1 redox reactions : half reactions. 2 redox reactions day 1: using oxidation numbers electrochemical...
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11
Redox Redox ReactionsReactions
::
HALF HALF REACTIONSREACTIONS
2
REDOX REACTIONS
REDOX REACTIONS
Day 1: UsingDay 1: UsingOxidation numbers
Electrochemical ReactionsElectrochemical Reactions
REACTIONSREACTIONS
33Terminology; Redox Reactions
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
• 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
44
LEO says GER
Lose electrons: OXIDATION
Gain electrons: REDUCTION
5
Redox reactions are characterized byRedox reactions are characterized by ELECTRON TRANSFERELECTRON TRANSFER between an between an electron donor and electron acceptor.electron donor and electron acceptor.
Transfer leads to— Transfer leads to—
1. 1. increase in oxidation numberincrease in oxidation number of some element = of some element = OXIDATIONOXIDATION
2.2. decrease in oxidation numberdecrease in oxidation number of some element = of some element = REDUCTIONREDUCTION
REDOX REACTIONSREDOX REACTIONSREDOX REACTIONSREDOX REACTIONS
66
Assigning oxidation numbers
88
Copper + Silver IonCopper + Silver Ion
99
HALF- REACTIONSHALF- REACTIONS
Cu(s) + 2 Ag+(aq) ---> Cu2+(aq) + 2 Ag(s) Oxidized?
Cu(s) ---> Cu2+(aq)
Reduced?
2 Ag+(aq) ---> 2 Ag(s)
1010Balancing Balancing EquationsEquations
Balance BOTH mass and CHARGE
Cu + Ag+ ----> Cu2+ + Ag
Step 1:: Divide into half-reactions:
oxidation and reduction.
Ox Cu ---> Cu2+
Red Ag+ ---> Ag
1111Balancing Balancing EquationsEquations
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)
1212Balancing Balancing EquationsEquations
3 Multiply each half-reaction so the electrons lost equal the number gained
Cu ---> Cu2+ + 2e- 2 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.
1313
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
1414
2 Al(s) + 3 Cu2+(aq) --> 2 Al3+(aq) + 3 Cu(s)
Redox Redox EquationsEquations
1515
Recognizing a Redox Recognizing a Redox ReactionReaction
Recognizing a Redox Recognizing a Redox ReactionReaction
2 Al(s) + 3 Cu2+(aq) --> 2 Al3+(aq) + 3 Cu(s)
Al is OXIDIZED Al is OXIDIZED
Al(s) --> Al3+(aq) + 3 e-
Al Ox. # increases (Al Ox. # increases (more positive):):
loses e- : Oxidation
1616Recognizing a Redox Recognizing a Redox ReactionReaction
Recognizing a Redox Recognizing a Redox ReactionReaction
2Al(s) + 3Cu2+(aq) ’ 2Al3+(aq) + 3Cu(s)
Cu is REDUCED Cu is REDUCED
Cu2+(aq) + 2 e- ’ Cu(s)
•Ox. # of Cu decreases (more neg.)
• gaining electrons Reduction
1717Recognizing a Redox Recognizing a Redox ReactionReaction
Recognizing a Redox Recognizing a Redox ReactionReaction
2 half-reactions add up to give the overall reaction
2 Al(s) --> 2 Al3+(aq) + 6 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.
1818
1919
“REDOX on Wheels”: Automobiles
D8 C13
2121Ready for more complex reactions??
No!No!
2222
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