reactions:
(i) The reaction molecules are assumed to be hard spheres
(ii) When molecules collide with each other, the reaction will occur.
(iii) Collision frequency (Z) is the number of collisions per second per unit volume of the reaction mixture.
(iv) For a bimolecular elementary reaction
$A+B\to$ products
Rate $=Z{e}^{-E_a/RT}$
(v) All collisions do not result in reaction.
(vi) The probability factor (p) also called steric factor accounts for effective collisions.
Rate $=pZ\cdot e^{-E_a/RT}$
(vii) The proper orientation of reactant molecules result in bond formation. No product is formed with improper orientation.