Electrochemistry

(i) Weak electrolytes: When the concentration of weak electrolyte becomes very low, its degree of ionisation rises sharply. There is sharp increase in the number of ions in the solution. Hence, the molar conductivity of a weak electrolyte rises steeply at low concentration.

(ii) Strong electrolytes: The molar conductivity of a strong electrolyte decreases slightly with the increase in concentration. This decrease is due to the increase in interionic attractions as a result of greater numbr of ions per unit volume. With dilution, the ions are far apart, inter ionic attractions become weaker and conductance increases.

Faraday's first law. The amount of substance produced at an electrode during electrolysis is directly proportional to the quantity of electricity passed through the electrolyte.

Faraday's first law. The amount of substance produced at an electrode during electrolysis is directly proportional to the quantity of electricity passed through the electrolyte.

                                   $\mathrm{W}\propto \mathrm{Q}$

or                               $\mathrm{W}\propto$It

or                                 W = ZIt

where W is the mass of substance produced at an electrode.
I is current in amperes
t is time in seconds for which current is passed.
Z is electro-chemical equivalent of substance.
Faraday's second law: It states that the masses of different substances liberated or dissolved by the same amount of electricity passed is directly proportional to their chemical equivalents. Or in other words “the same quantity of electricity will produce or dissolve chemically equivalent quantities of all substances.”
Mathematically,

$\frac{\mathrm{Mass} \mathrm{of} \mathrm{A} \mathrm{deposited}}{\mathrm{Mass} \mathrm{of} \mathrm{B} \mathrm{deposited}}=\frac{\mathrm{Equivalent} \mathrm{mass} \mathrm{of} \mathrm{A}}{\mathrm{Equivalent} \mathrm{mass} \mathrm{of} \mathrm{B}}$

Thus, we can say that the same quantity of electricity is required to produce one equivalent of any substance. It is called Faraday, F. It is equal to 96500 coulombs, and is equal to the charge on one mole of electrons.

The cell potential is simply related to the free energy change for the reaction. In an electro chemical cell the system does work by transferring the electric charge through an external circuit. The free energy change $∆\mathrm{G}$ is equal to electrical work done.

$∆\mathrm{G} = {\mathrm{W}}_{\mathrm{electrical}}$

For reaction occurring in a electrochemical cell whose electrodes differ in potential by E_cell, the work done when amount of charge nF is transferred is given by
                   ${\mathrm{W}}_{\mathrm{elect}} = -{\mathrm{nFE}}_{\mathrm{cell}}$
∴                   $∆\mathrm{G} = -{\mathrm{nFE}}_{\mathrm{cell}}$
Under standard state conditions
ΔG° = – n FE°_cell.