Effect of the Activation Energy

Let us recall that the activation energy is determined by plotting the rate constant expressed in logarithm form, Lnkj, versus the reciprocal temperature, y, this tan-perature being expressed in kelvin. An error can be made on the value obtained for the slope of this curve, which is equal toy and thus another error is made for the value of the exponential factor k, which compensate for the previous error, so as to keep the same value of kj. 

The effect of the value of the activation energy on the process is evaluated by taking the value of Inkj = -5.94 obtained at 180°C and the couples of the associate values calculated from the relationship kj = k - exp[-- ]  

the temperature-time history and the state of cure-time history are calculated either at the mid-plane or on the surface of a rubber sheet of thickness (2L) 2 cm, during the cure at 170°C, by taking the three couples of values shown above. 

The effect of the activation energy on the cure of the rubber sheets can be appreciated in the following figures  

The following conclusions can be drawn from these curves  

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Baer and Ryan (Bl) have extended the calculations of Hicks and Frazer by analyzing the effect of the activation energy on the time required to achieve runaway reaction conditions. Their calculations demonstrated that the slope on a plot of log(r)1/2 versus log Q is related to the activation energy of the propellant-heating reaction by the expression... 

Figure 8. Tubular plug-flow addition polymer reactor effect of the activation energy (E) of the initiator on the molecular weight-conversion relationship at constant frequency factor (k ). Each point along the curves represents an optimum initiator feed concentration-reactor jacket temperature combination and their values are all different. (In k = 26.494 In sec 0.0 mol % solvent)...

In Figs. 8a and 8b the effect of the activation energy and the membrane thickness on the importance of intcrfacial processes, calculated from Eq. (4), are presented. 8 A is taken to be a positive quantity, since it is likely that the activation energy for intracrystalline diffusion is smaller than the activation energy for exit from the pores [35]. It is clear from these figures that at high temperatures, for small values of 8 A or for large crystal thicknesses, surface processes are less important. 

Effect of the activation energy for the forward reaction on the effectiveness factor when the temperature dependence of effective intrapeUet diffusion coefficients is neglected in the mass transfer equation. 

To illustrate the combined effects of the activation energy and frequency factor on the rate of the particular pyrolysis step, the values were calculated for the samples K and KOR at several temperatures in the region 723-823 K (450-550 °C). Comparison of the results demonstrates that at 723 K, for the sample K is two orders of magnitude lower than for sample KOR. This implies relatively slow production of the intermediate B2... 

U ] Rettner C T and Stein H 1987 Effect of the translational energy on the chemisorption of N2 on Fe(111) activated dissociation via a precursor state Phys. Rev. Lett. 59 2768... 

In contrast to the influence of velocity, whose primary effect is to increase the corrosion rates of electrode processes that are controlled by the diffusion of reactants, temperature changes have the greatest effect when the rate determining step is the activation process. In general, if diffusion rates are doubled for a certain increase in temperature, activation processes may be increased by 10-100 times, depending on the magnitude of the activation energy. 

The promotor effect of SO2 increases with the amount added to the reaction medium (Fig.3). An effect of the addition of sulfur dioxide has also been observed on the oxidation of decane with an increase of the activation energy expected for such a poisoning. This addition leads to a noticeable decrease of the rate of oxidation at low temperature, where Cu sulfate is stable, but the effect becomes negligible at about 600 K. At this temperature, the conversion of decane estimated by the evolution of the peak e/m = 57, characteristic of the hydrocarbon, is close to 100% with CufTi02 catalysts in presence or not of SO2 (Figure 4). With Cu/Zr02 SO2 inhibits decane oxidation below 640 K. At 640 K a conversion of about 60% is observed in both the presence or absence of additive and an acceleration of oxidation is noticed at higher temperatures. 

It hag been shown that transition of a backbone carbon from the sp to sp state is promoted by tensile stresses and inhibited by compressive strains (10,44). The acceleration of the process of ozone oxidation of the polymers under load is not associated with the changes in supramolecular structure or segmental mobility of the chain. The probably reason of this effect is a decreasing of the activation energy for hydrogen abstraction (44). The mechanism of initial stages of the reaction of ozone with PP can be represented as ... 

The polar effect involved in radical addition has been repeatedly discussed in the scientific literature. The parabolic model opens up new prospects for the correct estimation of the polar effect (see Section 6.2.7). It permits one to determine the contribution of this effect to the activation energy using experimental data. This contribution (AE ) is estimated by choosing a reference reaction that involves the same reaction center but in which one or both reactants... 

Contribution of the Polar Effect Ato the Activation Energy of the Addition of Polar Radicals to Polar Monomers CH2=CRY (Calculated from the Data of Several Studies [40,51-53])... 

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