Summary Redox Reaction

Redox Reactions


What is a Redox Reaction?
Redox stands for:
REDuction + OXidation
A redox reaction is a chemical reaction in which electrons are transferred
between substances.
• Oxidation = loss of electrons
• Reduction = gain of electrons

These always happen together — if one substance loses electrons,
another must gain them.


Key Definitions You Must Know

Term Definition

Oxidation Loss of electrons

Reduction Gain of electrons

Oxidising A substance that causes oxidation (it gains electrons and
agent is reduced)

Reducing A substance that causes reduction (it loses electrons and
agent is oxidised)

Oxidation A number representing the charge an atom would have if
number electrons were completely transferred



Oxidation in Terms of Oxygen and Hydrogen
Besides electrons, oxidation and reduction can also be described as:
Process Another Way to Recognise It

Oxidation Gain of oxygen

, Process Another Way to Recognise It

Oxidation Loss of hydrogen

Reduction Loss of oxygen

Reduction Gain of hydrogen
Example:
2𝑀𝑔 + 𝑂2 → 2𝑀𝑔𝑂
• Magnesium gains oxygen → oxidised
• Oxygen gains electrons → reduced

Example 1: Simple Electron Transfer (Metal + Ion Reaction)
Step 1: Write Half Equations
Oxidation: 𝑍𝑛 → 𝑍𝑛2+ + 2𝑒 −
Reduction: 𝐶𝑢2+ + 2𝑒 − → 𝐶𝑢
What’s Happening?
• Zinc loses electrons → oxidised
• Copper ion gains electrons → reduced
• Zinc is the reducing agent
• Copper ion is the oxidising agent


Example 2: Combustion Reaction
𝐶𝐻4 + 2𝑂2 → 𝐶𝑂2 + 2𝐻2 𝑂
Carbon in methane:
• Oxidation number goes from –4 → +4
• It is oxidised
Oxygen:
• Goes from 0 → –2
• It is reduced