Factors Affecting Equilibrium Constants

It is always important to keep in mind the relative nature of substituent effects. Thus, the effect of the chlorine atoms in the case of trichloroacetic acid is primarily to stabilize the dissociated anion. The acid is more highly dissociated than in the unsubstituted case because there is a more favorable energy difference between the parent acid and the anion. It is the energy differences, not the absolute energies, that determine the equilibrium constant for ionization. As we will discuss more fully in Chapter 4, there are other mechanisms by which substituents affect the energy of reactants and products. The detailed understanding of substituent effects will require that we separate polar effects fiom these other factors. 

J.P. Guthrie, Carbonyl addition reactions Factors affecting the hydrate-hemiacetal and hemiacetal-acetal equilibrium constants. Can. J. Chem. 53 (1975) 898-906. 

What is equilibrium constant Which factors affect the equilibrium constant ... 

IfK2, kl9 k u and k2 had the same values as K 2, k u k l9 and k 2, then the optical purity of the product, RH, would be determined solely by the value of the diastereomeric equilibrium constant Kv If, however, the primed and unprimed constants were different, the final optical yield could be determined by both thermodynamic and kinetic factors, and in one extreme could result in the observation that the preferred enantiomer of the product originated in the minor dia-stereomer. Clearly, kinetic factors can be important since the steric interactions of the initial two diastereomers are different and these could affect the rate constants of the reaction. Moreover, the o--alkyl intermediate is chiral, as shown for one of the initial olefin diastereomers in Figure 4, and the rate of hydrogen addition and insertion... 

With a given system of constant K, a decrease of E/R increases y, but decreases y. Therefore, an optimum operation condition has to be determined based on the various factors affecting the economy of the separation processes, such as the value of products, equipment costs, and operating costs. It is interesting to note that Y depends on the ratio E/R, but not on the values of E and R. Can we increase E and R indefinitely to maintain the same y as long as E/R is constant for a continuous extractor The answer is "no." We should remember that Eq. (10.13) is based on the assumption that the extractor is in equilibrium. Therefore, the increase of E and R will shorten the residence time as a result, the extractor cannot be operated in equilibrium and y will decrease. 

The thermodynamics and kinetics of the thermal equilibrium between previtamin D3 and vitamin D3 have been studied (34,35). The isomerization of previtamin D3 to vitamin 63 is an exothermic first order reaction. The vitamin D3/previtamin D3 equilibrium ratio depends on the temperature and can be calculated from the appropriate equilibrium and kinetic constants reported by Hanewald et al. (36). The rate constants for the equilibrium have been shown to be independent of the nature of the solvent, of acidic or basic catalysis and of factors known to affect free radical process (37,38). The percentages of vitamin D3 in equilibrium with previtamin D3 ranges from 98% at -20° to 78% at 80°. Thus, when vitamin D3 is stored in the cold, the equilibrium constant hinders the conversion to previtamin D3. 

The nature of the cation (K+ or Na+) in hydroxides has been found to affect the temperature plot of the equilibrium constants of the reaction of KOH and NaOH with 2,6-di-r-butylphenol (ArOH). The nature of the cation in the resulting phenoxides ArOK or ArONa is a factor determining the kinetics of the addition of ArOH to CH2=CHC02Me. Two different kinetic schemes have been proposed to describe the transformation of ArOH in the presence of ArONa or ArOK.137... 

Because chemical equilibrium involves rates of reactions, this chapter first investigates the factors that affect the rate of a reaction (Section 18.1). The molecular basis of chemical equilibrium and some of its terminology are then presented in Section 18.2. LeChatelier s principle, discussed in Section 18.3, explains qualitatively how to predict what happens to a system at equilibrium when a change is imposed on the system. Section 18.4 presents the equilibrium constant, which allows us to obtain quantitative results for systems at equilibrium. 

The equilibrium constant expression is in the same form as the ratio in the Nemst equation (Chapter 17). The square brackets mean the molarity of the substance they enclose, and the constant K is called the equilibrium constant. The entire equation is known as the equilibrium constant expression. No matter what the initial concentrations of reactants or products, the ratio of the concentrations at equilibrium will be equal to the constant K. The value of K depends only on the specific chemical equation and on the temperature. It does not depend on any of the other factors that can affect the rate of a reaction. For example, if different quantities of the same reactants and products are introduced into different reaction vessels, they will react with one another until, at equilibrium, the same ratio of concentrations, each raised to the appropriate power, is established. 

Significant differences in the equilibrium constants for carbon monoxide binding to cytochromes P450 from bacterial, liver microsomal, and adrenal cortex microsomal sources, different isozymes of the liver microsomal proteins, and for substrate-free and substrate-bound enzymes, have been observed and have been related to similar factors that affect O2 and CO binding in oxygen transport and storage heme proteins. The importance of the cis and tmns effects, that is electronic effects associated with the porphyrin... 

In these systems, the donor and acceptor diffuse together to give a precursor complex, D A, whose formation is described by the equilibrium constant Kp. Electron transfer, characterized by rate constant eTj occurs within the associated donor-acceptor pair, converting the precursor complex to successor complex D A. Subsequent separation of the oxidized donor (D+) and reduced acceptor (A ) from the successor complex is described by. s- The rate of m/ermolecular electron transfer depends not only on the factors that influence kpj but also on factors affecting the formation of the precursor complex [19]. More quantitatively, as described by Eq. 2, the expression for intermolecular electron transfer has the form of a consecutive reaction mechanism described by an observed rate constant (A obs) consisting of rate constants for diffusion (A ) and the activated electron transfer. 

With the goal of removing as much of the phytochemical of interest from the plant raw material as quickly as possible, knowledge of the concepts of equilibrium and mass transfer is essential for economically operating extraction equipment. Extraction variables and operation are chosen to maximize the value of the equilibrium constant, K, in Equation 11.1 and the rate of extraction, 8C/5t, in Equation 11.2. These two equations show that only four factors affect extraction operation ... 

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