Download CHEMICAL REACTIONS Chapter 4

Redox
Reactions:
HALF
REACTIONS
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Electrochemical Reactions
REACTIONS
REDOX
REACTIONS
Day 1: Using
Oxidation numbers
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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
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LEO says GER
Lose electrons: OXIDATION
Gain electrons: REDUCTION
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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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Assigning
oxidation
numbers
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Copper + Silver Ion
HALF- REACTIONS
Cu(s) + 2 Ag+(aq) ---> Cu2+(aq) + 2 Ag(s)
Oxidized?
Cu(s) ---> Cu2+(aq)
Reduced?
2 Ag+(aq) ---> 2 Ag(s)
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Balancing Equations
Cu + Ag+ ----> Cu2+ + Ag
Balance BOTH mass and CHARGE
Step 1: Divide into half-reactions:
oxidation and reduction.
Ox
Red
Cu ---> Cu2+
Ag+ ---> Ag
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Balancing Equations
1. Balance each for mass (coefficients).
Already done in this case.
2. Balance each half-reaction for charge
Ox Cu ---> Cu2+ + 2e(Oxidation electrons OUT: Product)
Red
Ag+ + e- ---> Ag
(Reduction electrons IN: Reactant)
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Balancing Equations
3 Multiply each half-reaction so the electrons
lost equal the number gained
Cu ---> Cu2+ + 2e2 Ag+ + 2 e- ---> 2 Ag
Add the two half reactions to the overall
equation.
Cu + 2 Ag+
---> Cu2+ + 2Ag
balanced for BOTH charge and mass.
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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
Redox Equations
2 Al(s) + 3 Cu2+(aq) --> 2 Al3+(aq) + 3 Cu(s)
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Recognizing a Redox Reaction
2 Al(s) + 3 Cu2+(aq) --> 2 Al3+(aq) + 3 Cu(s)
Al is OXIDIZED
Al(s) -->
3+
Al (aq)
+3
e
Al Ox. # increases (more positive):
loses
e :
Oxidation
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Recognizing a Redox Reaction
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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
Recognizing a Redox Reaction
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2 half-reactions add up to give the
overall reaction
2 Al(s) --> 2 Al3+(aq) + 6 e3 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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“REDOX on Wheels”: Automobiles
D8 C13
Ready for more
complex reactions?
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No!
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