In: Chemistry
Consider the cell described below at 251 K:
Pb | Pb2+ (1.47 M) || Fe3+ (2.11 M) | Fe
Given the standard reduction potentials found on the sheet attached to the exam, calculate the cell potential after the reaction has operated long enough for the [Fe3+] to have changed by 1.078 M
Cathode (Reduction)
Fe3+ + 3e-
Fe
E° = - 0.036 V
Anode (Oxidation)
Pb Pb2+
+ 2e- E° = +
0.13 V
Net reaction
2Fe3+ + 3Pb 3Pb2+
+ 2Fe E°cell = + 0.094 V
Constructing the ICF table,
2Fe3+ |
3Pb |
3Pb2+ |
2Fe |
||
I |
2.11 M |
1.47 M |
|||
C |
-2x |
+3x |
|||
F |
2.11 - 2x |
1.47 + 3x |
Here, 2x = 1.078,
Therefore, x = 0.539
Therefore,
2Fe3+ |
3Pb |
3Pb2+ |
2Fe |
||
I |
2.11 M |
1.47 M |
|||
C |
-1.078 M |
+1.617 M |
|||
F |
1.032 M |
3.087 M |
Ecell = Eocell – (RT/nF)ln[Pb2+]3/[Fe3+]2
Ecell = 0.094 – (8.314 x 251/6 x 96500)ln[3.087]3/[1.032]2
Ecell = 0.0820 V