Activation energy exchange

Tensile relaxation modulus Tensile stress relaxation modulus Threshold energy of coagulation Activation energy Exchange energy of i-j contact Helmholtz free energy (F = E—TS)... 

Activated diffusion of the adsorbate is of interest in many cases. As the size of the diffusing molecule approaches that of the zeohte channels, the interaction energy becomes increasingly important. If the aperture is small relative to the molecular size, then the repulsive interaction is dominant and the diffusing species needs a specific activation energy to pass through the aperture. Similar shape-selective effects are shown in both catalysis and ion exchange, two important appHcations of these materials (21). 

In theory two carbanions, (189) and (190), can be formed by deprotonation of 3,5-dimethylisoxazole with a strong base. On the basis of MINDO/2 calculations for these two carbanions, the heat of formation of (189) is calculated to be about 33 kJ moF smaller than that of (190), and the carbanion (189) is thermodynamically more stable than the carbanion (190). The calculation is supported by the deuterium exchange reaction of 3,5-dimethylisoxazole with sodium methoxide in deuterated methanol. The rate of deuterium exchange of the 5-methyl protons is about 280 times faster than that of the 3-methyl protons (AAF = 13.0 kJ moF at room temperature) and its activation energy is about 121 kJ moF These results indicate that the methyl groups of 3,5-dimethylisoxazole are much less reactive than the methyl group of 2-methylpyridine and 2-methylquinoline, whose activation energies under the same reaction conditions were reported to be 105 and 88 kJ moF respectively (79H(12)1343). 

In view of the enthalpy and activation energy (see Section II, B, 1) of the decomposition of arylpentazoles the activation energy for the reversal of the decomposition, the 1,3-addition of elementary nitrogen to arylazides, can be estimated to be 25-30 kcal/mole, an amount which does not exclude the reaction. To ascertain whether the decomposition of arylpentazoles is a reversible reaction, p-ethoxyphenylazide-[j8-N ] (see Section II, B, 3) adsorbed on charcoal was exposed to unlabeled nitrogen (45-50°, 380 atm, 100 hr), but the anticipated exchange of between the reactants was not detected. ... 

J mol ). This is additional evidence in favor of rate limitation by inner diffusion. However, the same reaction in the presence of Dowex-50, which has a more open three-dimensional network, gave an activation energy of 44800 J mol , and closely similar values were obtained for the hydrolysis of ethyl acetate [29] and dimethyl seb-acate [30]. The activation energy for the hydrolysis of ethyl acetate on a macroreticular sulphonated cationic exchanger [93] is 3566 J mol . For the hydrolysis of ethyl formate in a binary system, the isocomposition activation energy (Ec) [28,92] tends to decrease as the solvent content increases, while for solutions of the same dielectric constant, the iso-dielectric activation energy (Ed) increases as the dielectric constant of the solvent increases (Table 6). 

We conclude with a consideration of a few other cobalt self-exchange reactions. The reaction in Eq. (9.33) is faster than that involving the ammine complexes (Eq. 9.30) because the water is a weaker-field ligand than ammonia. Thus, the activation energy for the formation of the electronically excited states is lower, as is the change in Co-ligand distances in the two oxidation states. 

The corresponding overall activation energy obtained was 33 kcal.mole . At 100 °C, the measured half-time for exchange was 13 min. 

Stranks has reported the activation energy and entropy for the exchange system Cr(urea)6 -Cr(urea)6, to be 13 kcal.mole and — 40 cal.deg . mole . ... 

Horne and Axelrod have suggested that this exchange may not be first order with respect to each iron oxidation state at high thiocyanate concentrations. A lower value for the rate coefficient kg and a slightly higher activation energy than that quoted previously have been reported ... 

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