UNIT 3 ELECTROCHEMISTRY
- An electrochemical cell consists of two metallic electrodes dipping in electrolyte solution.
- Electrochemical cells are of two types:
- Galvanic cell: The chemical energy of a spontaneous redox reaction is converted into electrical work.
- Electrolytic cell: The electric energy is used to carry out a non-spontaneous redox reaction.
- The standard electrode potential for any electrode dipping in an appropriate solution is defined with respect to standard electrode potential of hydrogen electrode taken as zero.
- The standard potential of the cell can be obtained by taking the difference of the standard potentials of cathode and anode.
- Concentration dependence of the potentials of the electrodes and the cells are given by Nernst equation.
- The conductivity (κ) of an electrolytic solution depends on the concentration of the electrolyte, nature of solvent and temperature.
- Molar conductivity is defined by κ/c where c is the concentration.
- Conductivity decreases with decrease in concentration but molar conductivity increases with decrease in concentration. It increases slowly with decrease in concentration foe strong electrolytes while the increase is very steep for weak electrolytes in very dilute solutions.
- Law of independent migration: Molar conductivity at infinite dilution for an electrolyte is the sum of the contribution of the molar conductivity of the ions in which it dissociates.
- Ions conduct electricity through the solution but oxidation and reduction of the ions takes place at the electrodes in an electrochemical cell.