Solvent thermodynamics

Whether AH for a projected reaction is based on bond-energy data, tabulated thermochemical data, or MO computations, there remain some fundamental problems which prevent reaching a final conclusion about a reaction s feasibility. In the first place, most reactions of interest occur in solution, and the enthalpy, entropy, and fiee energy associated with any reaction depend strongly on the solvent medium. There is only a limited amount of tabulated thermochemical data that are directly suitable for treatment of reactions in organic solvents. Thermodynamic data usually pertain to the pure compound. MO calculations usually refer to the isolated (gas phase) molecule. Estimates of solvation effects must be made in order to apply either experimental or computational data to reactions occurring in solution. 

This equilibrium is characterized by the ion product of the solvent— thermodynamic... 

Therefore, a complete description of the redox properties of sulfur and polysulfides in classical organic solvents has been obtained on the following basis only 8g and the radical anions 8 are reducible and only the dianions 8 and 8g are oxidable. The electrochemical process has been validated in DMF by comparing simulations and the experimental data in a wide range of temperatures (233 to 313 K) and scan rates (0.005 to 2.0 Vs ). It can be reasonably extended to other organic solvents. Thermodynamic and kinetic parameters have been discussed in Ref. 60. It must be noted that Paris et al. [58] describe the reduction of sulfur... 

Clark and Odell have found (39) that the susceptibility varies with temperature in a way that can be explained very well on the basis of temperature-dependent equilibria between diamagnetic and paramagnetic forms. This is valid equally for pyridine and for inert solvents. Thermodynamic quantities calculated from these measurements show that the paramagnetic forms have the lower enthalpies, and that there are relatively large increases of entropy on going from the paramagnetic to the diamagnetic forms. 

Surfactants are compounds that exhibit surface activity, or more generally, interfacial activity, and migrate to the interface when placed in solution. This migration results in lowering the solution surface tension (interfacial tension) as compared to the surface tension of the pure solvent. Thermodynamically, adsorption of a surfactant is deLned by the Gibbs adsorption equation ... 

Keywords Solution properties Conformational analysis Theta condition Excluded volume Good and poor solvent Thermodynamic theories Preferential adsorption Cosolvent effect... 

Y. Ishikawa, H. Kuwahara, T. Kunitake, Self-Assembly of BUayers from Double-Chain Fluorocarbon Amphiphiles in Aprotic Organic Solvents Thermodynamic Origin and Generalization of the Bilayer Assembly , J. Am. Chem. Soc., 116,5579 (1994)... 

Early studies of acids and bases were restricted to aqueous solutions and were made with an inadequate understanding of the peculiarities of water. The compounds were defined as substances which dissociated in water, the acids to give free hydrogen ions and the bases free hydroxide ions (Arrhenius, Ostwald, 1887). This definition does not express present views about aqueous solutions and cannot be applied to solutions in other solvents. Thermodynamics shows that free H+ ions cannot exist in appreciable concentration in water itself, and spectroscopy that the hydration of the proton is a strongly exothermic reaction. Accordingly the dissociation of an acid in water leads to often represented by H3O+ and referred to as the... 

Keywords Drug solubility Mixed solvent Thermodynamic consistency test... 

The number of moles of dissolved substance is n, and N denotes the number of moles of solvent. Thermodynamically speaking, it is most proper to express concentrations in terms of mole fraction. Actually, however, this method is used but little in studies of equilibria in solution. 

The solubility parameter is a very important property in science and has found widespread use in many fields and not just in the smdy of polymer-solvent thermodynamics. It is connected to the Flory-Huggins model as well, as explained in Section 16.3.3.2, but can also be used independent of it, as discussed in Sections 16.3.3.1 and 16.3.3.3. Several handbooks and reference books provide extensive lists of solubility parameters of numerous chemicals.The solubility parameter is defined as... 

The parameter x provides a measure of thermodynamic affinity of a solvent for the polymer, or a measure of the quality of the solvent. The smaller the x> the better is the solvent thermodynamically. For very poor solvents, x niay be higher than unity, and for very good ones, x be negative. Based on % values, solvents may be classified as ideal solvent (X = 2) ood solvent (x < ) and poor solvent (x > ). 

The maximum per cent hypochromism and the associated copolymer composition appear to be functions of the solvent used (see Table II) however, no simple correlation with solvent thermodynamic power was detected. To the contrary, a linear correlation with the solvent dielectric constant was demonstrated. In fact, the copolymer composition corresponding to the maximum hypochromism at 269.5 nm is lineally dependent on the solvent dielectric constant (see Figure 3). The intercept corresponding to the value dielectric constant = 1 (which means that there are no interactions of solvents) gives the copolymer composition really responsible for the maximum hypochromism, namely about 30 mole % methyl methacrylate. Furthermore, the maximum per cent hypochromism is a linear function of the solvent dielectric constant (see Figure 3) extrapolation gives a value of about 14%. 

In Fig. 2 the comparison of the dependences D (g), obtained according to the Eqs. (4) (points) and (25) (solid curves) is adduced. From this comparison a good correspondence of the dependences D g), obtained by both indicated modes and, as consequence, the possibility of the Eq. (25) application for D. calculation by the known values g or, vica versa, g values by the known magnitudes D. follows. The solvent type influence in the Eq. (25) is taken into account by intrinsic viscosities [q]g and [q]j logarithmic difference, adduced in brackets — the better solvent thermodynamical quality in respect to polymer, the larger this difference is and,... 

The authors [91] proposed description of organic phase influence on limiting characteristics of polyurethanearylates (PUAr) interfacial polycondensation. As it is known [55], one from the methods of polymer solubility parameter 5 experimental determination is plotting of the dependence of intrinsic viscosity [t ], measured in several solvents, on this solvents solubility parameter 5 value. The smaller difference 6p-5J or the better solvent thermodynamical quality in respect of polymer is, the larger [q] is. The dependences [q](5 ) have usually belllike shape and such dependence maximum corresponds to 5 [55]. In Fig. 23 the dependence of on 5 of solvents, used as organic phase at PUAr interfacial polycondensation is adduced. The dependence q /S ) bell-like shape is obtained again and its maximum corresponds to 5 10 (cal/cm ), that is a reasonable estimation for PUAr [36, 55]. Let us note that all q values were determined in one solvent, which was not used at synthesis, namely, in mixture phenol-simm-tetrachloroethane. The dependence qj 4(5 ), adduced in Fig. 23, allows to make two conclusions. Firstly, the value q, reached in PUAr interfacial polycondensation process, is controlled by solvent thermodynamical qnality and the greatest... 

Kozlov, G. V. Musaev, Yu. 1. Shustov, G. B. Burmistr, M. V. Korenyako, V. A. Kinetics of high-temperature poly condensation influence of synthesis temperature and solvent thermodynamical quality. Problems of Chemistry and Chemical Technology, 2001, (2), 106-109. 

Figure 1. Schematic diagram of categories involving polymer structure and solvent thermodynamics by which to study crystallization/gelation.

Certainly, the second virial coefficient A-i also determines the solvent thermodynamic quality, being related (in this approximation) to x, by Equation 52 and to other parameters by Equations 53 and 54, which is shown in Figure 3.4. 

The argument made above not withstanding, the pure solvent thermodynamics, including coexistence curve location, critical parameters, and dielectric constant are, in fact, rather well reproduced by the SPC models, and SPC/E in particular[54, 55]. Further, when the SPC/E model is applied to SCW, the calculated structural results agree with recent experimental neutron scattering data approximately as well in SCW as in ambient water[15, 16]. Hence, the SPC models have shown themselves to be remarkably robust caricatures of fluid water, and well supported for our studies of SCW. 

Solvent type does not seem to affect the efficiency of the fractionation process in any significant way. Different solvent types simply shift Tref profiles to higher or lower elution temperatures depending on the interactions between polymer and solvent. Thermodynamically good solvents shift Tref profiles to lower elution temperatures, while poorer solvents do the opposite. Calibration curves prepared using different solvents were reported to be almost parallel (Fig. 15) [31], which indicates that the choice of solvent in Tref is of minor importance. 

For polymer solutions, a decrease in the solvent thermodynamic quality tends to decrease the polymer-solvent interactions and to increase the relative effect of the polymer-polymer interactions. This results in intermolecular association and subsequent macrophase separation. The term colloidally stable particles refers to particles that do not aggregate at a significant rate in a thermodynamically unfavourable medium. It is usually employed to describe colloidal systems that do not phase separate on the macroscopic level during the time of an experiment. Typical polymeric colloidally stable particles range in size from 1 nm to 1 xm and adopt various shapes, such as fibres, thin films, spheres, porous solids, gels etc. 

The latent heat of evaporation is much higher for water, than for organic solvents. Thermodynamically driven evaporation of water occurs more slowly at room temperature. 

Tsvetkov, V.G., Kaimin , I F., loelovich, M.Ya., and Prokhorov, A.V., Enthalpy of interaction of cellulose and some of its model compoimds with solvents. Thermodynamics of organic compounds, Gorki GSUniv. Press., 1982, pp. 54-60 (in Russian). 

Marchenko, G.N., Tsvetkov, V.G., Marsheva, V.N., Tsvetkova, L.Ya., and Vasil ev, N.K., Thermochemical investigation of chitin interaction with some solvents. Thermodynamic properties of solutions, Ivanovo Khimiko-Tekhnologich. Institut Publ., 1984, pp. 37-39 (in Russian). 

JON Jones, A.T., Danner, R.P., and Duda, J.L., Influenee of high pressure gases on polymer-solvent thermodynamic and transport behavior, J. Appl. Polym. Sci., 110, 1632, 2008. 

The coordination number collective variable is a good choice for modeling solvent thermodynamics of ions in solution. The coordination number of species A with respect to species B is defined using a Fermi-Dirac function as... 

---