Thermodynamic explanation

The distribution coefficient is an equilibrium constant and, therefore, is subject to the usual thermodynamic treatment of equilibrium systems. By expressing the distribution coefficient in terms of the standard free energy of solute exchange between the phases, the nature of the distribution can be understood and the influence of temperature on the coefficient revealed. However, the distribution of a solute between two phases can also be considered at the molecular level. It is clear that if a solute is distributed more extensively in one phase than the other, then the interactive forces that occur between the solute molecules and the molecules of that phase will be greater than the complementary forces between the solute molecules and those of the other phase. Thus, distribution can be considered to be as a result of differential molecular forces and the magnitude and nature of those intermolecular forces will determine the magnitude of the respective distribution coefficients. Both these explanations of solute distribution will be considered in this chapter, but the classical thermodynamic explanation of distribution will be treated first. 

The region of immunity [Fig. 1.15 (bottom)] illustrates how corrosion may be controlled by lowering the potential of the metal, and this zone provides the thermodynamic explanation of the important practical method of cathodic protection (Section 11.1). In the case of iron in near-neutral solutions the potential E = —0-62 V for immunity corresponds approximately with the practical criterion adopted for cathodically protecting the metal in most environments, i.e. —0-52 to —0-62V (vs. S.H.E.). It should be observed, however, that the diagram provides no information on the rate of charge transfer (the current) required to depress the potential into the region of immunity, which is the same (< —0-62 V) at all values of pH below 9-8. Consideration of curve//for the Hj/HjO equilibrium shows that as the pH... 

The qualitative thermodynamic explanation of the shielding effect produced by the bound neutral water-soluble polymers was summarized by Andrade et al. [2] who studied the interaction of blood with polyethylene oxide (PEO) attached to the surfaces of solids. According to their concept, one possible component of the passivity may be the low interfacial free energy (ysl) of water-soluble polymers and their gels. As estimated by Matsunaga and Ikada [3], it is 3.7 and 3.1 mJ/m2 for cellulose and polyvinylalcohol whereas 52.6 and 41.9 mJ/m2 for polyethylene and Nylon 11, respectively. Ikada et al. [4] also found that adsorption of serum albumin increases dramatically with the increase of interfacial free energy of the polymer contacting the protein solution. 

The fact that mbber shows mbber elasticity was discovered more than 100 years earlier than professor H. Staudinger s proposal. The memory effect acquired by vulcanization, so-called Gough-Joule effect, and its thermodynamic explanation were the great achievements in the nineteenth century. As seen in many textbooks, this thermodynamic approach was the easiest one to gain consistency between ever-performed experiments and theory. In fact, thermodynamics of mbbery material can be treated in parallel with thermodynamics of gas. One could show experimentally that... 

Cahen D, Mirovsky Y (1985) Ternary Chalcogenide-Based Photoelectrochemical cells. 6. Is There a Thermodynamic Explanation for the Output Stability of CulnS2 and CulnSe2 Photoanodes J Phys Chem 89 2818-2827... 

Throughout most of this chapter we have been concerned with adsorption at mobile surfaces. In these systems the surface excess may be determined directly from the experimentally accessible surface tension. At solid surfaces this experimental advantage is missing. All we can obtain from the Gibbs equation in reference to adsorption at solid surfaces is a thermodynamic explanation for the driving force underlying adsorption. Whatever information we require about the surface excess must be obtained from other sources. 

The explanation of Ql(l effects just presented is rather typical of treatments found in most textbooks, in which a relatively simplified thermodynamic explanation, based on energy distribution patterns, is developed to account for effects of temperature on reaction rates. Such treatments of temperature effects, while correct overall, are abstract and nonmecha-nistic—a necessary property of thermodynamic explanations—and will be seen to be incomplete in important ways. In particular, thermodynamic treatments that eschew discussions of underlying mechanisms are unable to provide an explicit account of what steps in an enzyme-catalyzed reaction are rate limiting and, thus, responsible for Qio effects. 

Applicability of the first approach suggested by Keiko and Zarod-nyuk is based on the unity of thermodynamics and kinetics which explain differently the same physical regularities. As was said above this unity was brilliantly revealed by Boltzmann in his "kinetic" and "thermodynamic" explanations of the second law. In our case, setting, for example, a constraint on the equilibrium constant value of an individual reaction S VjXj = 0 within complex chemical process and writing this constraint intone of the possible forms ... 

The author proposes the following (thermodynamic) explanation of the phenomena of random fractal structure formation in porous materials. 

Fischer, E. W. Thermodynamical explanation of large periods in high polymer crystals and drawn fibers. Ann. N. Y. Acad. Sci. 89, 620—634 (1961). 

It should be pointed out, however, that the thermodynamic explanation of the chelate effect, in particular the contribution of entropy as presented above, is actually not as straightforward as it might appear. The entropy change for a reaction depends on the standard state chosen for reference and for very concentrated solutions one might chose unit mole fraction instead of one molal and the chelate effect would disappear. However, this is not realistic and for solutions one molal (or less) there is a real chelate effect. In very dilute solutions (0.1 M or less) where complexation of metal ions is generally most important, the chelate effect is of major importance and is properly understood as entropically driven. 

S. La Monica, P. Jaguiro, and A. Ferrari, A thermodynamical explanation for pore growing stability in porous silicon, Electrochem. Soc. Proc. 9tJ T), 140, 1997. 

The Direction of Change in Chemical Reactions Thermodynamic Explanation... 

The phase diagrams reflect the mutual oil-water solubilization properties of the nonionic surfactants, which can be understood, and then also predicted, only if the structures of the microemulsions (or the micellar aggregates) are known with some degree of certainty. Moreover the thermodynamical explanation of these properties in terms of the hydrophile-hydrophobe forces has to be founded on clear structural evidence and this is far from being the case at the present time (6). 

On the contrary, this set of experimental results would provide some ground for a theoretical and thermodynamical explanation of the evolution swollen micelle-microemulsion. Indeed each type of structure seems to reflect a domination of one or other component of the free energy of these nonionics at room temperature. Although a calculation and a discussion of these energy effects are well beyond the scope of the present paper, we can point out the importance of the forces specific to the hydrocarbon chain and to the oil beside the pure hydration forces. Van der Waals forces would favour the formation of a water layer, while entropic effects seem very important as far as the transitions hank-lamella and lamella-globule are concerned. These effects due to the solvent concentration (but also to the nature of the oil (2,5) are quite evident from the fine evolution of the phase diagrams, especially for water/surfactant ratios in the range 0.5-1.2. 

In particular, the relativdy large temperature coefficient of the electromotive force has found a complete thermodynamical explanation it is the conversion of 7 mols of... 

There are three basic concepts that explain membrane phenomena the Nemst-Planck flux equation, the theory of absolute reaction rate processes, and the principle of irreversible thermodynamics. Explanations based on the theory of absolute reaction rate processes provide similar equations to those of the Nemst-Planck flux equation. The Nemst-Planck flux equation is based on the hypothesis that cations and anions independently migrate in the solution and membrane matrix. However, interaction among different ions and solvent is considered in irreversible thermodynamics. Consequently, an explanation of membrane phenomena based on irreversible thermodynamics is thought to be more reasonable. Nonequilibrium thermodynamics in membrane systems is covered in excellent books1 and reviews,2 to which the reader is referred. The present book aims to explain not theory but practical aspects, such as preparation, modification and application, of ion exchange membranes. In this chapter, a theoretical explanation of only the basic properties of ion exchange membranes is given.3,4... 

A thermodynamic explanation of GC retention vs. temperature is based on the Van t Hoff equation, extended for GC ... 

Although this is a satisfactory picture to describe properties (1) and (3), it is possible to derive a more rigorous thermodynamic explanation, which follows. 

Normally, the assumption that inner and outer surfaces of the glass membrane have the same composition does not hold true, especially because the inner buffer solution is kept inside the electrode right from the production of the eleetrode and always stays there, whereas the outer surface is influenced by different solutions over the time of use. This gives rise to the so-called asymmetry potential. Further, one will usually find a sub-Nernstian slope, which is less than 0.059 V (at 25°C). (For the thermodynamic explanation, see [19]). Therefore an empirical equation of the following kind has to be used ... 

The experimental evidence for phase separation in polymer mixtures was briefly developed in the previous section. In the present section a thermodynamic explanation for mutual insolubility, or incompatibility, of polymer pairs will be outlined. 

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