1. Balancing Redox Reactions from Half-Reactions

2. Half-Reaction
Describes the oxidation or reduction process going on in a redox reaction
2 half-reactions make ONE redox reaction
Contains “half” of a redox reaction

3. Half-Reaction Example
Cu+2(aq) e Cu (s) Reduction
Mg (s) Mg+2 (aq) e Oxidation
Total: Mg(s) Cu+2(aq) Mg+2(aq) Cu(s)

4. Methods for Balancing Redox Reactions
Inspection pp
Half-Reaction Method pp

5. What does a balanced redox reaction look like?
Electric charges are equal on both sides
Cannot be created or destroyed
The amount of each atom is equal on both sides
Matter cannot be created or destroyed

6. Balancing Procedure
Equal number of electrons in both half-reactions (oxidation and reduction)
Electrons are transferred in chemical reactions but cannot be created or destroyed ! ! !
Electrons lost = Electrons gained
(oxidation) (reduction)

7. Example 1: Reduction Cu+2(aq) + 2e-1 Cu (s)
Oxidation Mg (s) Mg+2 (aq) e-1

8. Example 2:
Oxidation: Cu (s) Cu+2(aq) + 2e -1 Reduction: Ag+1 (aq) + 1e -1 Ag (s) *When electrons do not balance, multiply one or both half- reactions when needed to balance the amount of electrons gained and lost in the reaction. **

9. Homework
P. 792 #25, Read pp
Read over lab procedure, Lab Report due tomorrow (Thursday)
Write half-reactions and balance if the reaction is redox !
Mg + 2HCl  MgCl H2
I Cl2  ICl3
NaOH + HCl  NaCl H2O
2Na H2O  2NaOH H2