Introduction to Electrochemistry and Cells

Jul 9, 2024

Electrochemistry

Interconversion of Energy

  • Electrochemistry: The mutual conversion of chemical energy and electrical energy.
  • Electrochemical Cell: A device in which this conversion occurs.
  • Two Types of Cells:
    1. Galvanic or Voltaic Cell
    2. Electrolytic Cell

Galvanic Cell vs. Electrolytic Cell

  • Galvanic (Voltaic) Cell:
    • Spontaneous redox reaction (ΔG < 0)
    • Conversion of chemical energy into electrical energy
    • Indirect redox reaction
  • Electrolytic Cell:
    • Non-spontaneous redox reaction (ΔG > 0)
    • Conversion of electrical energy into chemical energy
    • Direct redox reaction

Galvanic Cell Structure

  • Oxidation Half Cell (Anode): Negatively charged electrode.
  • Reduction Half Cell (Cathode): Positively charged electrode.
  • Salt Bridge: Completes the circuit internally and maintains the electrical neutrality of the electrolyte solution.
  • Each Half Cell: A metal electrode dipped in its electrolyte solution.

Working of Galvanic Cell

  • Zinc Electrode: Zn -> Zn²⁺ + 2e⁻ (Oxidation Half Cell)
  • Copper Electrode: Cu²⁺ + 2e⁻ -> Cu (Reduction Half Cell)
  • Overall Reaction: Zn + Cu²⁺ -> Zn²⁺ + Cu
  • Cell Representation: Zn | Zn²⁺ || Cu²⁺ | Cu

Electrode Potential

  • Definition: Potential difference between the electrode and electrolyte. Measured in volts.
  • Standard Electrode Potential: Measured at 25°C, 1 molar concentration, 1 ATM pressure.
  • EMF: Potential difference between cathode and anode (E cathode - E anode)

Nernst Equation

  • Formula: E_cell = E°_cell - (0.0591/n) log(Q)
  • **Useful for calculating EMF under non-standard conditions.

Gibbs Free Energy

  • Formula: ΔG° = -nFE°_cell
  • Negative ΔG indicates a spontaneous reaction

Conductivity and Conductance

  • Conductivity (κ): C = kA / l
  • Conductance (G): G = 1/R
  • Conductivity Formula: G_star x conductance

Conductivity of Cells

  • Effect of Dilution: Conductivity decreases while molar conductance increases.
  • Debye Huckel: λ_m^∞ = λ⁺ + λ⁻

Quantitative Analysis of Electrolysis

  • Faraday's Law: m = (E × I × t) / (n × 96500)
  • Calculating products at cathode and anode.

Preferential Discharge Theory

  • Importance of Discharge Potential
  • Anode oxidizes giving off gas while the cathode reduces easily and deposits.