Correlation with activation energy

The earlier values for Er and Eqx are retained in the subsequent discussion of the sensitizing and desensitizing properties of dyes to conform to the earlier literature. The general conclusions would not be changed by using Lenhart s values, except for the quantitative correlation with activation energies of sensitization referred to in Section X. 

Taft s constants were used as molecular descriptors to correlate with activation energy and kinetic rates, respectively. They were used because they describe the inductive effects of the substituents in aliphatic compounds. Taft s constant showed a poor correlation (r2 = 0.68) for aliphatic compounds however, the correlation between activation energy and Taft s constant was... 

Activity does not correlate with activation energy. This indicates that microheterogeneity cannot by explained in terms of differences in the ability of individual molecules to reduce the activation energy. Thus other sources of heterogeneity must exist. 

Failure to give a product because of diffusion away of a reactant may give rise to kinetic competition between two processes reaction with activation energy E and diffusion with activation energy Ej- This competition can easily be handled using assumed first-order kinetics (for correlated pairs of reactants) and considering the fraction, F, of the available reaction sites which lead to products within infinite time compared to the fraction, — F, which give no reaction—presumably by diffusion away of a reactant. This treatment leads to the expression... 

Activation energies for bimolecular reactions have been correlated with bond energy data by the use of the Hirschfelder rules (19). 

As part of a multi-technique investigation (see also discussion under mid-infrared spectroscopy later), Corrales et al. [13] plotted the carbonyl index for films prepared from three grades of polyethylenes a high-density PE (HDPE), a linear low-density PE (LLDPE) and a metallocene PE (mPE) (see Figure 5). In this study, the data trend shown in Figure 5 correlated well with activation energies derived from the thermal analysis, which showed that the thermal-oxidative stability followed the order LLDPE > mPE > HDPE, whereas the trend... 

Aromatic substitution patterns have been correlated fairly successfully with activation energies... 

In the temperature range between room temperature and 250°C, and with high surface area samples, behaviour intermediate between surface exchange and bulk diffusion has been observed by two sets of workers [90, 99] who obtained essentially similar results. As the temperature is raised, the second, third and fourth layers can be observed to exchange separately with activation energies of about 0.56—0.78 eV for the second layer, 1.17 for the third layer, and for the fourth layer either a similar value to the third [90] or a value close to the bulk diffusion activation energy of 1.61 eV [99]. The depth to which the solid behaves significantly differently from bulk properties correlates quite well with the... 

FIG. 18.11 Correlation of activation energy for diffusion in polystyrene with molar volume for temperature range Tg < T. 

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. 

Assuming the Polanyi and Semenov correlation between activation energy and bond strength is correct, Johnston and Woolfolk use results on F2 reacting with NO and NO2 to estimate the bond dissociation energy in XeF. They calculate for... 

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