Arrhenius plot hydrolysis rate constants

Thus curvature in an Arrhenius plot is sometimes ascribed to a nonzero value of ACp, the heat capacity of activation. As can be imagined, the experimental problem is very difficult, requiring rate constant measurements of high accuracy and precision. Figure 6-2 shows a curved Arrhenius plot for the neutral hydrolysis of methyl trifluoroacetate in aqueous dimethysulfoxide. The rate constants were measured by conductometry, their relative standard deviations being 0.014 to 0.076%. The value of ACp was estimated to be about — 200 J mol K, with an uncertainty of less than 10 J moE K. ... 

In the above media the hydrolysis of bacterial cell walls has been studied between -1-20° and — 30°C. The rate constants lie on a straight line in the Arrhenius plot [logio k = /(1/T)]. Activation energies are 16.9 kcal mol in 40% methanol, and 20 kcal mol" in 50% MPD. The velocity in salty solutions is much more sensitive to salt action (inhibition) than to temperature. In the presence of 7 M NH4NO3, the rate factor it/ H20 9 X 10", and the calculated activation energy is =5.3 kcal mol". ... 

The isomerizations of n-butenes and n-pentenes over a purified Na-Y-zeolite are first-order reactions in conversion as well as time. Arrhenius plots for the absolute values of the rate constants are linear (Figure 2). Similar plots for the ratio of rate constants (Figure 1), however, are linear at low temperatures but in all cases except one became curved at higher temperatures. This problem has been investigated before (4), and it was concluded that there were no diffusion limitations involved. The curvature could be the result of redistribution of the Ca2+ ions between the Si and Sn positions, or it could be caused by an increase in the number of de-cationated sites by hydrolysis (6). In any case the process appears to be reversible, and it is affected by the nature of the olefin involved. In view of this, the following discussion concerning the mechanism is limited to the low temperature region where the behavior is completely consistent with the Arrhenius law. 

Taking the logarithm of bromide concentration in the water extracts (normalized to the weight of resin) for the Arrhenius plots in Figure 1 was based on the following assumption the level of Br ions accumulated over the period of extraction was proportional to the rate of RBr hydrolysis. This assumption would hold if the rate of hydrolysis (and hence ion release), Rh, were constant over that period of extraction. Under that assumption the following equation would apply ... 

Arrhenius plot for the myosin-catalyzed hydrolysis of adenosine triphosphate (ATP). Under the conditions of the experiments the rate tr is proportional to a rate constant k we may therefore plot loQio instead of iopiQ k, against 1 /T. 

The Arrhenius type plots were made to study the effect of temperature on rate constant (kj(). The activation energies were found to be 12.S4 kcal/gmoland 16.35 kcal/ gmol for the hydrolysis and oxidation reactions, respectively. These values also suggest that there was no influence of mass transfer and the reactions occur at the capsule surface. 

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