Partition temperature effect

Octano/—Water Partition Coefficient. The Fragment approach (234—236) has been reviewed (227) and another method similar to the UNIFAC refit for Henry s constant has been proposed. Improved accuracy for many species and the abiUty to correct for temperature effects have been claimed for the newer method. 

Liiers, F., ten Hulscher, Th.E.M. (1996) Temperature effect on the partitioning of polycyclic aromatic hydrocarbons between natural organic carbon and water. Chemosphere 33, 643-657. 

Carbonate rocks and foraminifera tests (a sample of mixed species) are consistently lower in 5 Mg than Mg from seawater by several per mil. In addition. Mg in calcite is consistently lower in 5 Mg than Mg in dolomite by approximately 2%o (Fig. 1). These data together with the samples of coeval speleothem calcite and waters show that the heavy isotopes of Mg partition to water relative to carbonate minerals. In this respect the Mg isotopes behave much like the isotopes of Ca (Gussone et al. 2003 Schmitt et al. 2003). There is not yet sufficient data to assess with confidence the temperature dependence of the fractionation of Mg isotopes between carbonates and waters, although Galy et al. (2002) concluded that the evidence so far is that temperature effects are below detection in the range 4-18°C. 

It is apparent from early observations [93] that there are at least two different effects exerted by temperature on chromatographic separations. One effect is the influence on the viscosity and on the diffusion coefficient of the solute raising the temperature reduces the viscosity of the mobile phase and also increases the diffusion coefficient of the solute in both the mobile and the stationary phase. This is largely a kinetic effect, which improves the mobile phase mass transfer, and thus the chromatographic efficiency (N). The other completely different temperature effect is the influence on the selectivity factor (a), which usually decreases, as the temperature is increased (thermodynamic effect). This occurs because the partition coefficients and therefore, the Gibbs free energy difference (AG°) of the transfer of the analyte between the stationary and the mobile phase vary with temperature. 

In Illustrative Example 20.3 it is shown how water temperature influences the air-water exchange velocity, v,Ww. An additional temperature effect of the air-water flux results from the temperature dependence of the air-water partition constant, A,Ww. If water and air temperatures are different, the question arises whether the equilibrium between the air and water phase is determined by water temperature, by air temperature, or even by a mixture of both. Explain why Ki3lv/ should be evaluated for the temperature of the water, not the air. 

Caution should be exercised when considering temperature effects on solubilization by micelles, since the aqueous solubility of the solute and thus its micelle/water partition coefLcient can also change in response to temperature changes. For example, it has been reported that although tt solubility of benzoic acid in a series of polyoxyethylene nonionic surfactants increases with temperature, the micelle/water partition coefLci rt, shows a minimum at 2C, presumably due to the increase in the aqueous solubility of benzoic acid (Humphreys and Rhodes, 1968). The increasr in Km with increasing temperature was attributed to an increase in micellar size, as the cloud point temperature of the surfactant is approached (Humphreys and Rhodes, 1968). 

The media used in aqueous chemistry have a huge influence on the reaction thermodynamics and must be taken into account. These effects were often ignored in a large number of papers in the past. The purpose of this paragraph is to remind the reader that the effects of media govern the reaction constants not only in pure aqueous solutions but also in partition experiments [28,29,30]. Temperature effects will not be treated here, but they are of significant importance [29]. 

Temperature Effect The effect of temperature on the value of the partition ratio can vary greatly from one system to another. This depends on how the activity coefficients of the components in each phase are affected by changes in temperature, including any effects due to changes in mutual solubility with temperature. For a given phase, the Gibbs-Helmholtz equation indicates that... 

During the last five or six years Siekierski and his coworkers (50—54) have investigated a large number of data involving the partition coefficients (separation factors), the influence of enthalpy and entropy on the separation factors, temperature effect on the extraction and have plotted these quantities and others, like the unit cell volumes, radii etc. for the lanthanides and a few of the actinides to enumerate their double-double (tetrad) hypothesis. In many of these plots they have used the... 

Han et al. [39] further found that the diffusion coefficient of the mononuclear HC red 3 increased with pH, with dye concentration (1.0 to S.Og/liter), and with increasing temperature (25 to 60°C). However, changing the dyebath solvent from water to 50vol % aqueous ethanol decreased dye uptake, but the diffusion coefficients remained similar in magnitude. The pH effect can be explained by increased swelhng of the hair, and the dye concentration and temperature effects are consistent with expectation for a diffusion-controlled interaction. The solvent effect occurs because the dye is more soluble in the ethanol-water system than in water alone, thereby increasing the affinity of dye for the solvent phase relative to the keratin and causing more of the dye to partition into the aqueous-ethanol phase and less into the hair. 

The dielectric continuum models may allow us to predict speciation in aqueous solutions as a function of temperature simply by changing dielectric constant of the polarizing medium. At first glance, this may simply appear to be a return to the Bom-model formalism. However, the inner sphere solvation would be included explicitly. To include temperature effects on the inner solvation shells, we would have to calculate the partition functions of the cluster defining the metal atom and its first and, possibly, second coordination environment. 

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