Frequency factor Arrhenius plots

A plot of In k against the reciprocal of the absolute temperature (an Arrhenius plot) will produce a straight line having a slope of —EJR. The frequency factor can be obtained from the vertical intercept. In A. The Arrhenius relationship has been demonstrated to be valid in a large number of cases (for example, colchicine-induced GTPase activity of tubulin or the binding of A-acetyl-phenylalanyl-tRNA to ribosomes ). In practice, the Arrhenius equation is only a good approximation of the temperature dependence of the rate constant, a point which will be addressed below. 

The main point of interest in Fig. 27 is that there appears to be a break in the Arrhenius plot. At low temperatures a reaction with a low frequency factor and an activation energy not far from zero seems to take place. At higher temperatures another reaction with a higher frequency factor and activation energy appears to predominate. 

Quantitative investigations of the photoinduced electron transfer from excited Ru(II) (bpy)3 to MV2 + were made in Ref. [54], in which the effect of temperature has been studied by steady state and pulse photolysis techniques. The parameters ve and ae were found in Ref. [54] by fitting the experimental data on kinetics of the excited Ru(II) (bpy)3 decay with the kinetic equation of the Eq. (8) type. It was found that ae did not depend on temperature and was equal to 4.2 + 0.2 A. The frequency factor vc decreased about four orders of magnitude with decreasing the temperature down to 77 K, but the Arrhenius plot for W was not linear, as is shown in Fig. 9. 

This expression has the Arrhenius form and E is the maximum value of the potential energy, an activation energy for deposition. This is expected because the potential profile of fig. 2 resembles the plot of the energy against reaction coordinate used in the theory of rate processes. The factor /(//m) accounts for the dependence of the diffusion coefficient on the distance and evaluations show that it can decrease the frequency factor in eqn (16) by two orders of magnitude. 

Within measurement precision ( 10%) the various peaks gave linear Arrhenius plots with activation energies between 15 and 40 kcal/ mole. Assuming an average 25 kcal/mole, a reasonable 5 kHz impact frequency at room temperature (25°C) would extrapolate to ca. 10°C at 11 Hz, one of the Rheovibron measuring frequencies. Therefore the magnitude of the dissipation factor subsequently used for the correlation was 10°C, 11 Hz. 

The isomerization of 8 -HOABA and 37 was observed as a first-order reaction in which the rate was proportional only to the concentration of the 8 -hydroxyl compound. As the pH and temperature increased the reaction proceeded more rapidly. At 25°C, the half-life of 8 -HOABA was 30 hr at pH 3, 4 hr at pH 7, and shorter than 1 min at pH 10, that is, 8 -HOABA was isomerized to PA more rapidly at pH 10 than at pH 3 by a fa.ctor of 2,000. The temperature dependence of the rate was greater under alkaline conditions than under acidic conditions. The Arrhenius plots of the rate constants gave the activation energies of Arrhenius and frequency factors, which were converted to the kinetic parameters, i.e. the activation enthalpy activation entropy (4S ) and activation free... 

An Arrhenius plot k indicated that the frequency factor. A, and the activation energy, E, were 4.5 x 10 h and 42.9 kj/mol, respectively. The calculated activation energy for the reaction between propylene and EBHP is slightly higher than... 

These two constants depend only on temperature. If data had been available at a series of temperatures, In k could have been plotted against 1/T to obtain the activation energy E and the frequency factor A, according to the Arrhenius equation. The adsorption equilibrium constant would also be expected to be an exponential function of temperature, according to a van t Hoff type of equation,... 

The kinetics of denaturation of peptide and protein drugs have not been extensively treated. Some studies on the temperature dependence of denaturation rates have been reported. A kinetic study of the denaturation of G actin in solution using DSC yielded linear Arrhenius plots, from which values for the activation energy and the frequency factor of 23 1 kJ/mol (55.2 kcal/mol) and 76.8 sA respectively, were obtained (Fig. 215).889 Linear... 

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