Electrochemistry Lecture Notes

Introduction to Electrochemistry

• Definition: Study of generation of electricity from energy released during spontaneous chemical reactions and using electrical energy for non-spontaneous chemical reactions.
• Applications: Metals production (e.g., sodium, magnesium), sodium hydroxide, gases (chlorine, fluorine), batteries, fuel cells, and biological signal transmission.
• Benefits: Eco-friendly, energy-efficient, and less polluting technologies.

Electrochemical Cells

• Electrochemical Cell: A device for either generating electric current from chemical action or producing chemical action via electricity.
• Types:
  • Voltaic (Galvanic) Cells: Converts chemical energy of spontaneous redox reactions to electrical energy.
  • Electrolytic Cells: Uses electrical energy to carry out non-spontaneous chemical reactions.

Voltaic Cells

• Examples: Daniel Cell (Zinc + Copper ions).
• Key Concepts:
  • Half-Cells: Metal electrode in metal ion solution.
  • Connections: Electrodes connected by wire, solutions connected by a salt bridge.
  • Electrodes: Anode (oxidation, negative), Cathode (reduction, positive).
  • Electron Flow: From anode to cathode through an external circuit.
• Equations:
  • Oxidation: Anode reaction.
  • Reduction: Cathode reaction.
  • EMF Calculation: EMF = E_{ ext{right}} - E_{ ext{left}}

Standard Electrode Potentials

• Defined for unity concentrations.
• Reference: Standard Hydrogen Electrode (SHE) – assigned 0V.
• EMF Calculation: Combining a half cell with SHE and measuring EMF.

Nernst Equation

• To calculate non-standard cell potentials: E = E^{ heta} - (RT/nF) lnQ
• Practical Usage: pH meters, measuring solubility, equilibrium constants.

Conductivity

• Key Terms:
  • Resistance (R): Opposition to electricity flow, measured in ohms.
  • Conductance (G): Inverse of resistance, measured in Siemens (S).
  • Resistivity (ρ): Proportionality constant, in ohm meters.
  • Conductivity (κ): Reciprocal of resistivity, measured in S/m.
  • Types of Materials:
    • Conductors: High conductivity (metals, graphite).
    • Insulators: Low conductivity (ceramics, glass).
    • Semiconductors: Intermediate conductivity.
    • Superconductors: Zero resistivity at low temperatures.

Electrolysis

• Process: Using electrical energy to drive non-spontaneous chemical reactions.
• Examples: Electrolytic cells, refining metals.
• Faraday's Laws:
  1. Mass of deposited element ∝ charge passed.
  2. Different substances produced ∝ their equivalent masses.
• Calculations: Using charge (Q = I * t) and Faraday's constant (F = 96,487 C/mol).
• Applications: Refining metals, electroplating.

Corrosion

• Process: Oxidation of metals by environmental oxygen and water.
• Example: Rusting of iron.
• Prevention: Paint coatings, galvanization (Zn), cathodic protection.
• Cathodic Protection: Using a more easily oxidized metal (e.g., Zn, Mg) to protect another metal (e.g., steel).

Summary

• Electrochemical Processes: Integral to various industries and biological systems.
• Cell Potentials: Can be calculated under various conditions using standard reduction potentials and the Nernst equation.
• Electrical Conductivity: Understanding of resistivity and conductivity essential for practical applications.
• Electrolysis: Faraday's laws provide a framework for quantitative predictions of electrochemical reactions.
• Corrosion Protection: Essential for maintaining infrastructure and efficiency.