Theoretical interpretation temperature differences

One of the most important parameters is the temperature, the starting temperature, and the initial reaction rate. One can determine experimentally the initial reaction rate after elimination of diffusion and mass transport effects and then determine the Arrhenius constants, which depend on the temperature. The collision factor (ko) and activation energy (E) parameters influence significantly the activity pattern and selectivity. Figure 3.1 illustrates the influence of the temperature on these parameters for different reactions and metallic catalysts. This effect is known as compensation effect, although empirically there are attempts on theoretical interpretations for different heterogeneous systems [1, 2]. 

The temperature dependence of the Payne effect has been studied by Payne and other authors [28, 32, 47]. With increasing temperature an Arrhe-nius-like drop of the moduli is found if the deformation amplitude is kept constant. Beside this effect, the impact of filler surface characteristics in the non-linear dynamic properties of filler reinforced rubbers has been discussed in a review of Wang [47], where basic theoretical interpretations and modeling is presented. The Payne effect has also been investigated in composites containing polymeric model fillers, like microgels of different particle size and surface chemistry, which could provide some more insight into the fundamental mechanisms of rubber reinforcement by colloidal fillers [48, 49]. 

Although the rate of the reaction is the parameter in kinetic studies which provides the link between the experimental investigation and the theoretical interpretation, it is seldom measured directly. In the usual closed or static experimental system, the standard procedure is to follow the change with time of the concentrations of reactants and products in two distinct series of experiments. In the first series, the initial concentrations of the reactants and products are varied with the other reaction variables held constant, the object being to discover the exact relationship between rate and concentration. In the second series, the experiments are repeated at different values of the other reaction variables so that the dependence of the various rate coefficients on temperature, pressure, ionic strength etc., can be found. It is with the methods of examining concentration—time data obtained in closed systems in order to deduce these relationships that we shall be concerned in this chapter. However, before embarking on a description of these... 

The attempt to classify biological activities upon the basis of their velocities as affected by temperature involves for a number of cases the adjustment of curves to data inevitably subject to several sources of variation. One of these arises from the fact that the measurements may be secured with different individuals at each of several temperatures. The latitude of variation in series of data obtained in this way may be large, and unless great numbers of observations are available interpretation may be difficult. Indication already obtained as to the theoretical significance of the exact quantitative relationship between velocity of a vital process and temperatme make it desirable to demonstrate the limits of variation in material which is as nearly as possible biologically homogeneous. 

Rees and Thode (1966) reduced Se(VI) to Se(IV) with room temperature 8M HCl, and obtained a fractionation factor (ese(vi)-se(iv)) of 12%o ( 1). Interpretation of the results was complicated somewhat by the fact that the Se(IV) product was recovered by reduction to Se(0). The authors reported that some back-reaction of this precipitate may have occurred. They also presented some theoretical estimates of a, based on the theory of Bigeleisen (1949) and some assumptions about the nature of the reaction, that were consistent with the experimental results. In more recent experiments (Johnson et al. 1999), Se(VI) reduction by 4N HCl at 70°C yielded an ese(vi)-se(iv) value 5.5%o ( 0.3). The difference between this result... 

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