Handbook of Solvents - George Wypych - ChemTech - Ventech!

9.4 Mixed solvent influence on the chemical equilibrium 529
nent dependent on the 1/ε values (i.e., it is a linear correlation between lnK (univ) and 1/ε magnitudes).
The vacuum component of energy of the [9.45] process can be obtained by the assumption
of hypothetical media with ε→∞and 1/ε→0:
( )
ΔG RTlnK v ( univ )
= 1/ ε →0
[9.54]
For binary solvents formed by solvation (active component A and indifferent component
B) analysis of equation [9.52a] demonstrates that there is also a linear correlation between
lnK and 1/ε. Such mixed solvents are proposed to be called as conventionally
universal.
To analyze the solvent effect on the process [9.45], it is often convenient to represent
the temperature and permittivity dependencies of lnK in approximated form:
2
( 10 11 12 )
2
ln K = a + a / T + a / T + �+ a + a / T + a / T + � / ε+
+ a + a
00 01 02
2 2
( 20 21 / T a22 / T ) / ε
i= m
j= n
∑
+ + � + �=
=
i 0
j= o
aij
ε T
j i
[9.55]
For the universal and conventionally-universal media, this dependence described by
the equation can be represented in the form
( univ )
ln K = a + a / T + a / ε+ a / ε T
[9.56]
00 01 10 11
9.4.2 MIXED SOLVENT EFFECT ON THE POSITION OF EQUILIBRIUM OF
HOMOMOLECULAR ASSOCIATION PROCESS
All questions this part deals with are considered based on the example of a special and
wide-studied type of homomolecular association process, namely, monomer-dimer equilibrium:
2E ↔ E 2
[9.57]
For this process, equation [9.52] can be presented in the form:
[ ( ) ]
2 − βsolv E ε
(cov)
(cov)
lnKdim = ΔGdim + ΔGsolv, E − 2ΔGsolv, E + β
2 solv, E 2
, / / RT [9.58]
where:
β value at the 1/ε is calculated in accordance with the following equation
el
3
ΔGd-d =−120 6 rd-d kJ / mol
2
. μ /
μ dipole moment
Because of the electrostatic component of process [9.57], the free energy is conditioned by
dipole-dipole interactions such as dimer-solvent and monomer-solvent.
In mixed solvent, CCl4-C6H5Cl, universal relation to acetic acid (because the mixed
solvent components do not enter into specific solvation with the acid), the dimerization constant
dependence on the temperature and permittivity in accordance with [9.52.a] and [9.56]
is described by equation: 19