1. Electrochemistry G = wmax w = - Pext V w = - n F  Mechanical work
Electrical work
n =
# moles e-
F =
charge on 1 mol e-
 =
electrical potential

2. Electrochemistry electrons reduction oxidation L E O ose lectronsG E R
ain
lectrons
eduction
Ger

3. Electrochemistry silver Ag(s) Ag+(aq) aluminum Al(s) Al3+(aq) Ag(s) 
77 kJ mol-1 of
Al(s) 
Al3+(aq)
+ 3e-
Gof =
-481 kJ mol-1
these are reactions
a) oxidation
b) reduction

4. Ag(s)  Ag+(aq) + e-
Gof = 77 kJ mol-1
Al(s)  Al3+(aq) + 3e-
Gof = -481 kJ mol-1
Al(s)  Al3+(aq) + 3e-
Gof = kJ mol-1
3( )
Ag+(aq) + e-  Ag(s)
Go = kJ mol-1
3( )
__________________ ________________
3Ag+
+ Al 
3Ag +
Al3+
Go =
-712 kJ/mol
spontaneous

5. anode cathode 1 mol Al3+ + 1 molecule Al3+ 3 mol NO3-
Al  Al3+ + 3e-
Ag+ + e-  Ag
a) oxidation
b) reduction
reduction
3e-
 Cl-
K+ Al Ag
anode
cathode
1M Al(NO3)3
1M AgNO3
1 mol Al3+ +
1 molecule Al3+
3 mol NO3-
3Ag++ Al  Al3+ + 3Ag

6. anode cathode Al(s)  Al3+(1 M) Ag+(1 M) Ag(s)   Al Ag 1M Al(NO3)3
 Cl-
K+ Al Ag
anode
cathode
1M Al(NO3)3
1M AgNO3
Ag+ +e-  Ag
Al  Al3+ + 3e-
reduction
oxidation
Al(s) 
Al3+(1 M)
Ag+(1 M)
Ag(s)  

7. Reduction Potential Al(s) Al3+(aq) (1M) Ag+(aq) (1M) Ag(s)
Al(s)  Al3+ + 3e-
Ag+ + e-  Ag
3Ag+ + Al  3Ag + Al3+
Go = -712 kJ/mol
wmax =
-n F o
Go =
wmax
standard reduction potential
o =
standard =
1M, 1 atm
reduction potential =
tendency to gain e-

8. half-reaction o (V) F2 + 2e-  2F- 2.87 Ag+ + e-  Ag 0.80
spontaneous reduction
Ag+ + e-  Ag
0.80
Cu2+ + 2e-  Cu
0.34
Standard Hydrogen
electrode
2H+ + 2e-  H
o = 0
(SHE)
Sn2+ + 2e-  Sn
Al3+ + 3e-  Al
spontaneous oxidation
Li+ + e-  Li
a) oxidizing
b) reducing
F2 is spontaneously
reduced
F2 is an agent
Li is spontaneously
oxidized
Li is a agent
reducing

9. o is intensive _____________ ____ half-reaction o (V)
F2 + 2e-  2F
Ag+ + e-  Ag 0.80
Cu2+ + 2e-  Cu 0.34
2H+ + 2e-  H
Sn2+ + 2e- Sn
Al3+ + 3e-  Al
Li+ + e-  Li
o is intensive a) b)
Al half-cell and Ag half-cell
o (V)
reduction reaction:
3( )
Ag+ + e-  Ag
0.80
oxidation reaction:
_____________ ____
Al  Al3+ + 3e-
1.66 
ocell =
3Ag+
+Al
3Ag
+Al3+
2.46 V

10. ocell ocell = ored - oox Ag+ (aq) + e-  Ag(s) o = 0.80 V
Al3+ (aq) + 3e- Al(s)
o = V
ocell =
0.80
- (-1.66) =
2.46 V
spontaneous
ocell > 0
voltaic or galvanic cell
ocell < 0
electrolytic cell
non-spontaneous

11. Electrochemical work Go = wmax = - n F o 3Ag+ + Al  3Ag + Al3+
ocell = 2.46 V
Go = wmax = - n F o
n = mol of e-
F = faraday = 96,500 C / mol e-
o = standard reduction potential V (J/C)
Go =
-(3 mol e-)
(96,500 C/mol e-)
(2.46V)
= CV
= J
= -712 kJ

12. Balancing redox reactions
Cr2O72- (aq) 
Cr3+ (aq)
e-+ 6
H++ 14
Cr2O72-  Cr3+ 2
+ H2O 7
balance Cr
balance O
add H2O
balance H
add H+
balance charge
add e-

13. Cr2O H+ + 6 e-  2 Cr H2O
oxidation or reduction
oxidation state of Cr
Cr2O72- 6+
Cr3+ 3+
O = 2-
Cr has been
reduced
Cr is an agent
oxidizing

14. oxidation or reduction
Cr2O H+ + 6 e-  2 Cr H2O
oxidation or reduction
GER
gain e- reduction
need oxidation reaction
2H+ (aq)  H2(g)
balance charge with e-
H2(g)  2H+ (aq) + 2e-
2H+ + 2e- H2(g) 3 ( )
another reduction reaction