Electrochemistry Overview

Key Topics Covered:

• Voltaic cell operation
• Balancing equations under acidic and basic conditions
• Identifying oxidizing and reducing agents
• Calculating cell potential under standard and non-standard conditions
• Calculating Gibbs Free Energy (ΔG) and equilibrium constant (K)
• Electrolysis problems and stoichiometry
• Calculating current or mass deposited on the cathode

Voltaic Cell Operation

• Voltaic (Galvanic) Cell: Produces energy; spontaneous reactions with positive cell potential.
• Electrolytic Cell: Requires energy input; can have positive or negative cell potential.
• Example: Zinc electrode (anode) and copper electrode (cathode).

Standard Reduction Potentials

• Zinc: -0.76 V
• Copper: +0.34 V

Cell Reaction

• Spontaneity: Cell potential must be positive for a spontaneous reaction.
• Electrode Processes:
  • Anode (Oxidation): Zinc loses electrons (Zn → Zn²⁺ + 2e⁻).
  • Cathode (Reduction): Copper ions gain electrons (Cu²⁺ + 2e⁻ → Cu).
  • Electron Flow: From anode to cathode.

Salt Bridge

• Maintains charge balance by allowing cations and anions to move between the solutions.
• Cations: Move towards cathode.
• Anions: Move towards anode.

Calculating Cell Potential

• Standard Conditions: Concentration of ions is 1 M, cell potential is calculated using E° = 0.76 V + 0.34 V = 1.1 V.
• Non-standard Conditions: Use Nernst equation to calculate cell potential when ion concentrations differ.

Gibbs Free Energy (ΔG) and Equilibrium Constant (K)

• ΔG Calculation: ΔG = -nFE, where n = number of moles of electrons, F = Faraday's constant (96485 C/mol e⁻).
• Relation to Cell Potential: Positive cell potential implies negative ΔG (spontaneous reaction).
• Equilibrium Constant (K): Derived from ΔG = -RT ln(K); large K indicates product-favored equilibrium.

Electrolysis and Stoichiometry

• Electrolysis Problems: Calculate mass or volume changes during electrolysis using stoichiometry and Faraday's laws.
• Examples:
  • Calculate mass of copper deposited with given current and time.
  • Determine time required to deposit a given mass at a specified current.

Additional Concepts

• Identifying Agents:
  • Reducing Agent: Substance that loses electrons (is oxidized).
  • Oxidizing Agent: Substance that gains electrons (is reduced).
• Balancing Reactions:
  • Under acidic conditions: Add H⁺ and H₂O.
  • Under basic conditions: Add OH⁻ to both sides, balance charges and atoms.
• Cell Notation: Write cell notation showing oxidation and reduction half-reactions, phases, and electrodes.

Summary

• Understanding electrochemistry requires knowledge of cell types, calculation methods for potentials and free energy, and the ability to balance reactions under various conditions.
• Electrochemistry involves both theoretical calculations and practical applications like electroplating and electrolysis.