14.2b Cell Potentials
Reduction Potential
Cell Potential

 cell -- standard cell potential

max. electrical potential difference of a standard
cell
difference between the cathode and anode
energy
driving force on electron to move them through
the wire
also called electromotive force (emf)
units are Volts (V)




o
 1 V = 1 J/coulombs of charge
An Electrochemical Process Involves Electron Transfer at the
Interface Between the Electrode and the Solution
Digital Voltmeters
Cell potential con’t



or -- standard reduction potential
ability of a standard half-cell to attract
electrons (reduction)
the half-cell with the more positive red.
potential gains eo
E cell
o
=E
o
r
cathode
- E
r
anode
Standard Reduction Potentials

we assign  r values to each half-reactions
o
we can find the total cell by taking the difference
between the reduction potentials for the two halfreactions
 Rules

 do not change the sign of  r if you flip the half-rxtn
o
 do not multiply the  r by an integer used to balance the
electrons
o
 If ocell is positive the net rxtn is spontaneous (therefor
voltaic/galvanic)
Standard Reduction Potentials

° values for reduction half-reactions with all
solutions having 1 M conc and all gases 1 atm
Standard Hydrogen Electrode

used as reference half-cell to determine all other
o
 r values
 Pt electrode in contact with 1 M H+ and H2(g) at 1
atm
assigned an  r of zero
 can calculate others by pairing with this and
measuring total cell
o

 2H+(aq)
+
2e-(aq)
 H2(g)
r
o
= 0.00 V
Standard Hydrogen Electrode
Example
Using a cadium-zinc cell and given cell notation, label
electrodes & determine cell potential.
Cd(s) | Cd2+(aq) || Zn2+(aq) | Zn(s)
a) Cd(s) | Cd2+(aq) || Zn2+(aq) | Zn(s)
cathode
o
b) E
anode
o
cell
=E
r
cathode
-
o
Er
anode
(from data booklet, red. potential table)
= (-0.40V) - (-0.76V)
o
E
cell
= + 0.36 V (spont/voltaic)
Homework
Textbook p631 #10,11
P633 #12,13,14
LSM 14.2 F & G