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.