Chapter 2 — Electrochemistry

Chapter 2 of the Class 12 Chemistry NCERT textbook, "Electrochemistry", covers the interconversion of chemical and electrical energy, including galvanic cells, the Nernst equation, electrolytic conductance, Faraday's laws of electrolysis, batteries, fuel cells, and corrosion as an electrochemical process.

• Redox energy in cells — The chapter explains how spontaneous redox reactions drive galvanic cells to produce electrical energy, and how an external supply forces non-spontaneous reactions in electrolytic cells — two mirror-image processes that frame the whole subject of electrochemistry.
• Linking potential, energy and equilibrium — It ties cell potential to thermodynamics, deriving the Nernst equation for EMF at varying ion concentrations and connecting standard cell potential to Gibbs energy and the equilibrium constant, so a measured voltage reveals a reaction's spontaneity and extent.
• Conductance of electrolytes — Ionic conduction is treated through molar conductivity and Kohlrausch's law of independent ion migration, showing how conductivity changes with dilution and how limiting values for weak electrolytes are obtained.
• Applications: batteries, fuel cells and corrosion — The ideas are applied to real devices — primary and secondary batteries and hydrogen-oxygen fuel cells — and to the unwanted electrochemistry of rusting, where an iron surface behaves as a tiny galvanic cell.

1. 01A galvanic cell converts Gibbs energy of a spontaneous redox reaction into electrical work; the Daniell cell (Zn/Cu²⁺) has a standard EMF of 1.1 V.
2. 02The Nernst equation E(cell) = E°(cell) – (RT/nF) ln Q relates cell potential to the reaction quotient; at 298 K it simplifies to E(cell) = E°(cell) – (0.059/n) log Q.
3. 03Standard cell potential, standard Gibbs energy, and equilibrium constant are interrelated: DrG° = –nFE°(cell) and E°(cell) = (2.303RT/nF) log Kc.
4. 04Molar conductivity (Λm = κ/c) increases on dilution for both strong and weak electrolytes; for strong electrolytes Λm = Λ°m – A√c (Debye–Hückel–Onsager equation).
5. 05Kohlrausch's law states that limiting molar conductivity equals the sum of individual ionic contributions: Λ°m = ν₊λ°₊ + ν₋λ°₋; it is used to find Λ°m of weak electrolytes.
6. 06Corrosion of iron is an electrochemical process in which the metal surface acts as a galvanic cell: iron is oxidised at the anode (E° = –0.44 V) and oxygen is reduced at the cathode (E° = +1.23 V), giving an overall E°(cell) of 1.67 V.