Redox Half Reactions

Core Concept

A redox reaction can be split into two half-reactions: one for oxidation and one for reduction.

  • Oxidation Half-Reaction: Shows the loss of electrons (LEO: Loss of Electrons is Oxidation).

  • Reduction Half-Reaction: Shows the gain of electrons (GER: Gain of Electrons is Reduction).

  • Redox half-reactions break a redox reaction into oxidation and reduction components.

  • Electrons lost in oxidation must equal electrons gained in reduction.

  • Use systematic steps to balance redox reactions in acidic or basic solutions.

  • Mastering half-reactions is essential for understanding electrochemical cells and redox processes.

Test Yourself

Assorted Multiple Choice
A constant current is passed through an electrolytic cell for 45.0 minutes, delivering a total charge of 8,100 Coulombs. How many moles of electrons were transferred during this process? (Faraday's constant = 96,485 C/mol e⁻)

Podcast Episode

Episode

Introduction to Redox

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Student Guide Teacher Guide

Key Terms

Oxidation:

  • Occurs when a species loses electrons.

  • The oxidation state increases.

  • Example: Zn (s)→Zn2+(aq)+2e−\text{Zn (s)} \rightarrow \text{Zn}^{2+} (aq) + 2e^-Zn (s)→Zn2+(aq)+2e−

Reduction:

  • Occurs when a species gains electrons.

  • The oxidation state decreases.

  • Example: Cu2+(aq)+2e−→Cu (s)\text{Cu}^{2+} (aq) + 2e^- \rightarrow \text{Cu (s)}Cu2+(aq)+2e−→Cu (s)

Electrons:

  • Electrons lost in oxidation must equal electrons gained in reduction.

Steps to Write Redox Half-Reactions

  1. Identify the Redox Reaction:

    • Determine which species is oxidized and which is reduced.

  2. Write the Oxidation Half-Reaction:

    • Show the species losing electrons and balance for mass and charge.

  3. Write the Reduction Half-Reaction:

    • Show the species gaining electrons and balance for mass and charge.

  4. Balance the Electrons:

    • Ensure the number of electrons lost in oxidation equals the number gained in reduction.

  5. Combine the Half-Reactions:

    • Add the half-reactions to get the overall balanced redox reaction.

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