Electrochemistry notes class – 12/JEE/NEET

Description

CHEMISTRY | CLASS XII | ELECTROCHEMISTRY

(Comprehensive Notes for Board & Competitive Exams)

Module 1: Fundamentals of Electrochemical Cells

• Introduction to Electrochemistry: Definition and scope—the study of interconversion of chemical energy and electrical energy through redox reactions.¹

   

• Electrochemical Cells: Devices where redox reactions occur to either generate or consume electrical energy.²

   

  • Galvanic (Voltaic) Cells: Converts chemical energy into electrical energy (spontaneous reactions, ³$Delta G < 0$).⁴

     

    • Components: Anode (Negative, Oxidation), Cathode (Positive, Reduction).⁵

       

    • Function of the Salt Bridge (Maintains electrical neutrality and completes the circuit).
  • Electrolytic Cells: Converts electrical energy into chemical energy (non-spontaneous reactions, ⁶$Delta G > 0$).⁷

     

    • Components: Anode (Positive, Oxidation), Cathode (Negative, Reduction).⁸

       

  • Key Distinction: Detailed comparison table of Galvanic vs. Electrolytic Cells.

Module 2: Electrode Potential and the Nernst Equation

• Electrode Potential ($E$): The potential difference developed between a metal electrode and the electrolytic solution of its ions.
  • Standard Electrode Potential ($E^{circ}$): Electrode potential measured under standard conditions ($1 text{ M}$ concentration, $1 text{ atm}$ pressure for gases, $298 text{ K}$).
  • Standard Hydrogen Electrode (SHE): The reference electrode ($E^{circ} = 0.00 text{ V}$).
• Cell Potential / EMF (⁹$E_{text{cell}}$): The difference between the reduction potentials of the cathode and the anode: ¹⁰

   

  $$E_{text{cell}} = E_{text{cathode}} – E_{text{anode}}$$
• Electrochemical Series: Arrangement of elements based on their standard reduction potentials—key for predicting reaction spontaneity.¹¹

   

• Nernst Equation: Relates electrode potential or cell EMF to the concentration of ions:
  $$E_{text{cell}} = E^{circ}_{text{cell}} – frac{RT}{nF} ln Q$$
  • Simplified form at $298 text{ K}$: The crucial formula for numerical problems.
  • Applications: Calculation of $E_{text{cell}}$ and determination of Equilibrium Constant ($K_c$).
• Gibbs Free Energy and EMF: The relationship between spontaneity (¹²$Delta G$) and cell potential: ¹³

   

  $$Delta G = -nFE_{text{cell}}$$
  • Calculation of Standard Gibbs Free Energy ($Delta G^{circ}$) and its relation to $K_c$.

Module 3: Conductance in Electrolytic Solutions

• Resistance ($R$) and Resistivity ($rho$): Definitions and $text{SI}$ units.
• Conductance ($G$) and Conductivity ($kappa$): Reciprocal concepts, definition of Specific Conductivity ($kappa$) as $G times (l/A)$.
• Molar Conductivity (¹⁴$Lambda_m$):¹⁵ Definition, formula, and $text{SI}$ units ($ Lambda_m = frac{kappa times 1000}{M}$).

   

• Variation of $kappa$ and $Lambda_m$ with Concentration/Dilution: Graphical representation and conceptual explanation for strong and weak electrolytes.
• Kohlrausch’s Law of Independent Migration of Ions:
  • Statement and mathematical form ($Lambda_{m}^{circ} = nu_{+} lambda_{+}^{circ} + nu_{-} lambda_{-}^{circ}$).
  • Applications: Calculating Molar Conductivity at Infinite Dilution ($Lambda_{m}^{circ}$) for weak electrolytes and determining the Degree of Dissociation ($alpha$).

Module 4: Electrolysis and Industrial Applications

• • Electrolysis: The process of chemical decomposition by passing an electric current through an electrolyte.¹⁶

     

    • Factors Affecting Product Formation: Nature of electrolyte, nature of electrode, and Overvoltage/Overpotential.
    • Preferential Discharge of Ions: Explanation based on standard reduction potentials.
  • Faraday’s Laws of Electrolysis:
    • First Law (¹⁷$m propto Q$): ¹⁸$m = ZIt$.¹⁹

       

    • Second Law: $m_1/m_2 = E_1/E_2$.
    • Numerical Formulas and applications.
  • Batteries (Primary and Secondary Cells): Detailed working principles, reactions, and uses.
    • Primary: Dry Cell (Leclanché Cell) and Mercury Cell.²⁰

       

    • Secondary: Lead Storage Battery and $text{Ni-Cd}$ Cell (Rechargeable).

• Fuel Cells: Introduction, working of the $text{H}_2-text{O}_2$ Fuel Cell, advantages, and environmental benefits.
• Corrosion: An electrochemical phenomenon.²¹

   

  • Mechanism of Rusting of Iron.
  • Methods of Prevention (e.g., Sacrificial protection, Galvanization).