Page 192 - MODERN ELECTROCHEMISTRY

130 CHAPTER 2

where is the weight fraction of NaCl in solution. needed to calculate is
given by

where and are the mole fractions of salt and solvent in the solution. Using
measurements of the velocity of sound, from Eq. (2.99), and from Eq.
(2.100), can be calculated from Eq (2.97) for different mole fractions, of
the salt.
The obtained from the slope of [cf. Eq. (2.95)] is near zero and
it is inferred that this value indicates a value of zero for the translational entropy of
the ion. A similar result was obtained for the solvated complex. Zero translational
entropy for a solvated ion is a reasonable conclusion. Thus, for most of its time, the
ion is still in a cell in the solution and only occasionally does it jump into a vacancy,
or if it shuffles about, its movement is so constrained compared with that of a gas that
it may approach zero.

2.15.13.4. S i-SCW . The entropy of solvationally coordinated water is made
up of librational (S i,lib ) and vibrational contributions. can be calculated as
follows.
The partition function of a particle, under an electric field is

where and are the moments of inertia of the water molecules about three
mutually perpendicular axes and is the ion–water interaction energy. The symbol
is the symmetry factor and is equal to 2 for water. Therefore (see physicochemical
texts)

In the case of water molecules oriented near the ion, and Eq. (2.102) becomes