Electrochemistry Notes
Objectives
- Describe an electrochemical cell and differentiate between galvanic and electrolytic cells.
- Apply Nernst equation for calculating the emf of galvanic cells and define standard potential of the cell.
- Derive relation between standard potential of the cell, Gibbs energy of cell reaction, and its equilibrium constant.
- Define resistivity (ρ), conductivity (κ), and molar conductivity (Λ) of ionic solutions.
- Differentiate between ionic (electrolytic) and electronic conductivity.
- Describe the method for measurement of conductivity of electrolytic solutions and calculation of their molar conductivity.
- Justify the variation of conductivity and molar conductivity of solutions with change in their concentration.
- Define 1°m (molar conductivity at zero concentration or infinite dilution).
- Enunciate Kohlrausch law and learn its applications.
- Understand quantitative aspects of electrolysis.
- Describe the construction of some primary and secondary batteries and fuel cells.
- Explain corrosion as an electrochemical process.
Key Concepts
Electrochemical Cells
- Galvanic Cell: Converts chemical energy into electrical energy.
- Electrolytic Cell: Uses electrical energy to drive a non-spontaneous chemical reaction.
Conductivity and Molar Conductivity
- Conductivity (κ): Measured in S m⁻¹; depends on the concentration of the electrolyte, nature of solvent, and temperature.
- Molar Conductivity (Λ): Defined as Λ = κ/c, where c is the concentration.
- Increases with dilution for weak electrolytes.
- Decreases with dilution for strong electrolytes.
Faraday's Laws of Electrolysis
- First Law: The amount of chemical reaction at an electrode is proportional to the quantity of electricity passed.
- Second Law: The amounts of different substances liberated by the same quantity of electricity are proportional to their chemical equivalent weights.
Important Formulas
| Formula | Description |
|---|
| R = ρ(l/A) | Resistance in terms of resistivity, length, and area of cross-section. |
| κ = 1/ρ | Conductivity is the inverse of resistivity. |
| Λ = κ/c | Molar conductivity defined in relation to conductivity and concentration. |
| E°cell = E°cathode - E°anode | Standard potential of the cell. |
| ΔG° = -nFE° | Gibbs energy related to cell potential. |
Examples
- Example 2.7: Calculate Aₘ for CaCl₂ and MgSO₄ using Kohlrausch's law.
- Example 2.8: Calculate A° for HAc using known molar conductivities.
Applications
- Batteries and Fuel Cells: Convert chemical energy into electrical energy; used in various devices.
- Corrosion: An electrochemical phenomenon affecting metals.
- Hydrogen Economy: Hydrogen as a renewable energy source through electrochemical processes.
Summary
Electrochemistry involves the study of chemical reactions that produce electrical energy and the use of electrical energy to drive chemical reactions. Key concepts include the types of electrochemical cells, conductivity, molar conductivity, and Faraday's laws of electrolysis.
