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Kinetic and thermodynamic measurements

When a component A is added to a solvent, there is a volume change usually the volume increases but occasionally it decreases. The volume change on adding 1 mol of A is termed the partial molar volume, and it is denoted by It is dependent on all the thermodynamic conditions the temperature, the pressure, the nature of the solvent, the concentration of A, the concentration of all the other solutes, and any other pertinent thermodynamic variables. Measuring is equivalent to measuring the solution density at specified conditions, a measurement that can be made quite accurately. For stable solutes, partial molar volumes are frequently quoted to a precision of 0.01 cm mol It often suffices to consider only the partial molar volume at [Pg.267]

Le Chatelier s principle assures us that if external pressure is applied to a solution, the chemical equilibrium, characterized by the equilibrium constant K, will change in the direction that reduces the solution volume, which depends on AK , so that [Pg.268]

It is apparent that AU can be determined either by measuring the partial molar volumes of the products and reactants and subtracting the volume of the reactants from that of the products or by measuring the pressure dependence of K. There is also a third method this involves the pressure dependence of the rates for the forward and backward reactions, as discussed below. [Pg.268]

By analogy with the thermodynamic treatment of the solute equilibrium, transition-state theory describes rates of chemical change by postulating that a transition state lies somewhere on the pathway between the reactants and the products and that this transition state can be characterized by its own thermodynamic parameters, including its partial molar volume. The difference between the partial molar volume of the transition state and that of the reactants is the activation volume, AU. The activation volume cannot be measured by a direct density measurement, because the transition state is not a chemical species, not even a short-lived one. It can be measured only by the effect of the pressure on some rate constant k that characterizes the chemical process  [Pg.268]

The complete characterization of a reaction requires that the temperature dependence of the equilibrium constant and all the pertinent rates are also measured, so that the enthalpies, entropies, and free energies for the reaction and for the transition state are also known. Such temperature effects are familiar to most chemists, since they are accustomed to thinking about [Pg.268]


Clearly, it takes an extensive series of kinetic and thermodynamic measurements to characterize a system of this complexity. [Pg.148]

In the literature there are no quantitative studies on the kinetics and thermodynamics of stoichiometric superoxide reactions with metal centers in general, and metalloporphyrins in particular. More precisely, superoxide concentration and temperature dependent kinetic and thermodynamic measurements were never reported and consequently the rate constants, activation parameters or binding constants for this t5rpe of reactions (Scheme 15) are not known. (The catalytic rate constants for the superoxide disproportionation, i.e., dismutation, by metal complexes are known (see earlier), however in those measurements the concentration of a catalytic amount... [Pg.88]

Kinetic and thermodynamic measurements show that 2-phenylacetylthiophene (92a) has a low enol content K = 3.55 x 10 7 (or )K = 6.45).136 The keto and enol tautomers have pKa values of 14.60 and 8.15, respectively. Relative to a phenyl or furanyl substituent at the carbonyl carbon, the thiophene increases the acidity of the enol tautomer, but stabilizes the ketone, probably via the resonance contribution (92b). Thus 2-thiophenyl stabilizes the enolate by electron attraction, but the ketone by donation. Effects of micelles on the equilibria are also reported. [Pg.24]

Theoretical calculations share with gas-phase kinetic and thermodynamic measurements the common aim of the understanding of the intrinsic reactivity properties of heteroaromatic compounds. The purpose of this subsection is to consider the predictive value of theoretical methods insofar as ionic substitution reactions on simple heteroaromatics are concerned. The topic under discussion is inherently limited by the wide range of interest in the understanding of the principles of these processes in solution. It is exactly in this field that an appropriate amount of data concerning gas-phase structural and reactivity properties of heteroaromatic compounds is at present available from modern experimental techniques that can be tested against theoretical predictions. [Pg.27]

In order to get an insight on the plausible mechanism for the reaction and learn about the influence of aldehyde, catalyst, and temperature on the reaction rate, kinetic and thermodynamic measurements were performed. Kinetic studies of the Cp2 ThMe2-catalyzed Tishchenko reaction of benzaldehyde indicates that the reaction follows a first order dependence on both catalyst and aldehyde (23) [115]. [Pg.179]

In this system, all of the compounds that have been detected in or isolated from solutions of catalytic reactions lie off of the major catalytic pathway. These species are shown outside of the dotted enclosure in Scheme 15.6. The substances within the dotted enclosure are the proposed catalytic intermediates. The accumulation of the complexes outside the dotted enclosure in Scheme 15.6 reduces the rate of the catalytic reaction. This phenomenon should not be assumed to be the case for all catalytic systems species lying directly on the catalytic cycle Imve been observed directly in many other systems. However, ttiis study did show that the identification pf a detectable species in a catalytic system without kinetic data to assess the connection between the observed species and the catalytic cycle can lead to incorrect interpretations of the reaction mechanism. As stated by the authors of the previous version of this text, "Only when kinetic and thermodynamic measurements define the role of complexes along the actual reaction path can the mechanism be defined."... [Pg.589]

Furthermore, in formulating the transformations of starting materials to products, it is often the case that evidence has accumulated that the pathways by which the former are converted to the latter involves the intermediacy of carbocations, carb-anions, and free radicals and kinetic and thermodynamic measurements have been made. [Pg.1022]


See other pages where Kinetic and thermodynamic measurements is mentioned: [Pg.206]    [Pg.75]    [Pg.200]    [Pg.183]    [Pg.27]    [Pg.262]    [Pg.161]    [Pg.267]    [Pg.269]    [Pg.271]    [Pg.273]    [Pg.275]    [Pg.277]    [Pg.279]    [Pg.281]    [Pg.283]    [Pg.285]    [Pg.287]    [Pg.289]    [Pg.291]    [Pg.293]    [Pg.295]    [Pg.297]    [Pg.299]    [Pg.301]    [Pg.303]    [Pg.305]    [Pg.261]    [Pg.1126]    [Pg.706]   


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