Handbook of Solvents - George Wypych - ChemTech - Ventech!

534 Y. Y. Fialkov, V. L. Chumak
Only when A is a solvate-active component in the mixed solvent A-B, in the general
case, both A and B initial components undergo specific solvation:
E + A↔ EA
[9.69]
F + A↔ FA
[9.70]
where:
EA, FA solvated molecules by the solvent (it is not necessary to take into account solvation
number for further reasoning)
Since specific solvation of the adduct EF is negligible in comparison with specific solvation
of initial components, A-B interaction in the solvent can be presented by the scheme:
EA + FA ↔ EF + 2 A
[9.71]
i.e., the heteromolecular association process in the specific medium is a resolvation process,
since both initial components change their solvative surrounding. That is why equilibrium
constants of the heteromolecular association process, calculated without consideration of
this circumstance, belong indeed to the [9.71] process but not to the process [9.68].
Let us develop a quantitative relation between equilibrium constants for the process
[9.68]
[ ] [ ][ ]
K = EF / E F
[9.72]
EF
and for the resolvation process [9.71]
[ ] [ ][ ]
K = EF / EA FA
[9.73]
us
Concentration of the solvate active solvent or the solvate active component A of
mixed solvent in dilute solution is higher than the initial concentration of equilibrium components
[E] 0 and [F] 0. Then activity of equilibrium components is equal to their concentrations.
Then equations of material balance for components A and B can be set down as
[ E] [ E] [ EF] [ EA]
0
= + + [9.74]
[] F [] F [ EF] [ FA]
0
= + + [9.75]
Hence equilibrium constants of the process [9.69, 9.70] are presented by expressions
( 0 )
( )
[ ] / [ ] [ ] / [ ] [ ] [ ]
K = EA E = EA E − EF − EA
EA
[ ] / [ ] [ ] / [ ] [ ] [ ]
K = FA F = FA F − EF − FA
FA
Definition [9.72] is presented in the form
[ ] [ ] [ ] [ ]
/
0
( ) ( [] [ ][ ] )
K = EF E − EF − EA F − EF − FA
EF
and re-solvation constant
0 0
[9.76]
[9.77]
[9.78]