1. Redox Reactions: HALF REACTIONS
To play the movies and simulations included, view the presentation in Slide Show Mode.

2. Electrochemical Reactions
REDOX REACTIONS
REACTIONS
Day 1: Using
Oxidation numbers

3. Terminology; Redox Reactions
OXIDATION—loss of electron(s)
increase in oxidation number.
Or called REDUCING AGENT.
REDUCTION—gain of electron(s);
decrease in oxidation number.
Or called OXIDIZING AGENT

4. Lose electrons: OXIDATION Gain electrons: REDUCTION
LEO says GER
Lose electrons: OXIDATION
Gain electrons: REDUCTION

5. REDOX REACTIONS
Redox reactions are characterized by ELECTRON TRANSFER between an electron donor and electron acceptor.
Transfer leads to—
1. increase in oxidation number of some element = OXIDATION
2. decrease in oxidation number of some element = REDUCTION

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7. Assigning oxidation numbers7

8. Copper + Silver Ion

9. Cu(s) + 2 Ag+(aq) ---> Cu2+(aq) + 2 Ag(s) Oxidized?
HALF- REACTIONS
Cu(s) Ag+(aq) ---> Cu2+(aq) Ag(s) Oxidized?
Cu(s) ---> Cu2+(aq)
Reduced?
2 Ag+(aq) ---> 2 Ag(s)

10. Balancing Equations Balance BOTH mass and CHARGE
Cu + Ag > Cu Ag
Balance BOTH mass and CHARGE
Step 1: Divide into half-reactions:
oxidation and reduction.
Ox Cu ---> Cu2+
Red Ag+ ---> Ag

11. Balancing Equations Ox Cu ---> Cu2+ + 2e- Red Ag+ + e- ---> Ag
1. Balance each for mass (coefficients).
Already done in this case.
2. Balance each half-reaction for charge
Ox Cu ---> Cu e-
(Oxidation electrons OUT: Product)
Red Ag+ + e- ---> Ag
(Reduction electrons IN: Reactant)

12. Balancing Equations 2 Ag+ + 2 e- ---> 2 Ag
3 Multiply each half-reaction so the electrons lost equal the number gained
Cu ---> Cu e-
2 Ag e- ---> 2 Ag
Add the two half reactions to the overall equation.
Cu Ag > Cu Ag
balanced for BOTH charge and mass.

13. Space Fight Identify two half reactions
ID which element reduced and which is oxidized
Why are liquid fuel preferred over gaseous?
Why use hydrogen and oxygen as fuels if solid fuels provide better propulsion?
D8 C10 13

14. 2 Al(s) + 3 Cu2+(aq) --> 2 Al3+(aq) + 3 Cu(s)
Redox Equations
2 Al(s) + 3 Cu2+(aq) --> 2 Al3+(aq) + 3 Cu(s) 14

15. Recognizing a Redox Reaction
2 Al(s) + 3 Cu2+(aq) --> 2 Al3+(aq) + 3 Cu(s)
Al is OXIDIZED
Al(s) --> Al3+(aq) + 3 e-
Al Ox. # increases (more positive):
loses e- : Oxidation

16. Recognizing a Redox Reaction
2Al(s) + 3Cu2+(aq) ’ 2Al3+(aq) + 3Cu(s)
Cu is REDUCED
Cu2+(aq) + 2 e- ’ Cu(s)
Ox. # of Cu decreases (more neg.)
gaining electrons Reduction

17. Recognizing a Redox Reaction
2 half-reactions add up to give the overall reaction
2 Al(s) --> 2 Al3+(aq) e-
3 Cu2+(aq) + 6 e- --> 3 Cu(s)
2 Al(s) + 3 Cu2+(aq) ---> 2 Al3+(aq) + 3 Cu(s)
balanced for mass and charge.

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20. “REDOX on Wheels”: Automobiles
D8 C13 20

21. Ready for more complex reactions?
No!