
55-11Electrochemical Composition Measurement
To calculate the potential of a hydrogen electrode, which is strictly speaking the dierence between
the potential of the electrode and that of the solution, one has to consider the electrochemical potentials
of the respective phases. e chemical potential of gases is usually expressed in terms of the pressure p
in
stead
of th
e
mo
lar
co
ncentration
c. Du
e
to th
e
el
ementary
re
lationship
pV
= nRT
fo
r
id
eal
ga
ses,
wh
ere
V is th
e
vo
lume
of th
e
ga
s
an
d
n is th
e
am
ount
of mo
les
th
e
pr
essure,
p is pr
oportional
to th
e
mo
lar
co
n-
centration
c = n
/V
.
us,
a
ccording
to E
quation
5
5
.3
µ µ
H H
H
H
2 2
2
2
ln= +
0
0
RT
P
P
(55. ...