• The potential difference (voltage)
between the anode and cathode in a
cell is called the cell potential (E°cell).
• For any reaction that is spontaneous
E°cell will be positive.
• It is measured in volts (V). (1 V = 1
Joule/Coulomb)
Standard Cell Potentials
The cell potential at standard conditions (1
M concentration for reactants and products
and 1 atm of pressure) can be found through
this equation:
°
°
Ecell= Ered (cathode)° – Ered (anode)
Cathode or anode?!
Ered
° (cathode) has a more positive value
than the anode
A galvanic cell is based on the two standard
half-reactions:
Cd2+(aq) + 2e-  Cd(s)
Sn2+(aq) + 2e-  Sn(s)
Which half-reaction occurs at the cathode
and which occurs at the anode?
What is the standard-cell potential?
Calculate the standard E° for a cell that
employs the overall cell reaction 2 Al(s) + 3
I2(s)  2 Al3+(aq) + 6 I-(aq)
• 2.20 V
• Increasing the concentration of
reactants or decreasing the
concentration of products increases
the driving force of the reaction
resulting in a higher Ecell.
• The opposite would result in a lower
Ecell
Free Energy
• Since Gibbs free energy is the measure of
spontaneity, +Ecell corresponds to -ΔG.
ΔG = –nFE
n = number of moles (of electrons)
F = Faraday’s constant = 96,485 Coulombs per
mole of electrons
E = standard reduction potential
Use the standard reduction potentials
to calculate the standard free-energy
change ΔG and the equilibrium
constant, K, at 298 K for the reaction:
4Ag(s) + O2(g) + 4H+(aq) → 4Ag+(aq) + 2
H2O(l)