Electrolytic Cells

1
Electrolytic Cells
2
Cells and Spontaneity
electrochemical
Products

• Reactants

electrolytic
?E?cell Cell Type Spontaneity


     
     
Electrochemical
gt 0 (ve)
Yes
lt 0 (- ve)
Electrolytic
No
at equilibrium
0
or complete
3
Electrolytic cells, ?E? lt 0

• requires external source of e- to force the e-
  transfer within the cell.
• e- are forced from the anode and pushed to the
  cathode by the battery.
• rxn is then the reverse of the spontaneous rxn.
• used to electroplate and to produce pure metals.

4
eg. KI solution and battery

• Anode (ox) Eoº (V)
• 2 I- ? I2 2 e- - 0.54
• 2 H2O ? O2 4 e- 4 H - 1.23
• Cathode (red) Erº (V)
• K e- ? K - 2.71
• 2 H2O 2 e- ? H2 2 OH- - 0.83

Most ve
Most ve
2 H2O 2 I- ? I2 H2 2OH- ?E?cell - 1.37 V
? non-spontaneous, needs battery
5
Cell Shorthand Notation
C(s) KI(aq) C(s)

• e- from the anode (-ve) terminal of the BATTERY
  reduce the H2O

• e- from the I- flow to the cathode (ve) terminal
  of the battery to complete the circuit.

• forms I2 and H2 from aqueous soln!

6
(No Transcript)
7
eg. Given the following molten system, AgCl,
predict the products at each electrode. Assume
inert electrodes and sufficient voltage to cause
a reaction to take place. Consider all possible
rxns. 
OA
Ag (0.80)
Ag1
Cl1-
SOA
SRA
RA
Cl2 (-1.36)

• Cl2 is produced at the anode, Ag at the cathode.

AgCl ? Ag1 Cl1-
an Cl1- ? ½ Cl2 e- E
-1.36 V
cat Ag1 e- ? Ag E
0.80 V
Ag1 Cl1- ? Ag ½ Cl2 E
-0.56 V
8
eg. Given the following 1.00 M solution of ZnI2
at 25C, predict the anode and cathode half cell
reactions. What is the minimum voltage required
for each cell to operate?
H2 (-0.83)
OA
Zn (-0.76)
SOA
I1-
H2O
Zn2
O2 (-1.23)
SRA
I2 (-0.54)
RA
Ecell -0.76 -0.54 V -1.30 V
? 1.30 V are needed.