Revision: Electrochemistry Chemistry HSC Science (General) 12th Standard Board Exam Maharashtra State Board

The electrode at which the reduction occur is called cathode.

The electrode at which the oxidation occur is called anode.

Fuel cells are the galvanic cells in which the energy of combustion of fuels like hydrogen, methanol, etc., is directly converted into electrical energy.

Cell constant is the ratio of the distance between the electrodes divided by the area of cross-section of the electrode. It is denoted by b.
Thus, Cell constant = b =`l/a`. It is expressed in unit m⁻¹.

The limiting molar conductivity of an electrolyte is defined as its molar conductivity when the concentration of the electrolyte in the solution approaches zero.

When the concentration of an electrolytic solution placed between electrodes of a conductivity cell placed at a unit distance having an area of cross-section sufficient to accommodate enough volume of solution containing one mole of electrolyte approaches zero, then the conductance of the solution is known as limiting molar conductivity.

Molar conductivity is the conductance of a volume of solution containing 1 mole of dissolved electrolyte when placed between two parallel electrodes 1 cm apart and large enough to contain between them all the solution.

The conductivity, which is shown by all the ions when 1 mol of electrolyte is dissolved in the solution, is called molar conductivity; it is expressed by ∧_m (lambda). If 1 mol of electrolyte is present in V_m cm³ of electrolyte solution, then ∧_m = κ × V

= `(kappa xx 1000)/"Molarity" = (kappa xx 1000)/M`

Its unit is ohm⁻¹ cm² mol⁻¹ or S cm² mol⁻¹.

Nernst equation can be given as,

`E = E^circ - (2.303 RT)/(nF) log_10  [["Products"]]/[["Reactants"]]`

where,

E° = Standard potential of electrode or cell,

n = Number of moles of electrons used in reaction,

F = Faraday = 96500 C/mol e⁻,

[Products] = Concentration of products,

[Reactants] = Concentration of reactants,

T = Temperature in K and

R = Gas constant = 8.314 J K⁻¹ mol⁻¹

Kohlrausch law states that at infinite dilution of the solution, each ion of electrolyte migrates independently of its co-ions and contribute independently to the total molar conductivity irrespective of the nature of other ion.

Kohlrausch’s law states that the molar conductivity of an electrolyte at infinite dilution is the same as the sum of the anions' and cations' limited molar conductivities.

`∧_m^° = v_+  λ_+^° + v_-  λ_-^°`

Here `λ_+^°` and `λ_-^°` are limiting molar conductivities of cations and anions.