CHAPTER 14 GALVANIC CELLS
14.5 EVALUATION OF THESTANDARDCELLPOTENTIAL 464
which yields the same value ofEcell, eqfor given cell conditions as Eq.14.4.5. This
value must of course be unchanged, because physically the cell is the same no matter
how we write its cell reaction, and measurable physical quantities such asEcell, eqare
unaffected. However, molar reaction quantities such asÅrGandÅrGdodepend on
how we write the cell reaction, because they are changes per extent of reaction.
14.5 Evaluation of the Standard Cell Potential
As we have seen, the value of the standard cell potentialEcell, eq of a cell reaction has useful
thermodynamic applications. The value ofEcell, eqfor a given cell reaction depends only on
temperature. To evaluate it, we can extrapolate an appropriate function to infinite dilution
where ionic activity coefficients are unity.
To see how this procedure works, consider again the cell reaction H 2 .g/C2 AgCl.s/!
2 HC.aq/C2 Cl .aq/C2 Ag.s/. The cell potential depends on the molalitymBof the HCl
solute according to Eq.14.4.5. We can rearrange the equation to
Ecell, eq DEcell, eqC
2RT
F
ln (^) C
2RT
F
ln
mB
m