19.0 ELECTROCHEMISTRY

Electrochemistry is the study of the relationship between chemical reactions and electricity. It encompasses two main areas: galvanic (voltaic) cells, which use spontaneous redox reactions to generate electricity, and electrolysis, which uses electricity to drive non-spontaneous reactions. This chapter builds on earlier concepts of redox, introduces standard electrode potentials, revisits electrolysis with quantitative calculations (Faraday's laws), and explores applications like electroplating and corrosion prevention.

19.1 REDOX REACTIONS: OXIDATION NUMBERS AND ELECTRON TRANSFER

Redox reactions involve both reduction and oxidation occurring simultaneously.

• Oxidation is:
  • Loss of electrons
  • Increase in oxidation number
• Reduction is:
  • Gain of electrons
  • Decrease in oxidation number

Oxidizing agent: The species that causes oxidation by accepting electrons (itself gets reduced).
Reducing agent: The species that causes reduction by donating electrons (itself gets oxidized).

19.1.1 Oxidation Numbers (Oxidation States)

Oxidation numbers are a bookkeeping tool to track electron transfer. Rules:

1. Oxidation number of an element in its free state is 0 (e.g., Na, O₂, Cl₂).
2. For a monatomic ion, oxidation number = charge on the ion (e.g., Na⁺ = +1, Cl⁻ = -1).
3. Oxygen usual