CHAPTER 14 GALVANIC CELLS
14.6 STANDARDELECTRODEPOTENTIALS 465
b bc
bcbcbcbcbcbcbcbcbc
bc
bc bc bc
bcbc0 0.01 0.02 0.03
0.22150.22200.2225mB=mol kg ^1E(^0) cell
=V
Figure 14.5 Ecell^0 (defined by Eq.14.5.2) as a function of HCl molality for the cell of
Fig.14.1at298:15K.aThe dashed line is a least-squares fit to a linear relation.
aData from Ref. [ 73 ] withfH
2 set equal topH 2 and the parameteraset equal to4:3^10
(^10) m.
individual cell reaction of interest. Instead, we can calculateEcell, eqfrom standard electrode
potentials.
By convention, standard electrode potentials use a standard hydrogen electrode as a
reference electrode. Astandard hydrogen electrodeis a hydrogen electrode, such as the
electrode shown at the left in Fig.14.1, in which the species H 2 (g) and HC(aq) are in their
standard states. Since these arehypotheticalgas and solute standard states, the standard
hydrogen electrode is a hypothetical electrode—not one we can actually construct in the
laboratory.
Astandard electrode potentialEis defined as the standard cell potential of a cell
with a hydrogen electrode at the left and the electrode of interest at the right. For example,
the cell in Fig.14.1with cell diagram
Pt H 2 .g/ HCl.aq/ AgCl.s/ Ag
has a hydrogen electrode at the left and a silver–silver chloride electrode at the right. The
standard electrode potential of the silver–silver chloride electrode, therefore, is equal to the
standard cell potential of this cell.
Since a cell with hydrogen electrodes at both the left and right has a standard cell poten-
tial of zero, the standard electrode potential of the hydrogen electrode iszeroat all temper-
atures. The standard electrode potential of any other electrode is nonzero and is a function
only of temperature.
Consider the following three cells constructed from various combinations of three dif-
ferent electrodes: a hydrogen electrode, and two electrodes denoted L and R.
Cell 1 has electrode L at the left and electrode R at the right.
Cell 2 has the hydrogen electrode at the left and electrode L at the right; its standard
cell potential is the standard electrode potentialELof electrode L.