Enthalpy self-exchange

The significance of these quantities is analogous to that for the activation parameters for homogeneous self-exchange reactions. Thus, AH equals the activation enthalpy for conditions... 

Intrinsic enthalpy of activation for homogeneous self-exchange. Values for v + + and... 

In Table 1 are summarized representative examples of self-exchange rate constant data for a variety of different types of redox couples based on metal complexes, organometallic compounds, organics and clusters. Where available the results of temperature dependence studies are also cited. For convenience, data obtained from temperature dependence studies are presented as enthalpies and entropies of activation as calculated from the reaction rate theory expression in equation (14). 

The rate constants (kex) of the electron exchange reactions between ZnTPP+ and ZnTPP [Eq. (1)] were determined using Eq. (2), where AHms( and AH°msi are the maximum slope linewidths of the ESR spectra in the presence and absence of ZnTPP+, respectively, and P, is a statistical factor [14]. From the linear plots of (AHmsi - Afi°msl) and [ZnTPP] at various temperatures are obtained the self-exchange electron-transfer rate constant (k ). The Arrhenius plots are shown in Fig. 13.3 together with the observed activation enthalpies (AHols ), where the effect of diffusion (kdiff) is taken into account. The AHol/ values are all positive and decrease in order toluene > MeCN > CH2C12 [16],... 

An additional contribution to equation 23), Rln gl/gs), arises from any difference in the spatial degeneracy of the ground and transition state for a self-exchange reaction this contributes aboutO.6 J M L Differences in the densities of vibrational states will also contribute in cross electron-transfer reactions. The activation enthalpy is... 

Self-assembly is a thermodynamically controlled process. The formation of the capsules and the exchange of guest molecules proceed within seconds to hours, sometimes days, but finally, an equilibrium is reached which is governed by a finely balanced interplay of enthalpy and entropy. A... 

ITC has been used to determine the equilibrium constant of supramolecular polymers formed either from complementary monomers [201] or from self-complementary monomers [92,164], In the former case, the A - A monomer solution is injected into the B - B monomer solution. The exchanged heat measured is proportional to the number of hydrogen bonds formed and thus directly related to the equilibrium constant, hi the latter case, the self-complementary monomer is simply diluted into pure solvent. This time, the exchanged heat measured is proportional to the munber of hydrogen bonds broken and related to the self-equilibrium constant. ITC is a very powerful technique because equilibrium constants as high as 10 Lmol are accessible [202]. Moreover, a single experiment yields the equihbrium constant together with the molar enthalpy of association (Affassoc)-... 

A large number of materials can be prepared via new metathetical (exchange) solid-state precursor reactions. This synthetic route is extremely rapid (often < 1 sec.), can be initiated at low temperature, and is potentially useful for controlling particle size and for preparing both cationic and anionic solid solutions. The often self-propagating and sometimes explosive behavior observed in these reactions is related to their exothermidty. Consequently, thermodynamic considerations can be employed to help select the best set of precursors as judged from reaction enthalpies. The control of particle size and product yield through manipulations of reaction temperature and the factors that influence reaction initiation in these systems are discussed. 

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