Key concepts: Definitions and terminology

1. Electrolysis vs. Electrochemical Cells

• Electrolysis: A process where electrical energy is used to drive a chemical reaction.
• Electrolytic cell: A system in which electrical energy forces a chemical change (e.g., electrolysis of water).
• Galvanic (Voltaic) cell: A system where a spontaneous chemical reaction produces electrical energy.

2. Oxidation & Reduction (Redox Reactions)

• Oxidation: The loss of electrons by a substance (atom, molecule, or ion).
  • Mnemonic: LEO – Loss of Electrons is Oxidation.
  • A substance that undergoes oxidation is called a reducing agent.
  • The oxidation number increases.
• Reduction: The gain of electrons by a substance (atom, molecule, or ion).
  • Mnemonic: GER – Gain of Electrons is Reduction.
  • A substance that undergoes reduction is called an oxidising agent.
  • The oxidation number decreases.

3. Electrodes & Their Roles

• Anode ($-$ in galvanic cell, $+$ in electrolytic cell): Where oxidation takes place.
  • Mnemonic: AN OX – Anode is Oxidation.
• Cathode ($+$ in galvanic cell, $-$ in electrolytic cell): Where reduction takes place.
  • Mnemonic: RED CAT $–$ Reduction at Cathode.

• Electrolyte: A solution or molten substance that conducts electricity by allowing ion movement.

4. Summary of Cell Types

Feature	Galvanic (Voltaic) Cell	Electrolytic Cell
Energy conversion	Chemical → Electrical	Electrical → Chemical
Spontaneity	Spontaneous reaction	Non-spontaneous reaction
Anode charge	Negative $(-)$	Positive $(+)$
Cathode charge	Positive $(+)$	Negative $(-)$