Cell EMF

1
Cell EMF
Eocell Eored(cathode) - Eored(anode)
Example Zn Cu2 ? Zn2 Cu E0cell 0.34
V - (-0.76 V) 1.10 V
2
A voltaic cell is based on two half-reactions
Cd2/Cd Sn2/Sn Which half-reaction takes
place at the cathode? Which half-reaction takes
place at the anode? What is the standard cell
potential?
3
A voltaic cell is based on two half-reactions
Cd2/Cd Sn2/Sn Which half-reaction takes
place at the cathode? Which half-reaction takes
place at the anode? What is the standard cell
potential?
Sn2 2e- ? Sn
Cd ? Cd2 2e-
0.267 V
4
(No Transcript)
5
Spontaneity of Redox Reactions
Eo Eored(reduction) - Eored(oxidation)
E0 () spontaneous E0 (-) nonspontaneous
6
Cu 2H ? Cu2 H2
Calculate the value of E0.
7
Cu 2H ? Cu2 H2
Calculate the value of E0.
E0 -0.34 V NOT SPONTANEOUS
8
EMF and Free-Energy Change
?G -nFE
n a positive (the of electrons
transferred) F Faradays constant. 1F
96,500 J/V-mol E EMF
9
Use the standard reduction potentials to
calculate the standard free-energy change, ??Go,
for the following reaction
4Ag O2 4H ? 4Ag 2H2O
10
Use the standard reduction potentials to
calculate the standard free-energy change, ??Go,
for the following reaction
4Ag O2 4H ? 4Ag 2H2O
?Go -(4)(96,500J/V-mol)(0.43V) - 170 kJ/mol
11
The Nernst Equation
(at 298 K)
12
Calculate the emf at 298K generated by the
following cell, when (Cr2O7-2) 2.0 M, (H)
1.0 M, (I-) 1.0 M, and (Cr3) 1.0 x 10-5 M
Cr2O7-2(aq) 14H(aq) 6I-(aq) ? 2Cr3(aq)
3I2(s) 7H20(l)
13
Calculate the emf at 298K generated by the
following cell, when (Cr2O7-2) 2.0 M, (H)
1.0 M, (I-) 1.0 M, and (Cr3) 1.0 x 10-5 M
Cr2O7-2 14H 6I- ? 2Cr3 3I2 7H20
E 0.79 V - 0.0592V/6 log(5.0 x 10-11) E
0.89 V