Effects Thermodynamic

Thermodynamic Effects 4.16.2.4.1 Intermolecular forces (i) Melting points and boiling points... 

Many more correlations are available for diffusion coefficients in the liquid phase than for the gas phase. Most, however, are restiicied to binary diffusion at infinite dilution D°s of lo self-diffusivity D -. This reflects the much greater complexity of liquids on a molecular level. For example, gas-phase diffusion exhibits neghgible composition effects and deviations from thermodynamic ideahty. Conversely, liquid-phase diffusion almost always involves volumetiic and thermodynamic effects due to composition variations. For concentrations greater than a few mole percent of A and B, corrections are needed to obtain the true diffusivity. Furthermore, there are many conditions that do not fit any of the correlations presented here. Thus, careful consideration is needed to produce a reasonable estimate. Again, if diffusivity data are available at the conditions of interest, then they are strongly preferred over the predictions of any correlations. 

Thermodynamic Effects of Shock Compression and the Hugoniot Curve... 

C Lee. Testing homology modeling on mutant proteins Pi edictmg stiaictural and thermodynamic effects m the Ala98 Val mutants of T4 lysozyme. Folding Des 1 1-12, 1995. 

The work on iron-nickel alloys has described shock-compression measurements of the compressibility of fee 28.5-at. % Ni Fe that show a well defined, pressure-induced, second-order ferromagnetic to paramagnetic transition. From these measurements, a complete description is obtained of the thermodynamic variables that change at the transition. The results provide a more complete description of the thermodynamic effects of the change in the magnetic interactions with pressure than has been previously available. The work demonstrates how shock compression can be used as an explicit, quantitative tool for the study of pressure sensitive magnetic interactions. 

In order to distinguish between kinetic and thermodynamic phenomena it is convenient to refer to the former as the 7tr/ i-effect and the latter as the tra/u-influence or static /ra/u-effect". though this nomenclature is by no means universally accepted. However, it appears that to account satisfactorily for the kinetic /rau.s-effect , both it (kinetic) and a (thermodynamic) effects must be invoked to greater or les.ser extents. Thus, for ligands which are low in the Trans series (e.g. halides), the order can be explained on the basis of a u effect whereas for ligands which arc high in the series the order is best interpreted on the basis of a jt effect. Even so, the relatively high position of H , which can have no rr-acceptor properties, seems to be a result of a a mechanism or some other interaction. 

The addition of metal hydrides to C—C or C—O multiple bonds is a fundamental step in the transition metal catalyzed reactions of many substrates. Both kinetic and thermodynamic effects are important in the success of these reactions, and the rhodium porphyrin chemistry has been important in understanding the thermochemical aspects of these processes, particularly in terms of bond energies. For example, for first-row elements. M—C bond energies arc typically in the range of 2, i-. i() kcal mol. M—H bond energies are usually 25-30 kcal mol. stronger, and as a result, addition of M—CH bonds to CO or simple hydrocarbons is thermodynamically unfavorable. 

Based on cathodic polarization curves, Dexter and Gao concluded that the increase of E for 316 stainless steel exposed to natural seawater was due to an increased rate of the cathodic reduction of oxygen at a given potential. It is not possible from Ecorr or polarization curves to decide whetlier the increase in Ecorr is due to thermodynamic effects, kinetic... 

Liu Z, EA Betterton, RG Arnold (2000) Electrolytic reduction of low molecular weight chlorinated aliphatic compounds structural and thermodynamic effects on process kinetics. Environ Sci Technol 34 804-811. 

There is a large amount of data available concerning the thermodynamic effects of ligands on other coordination sites (i. e., the thermodynamic cis- and iraws-effects). However, very little is known about the effects of ligands on the kinetic lability of other coordination sites. In fact, very little work has been carried out, directly with Bi2-derivatives, or with models of B12, on the kinetics of ligand substitution at the cobalt center. Of particular biochemical interest would be studies on the rate of displacement of coordinated benzimidazole by various ligands. Such work has not been reported at present. If the benzimidazole is replaced during enzymatic catalysis so that the lower axial position is occupied by some other Lewis base, one would expect this displacement, and the reverse step, to be very facile. This appears to be qualitatively true in that when water displaces benzimidazole as the benzimidazole is pro-... 

The thermodynamic effects of electric fields and are well known. Application of an electric field to a solution can affect the chemical equilibrium. For example, in Eq. (18) where C has a large dipole moment and B has a small dipole moment the equilibrium is shifted toward C under the action of an electric field. 

Hence, if thermodynamic effects of electric effect occur, the electric field strengths necessary are too high compared with ordinary operating conditions of microwave heating. 

It is therefore assumed that the p-variation in hydration comes only from a thermodynamic effect, related to a Y-dependent change in the stability of the intermediate, whereas in bromination, a transition-state shift adds to this latter effect, as expressed by (49) and (52), where log kY expresses the reactivity of PhCY=CH2. The second term in (52) is probably negligible in hydration... 

Our model predicts restabilisation at very high polymer concentrations. It is shown that this restabilisation is a thermodynamic effect, resulting from a decreased interparticle attraction, and is not kinetically determined, as proposed by Feigin and Napper. 

The process of crystallization is governed by kinetic and thermodynamic effects. The consideration of both of these is important in controlling the polymorphic form of a product. The available states (polymorphs) that a system may reach are defined by thermodynamics, but it is kinetics that guides the path taken between these states, and control when a given state will be reached in a process. In the time constrained environment of a production plant it is often... 

The size and complexity of the N-reactor plant and the limited amount of computing equipment that was available necessitated a judicious use of simplifying assumptions. For instance, primary coolant temperature transport lags were lumped into two groups, one each for the hot and cold loop legs thermodynamic effects in the secondary system condensate headers and surge... 

This allows us to define a thermodynamically effective equivalent radius Rf by replacing the actual sphere radius of a hard sphere by R j< which gives... 

On comparing results obtained in various solvents, it is practically only thermodynamic effects which can be explained and taken into account, whereas specific solvent effects which depend on the structure of the solvent molecule can only be dealt with empirically. Furthermore the dielectric constant changes with the solvent, and this affects the existence of ion pairs. This effect will always be troublesome for complexes in which a positively charged donor molecule is stabilized by a counter-ion. 

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. 

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