Solvent activity coefficients representative values

In this equation x, is the liquid perfume concentration, Mt the molecular weight, R the ideal gas constant, and T the absolute temperature. Equation 2 relates the liquid perfume composition, x, with the human sensory reaction of the evaporated perfume. A key factor of Equation 2 is the activity coefficient, y, because it represents the affinity of a molecule to its neighboring medium. High value of y means an increased inclination for a given substance to be released from the mixture and low value of y means a low concentration in the headspace. This means that the OV values of a particular component can change if it is diluted in different solvents or mixed with different fragrance components. 

In Equations 2, 4, and 6, ax represents thermodynamic activities based on molar concentrations Cj of the species indicated, y represents mean ionic activity coefficients, i/ha is the activity coefficient of HA(S) molecules, and the activity of water is chosen to be one in all solvents. Consequently values of K, AG°, and AS° are based on these choices regarding standard states. 

Table 5-19. Some representative values of solvent-transfer activity coefficients for anions and cations at 25 °C with water (W) as reference solvent molar concentration scale f For the corresponding Gibbs energies of transfer, see Table 2-9 in Section 2.3. 

Scientific literature shows how the experimental curves that represent the variation in the mean activity coefficients as a function of the molality (i.e., the amount of substance in mol per kilogram of solvent ), often have a minimum. Moreover, the value of the mean activity coefficient may exceed 1 (see figure 3.2). Therefore, when dealing with concentrated electrolytes, one can see how the experimental results rapidly seem to deviate from the variation laws as presented above (they all show a monotonic variation in the mean activity coefficient as a function of the molality or the concentration). 

The use of the above quantities in the selection of potential solvents for extractive distillation has to be approached with caution as the physicochemical properties of the system at infinite dilution can differ quite markedly from that at te concentration [16], where for conventional extractive distillation, the latter represents the technically relevant composition range. Since the condition at infinite dilution is one of maximum non-ideality and the value of the activity coefficient is highly concentration-dependant, selectivity values at finite concentration can be much lower than those at infinite dilution [59]. 

The solvent dependency of Katrp was also examined in terms of Kamlet-Taft parameters for 11 solvents and then extrapolated to cover catalyst activity in a total of 28 solvents, including water. The log(KATRp) values measured in this work for Cu Br/l,l,4,7,10,10-hexamethylttiethylenetetramine (HMTETA) + MBriB are plotted against values predicted by the Kamlet-Taft relationship the line representing values predicted by the Kamlet-Taft relationship is shown in Figure 8. Predicted values of Katrp for 16 organic solvents and water are also provided, based on these solvent-independent coefficients and the appropriate solvatochromic parameters. 

Lipophilicity is a molecular property expressing the relative affinity of solutes for an aqueous phase and an organic, water-immiscible solvent. As such, lipophilicity encodes most of the intermolecular forces that can take place between a solute and a solvent, and represents the affinity of a molecule for a lipophilic environment. This parameter is commonly measured by its distribution behavior in a biphasic system, described by the partition coefficient of the species X, P. Thermodynamically, is defined as a constant relating the activity of a solute in two immiscible phases at equilibrium [111,112]. By convention, P is given with the organic phase as numerator, so that a positive value for log P reflects a preference for the lipid phase ... 

There seems little doubt that in radiation induced polymerizations the reactive entity is a free cation (vinyl ethers are not susceptible to free radical or anionic polymerization). The dielectric constant of bulk isobutyl vinyl ether is low (<4) and very little solvation of cations is likely. Under these circumstances, therefore, the charge density of the active centre is likely to be a maximum and hence, also, the bimolecular rate coefficient for reaction with monomer. These data can, therefore, be regarded as a measure of the reactivity of a non-solvated or naked free ion and bear out the high reactivity predicted some years ago [110, 111]. The experimental results from initiation by stable carbonium ion salts are approximately one order of magnitude lower than those from 7-ray studies, but nevertheless still represent extremely high reactivity. In the latter work the dielectric constant of the solvent is much higher (CHjClj, e 10, 0°C) and considerable solvation of the active centre must be anticipated. As a result the charge density of the free cation will be reduced, and hence the lower value of fep represents the reactivity of a solvated free ion rather than a naked one. Confirmation of the apparent free ion nature of these polymerizations is afforded by the data on the ion pair dissociation constant,, of the salts used for initiation, and, more importantly, the invariance, within experimental error, of ftp with the counter-ion used (SbCl or BF4). Overall effects of solvent polarity will be considered shortly in more detail. 

Constants obtained by SXLSQI using the data shown in Fig. 7 up to [NaClO lmax. Pitzer parameters [168] and Masson coefficients [2 19] for sodium perchlorate used by SXLSQI were adopted assuming that the low concentration of solvent in the aqueous phase (see Table 11) has negligible effect on the aqueous ionic-activity and ion-volume properties. Solvent solubility parameters used by the program were taken from ref. [153]. Dielectric constants of the water-saturated solvents for use in the Debye-Hlickel treatment used in SXLSQI were 10.57 (TBP [220]), 13.63 (MIBK [221]), 17.5 (MIBC, estimated), and 37.4 (MeN02 [177]) the values for MIBC and MeN02 represent estimates based on an assumption of linear dependence of e on the volume fraction of water in the solvent. 

Figure 6.3. The degree to which organic solvents inhibit enzymes is dependent on their log P value. P is the partition coefficient of the solvent measured between octanol and water (i.e. P = solubility in octanol/solubility in water). Each point on the graph represents the activity of the enzyme in an reaction mixture containing water saturated with a solvent having the log P value shown. The reaction in this example is the microbial epoxidation of propene and butene. (From Laane et al., 1987, p. 73 reproduced by kind permission of Elsevier Science Publishers BV.)...

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