CBSE Class 12 Chemistry: Electrochemistry — Complete Notes 2026

Galvanic (Voltaic) Cell

• Converts chemical energy to electrical energy; spontaneous redox reaction
• Daniel cell: Zn(s) | ZnSO₄(aq) || CuSO₄(aq) | Cu(s); Zn = anode (−), Cu = cathode (+)
• EMF = E°cathode − E°anode; standard EMF calculated from standard electrode potentials

Nernst Equation

• E = E° − (RT/nF) ln Q = E° − (0.0591/n) log Q at 25°C
• At equilibrium: E = 0 and Q = K; therefore E° = (0.0591/n) log K
• Application: calculate cell EMF at non-standard concentrations

Conductance

• Resistance R = ρL/A; conductance G = 1/R; conductivity κ = 1/ρ
• Molar conductivity Λm = κ/c (in Sm²mol⁻¹)
• Kohlrausch's law: Λ°m = Σλ°₊ + Σλ°₋ (limiting molar conductivity)

Variation of Molar Conductivity

• Strong electrolytes: Λm = Λ°m − A√c (Debye-Hückel-Onsager equation); plot straight line
• Weak electrolytes: Λm increases steeply as c → 0; cannot extrapolate accurately
• Degree of dissociation α = Λm/Λ°m for weak electrolyte

Faraday's Laws of Electrolysis

• First law: mass deposited m = ZIt; Z = M/nF (electrochemical equivalent)
• Second law: same charge deposits equivalent masses of different substances
• 96485 C = 1 Faraday; deposits 1 gram-equivalent of any substance

Batteries and Fuel Cells

• Primary cell (dry cell): Leclanché cell; non-rechargeable; Zn anode, MnO₂ cathode
• Lead storage battery: 2V per cell, 6 cells = 12V; rechargeable
• Hydrogen fuel cell: H₂ + ½O₂ → H₂O; EMF ~1.23 V; high efficiency, no pollution

CBSE Exam — Electrochemistry

• Calculate EMF of cell Cu|Cu²⁺(0.01M) || Ag⁺(0.1M)|Ag using Nernst equation
• Electrolysis of AgNO₃ solution: 0.5 A for 2 hours; find mass of Ag deposited
• Explain why electrolyte conductivity decreases on dilution for weak electrolytes