Mastering Half Reactions and Redox Reactions

Study Notes

Half Reactions in Redox Reactions

A half reaction is either the oxidation or reduction reaction component of a redox reaction.
Half reactions are used to describe what occurs in an electrochemical cell, such as a Galvanic cell battery.

Features of Half Reactions

Half reactions can be written to describe both the metal undergoing oxidation (anode) and the metal undergoing reduction (cathode).
Half reactions are used as a method of balancing redox reactions.
For oxidation-reduction reactions in acidic conditions, H+ ions are added to balance the hydrogen ions in the half reaction.
For oxidation-reduction reactions in basic conditions, OH− ions are added to balance the H+ ions in the half reactions.

Example: Zn and Cu Galvanic Cell

The overall reaction is: Zn (s) + CuSO4 (aq) → ZnSO4 (aq) + Cu (s)
At the Zn anode, oxidation takes place (the metal loses electrons): Zn (s) → Zn2+ + 2e-
At the Cu cathode, reduction takes place (electrons are accepted): Cu2+ + 2e- → Cu (s)

Example: Oxidation of Magnesium

The overall reaction is: 2Mg (s) + O2 (g) → 2MgO (s)
Magnesium loses 2 electrons to form Mg2+: 2Mg (s) → 2Mg2+ + 4e-
Oxygen gains 4 electrons to form O2-: O2 (g) + 4e- → 2O2-
The overall reaction is the sum of both half reactions: 2Mg (s) + O2 (g) → 2Mg2+ + 2O2-

Half-Reaction Balancing Method

Consider the reaction: Cl2 + 2Fe2+ → 2Cl- + 2Fe3+
Iron changes oxidation state from +2 to +3, and chlorine from 0 to -1.
There are two half reactions occurring: oxidation and reduction.

Description

Test your knowledge of half reactions and redox reactions in chemistry with this quiz. Explore the concept of oxidation and reduction and learn how to identify and balance half reactions. Perfect your understanding of electrochemical cells and their role in battery operation.