Arrhenius plots linear

Usually the Arrhenius plot of In k vs. IIT is linear, or at any rate there is usually no sound basis for coneluding that it is not linear. This behavior is consistent with the conclusion that the activation parameters are constants, independent of temperature, over the experimental temperature range. For some reactions, however, definite curvature is detectable in Arrhenius plots. There seem to be three possible reasons for this curvature. 

Above 570°C, a distinct break occurs in the Arrhenius plot for iron, corresponding to the appearance of FeO in the scale. The Arrhenius plot is then non-linear at higher temperatures. This curvature is due to the wide stoichiometry limits of FeO limits which diverge progressively with increasing temperature. Diffraction studies have shown that complex clusters of vacancies exist in Fe, , 0 Such defect clustering is more prevalent in oxides... 

Arrhenius plot. In an Arrhenius plot the ordinate is the log of the material life. The abscissa is the reciprocal of the absolute temperature. The linear curves obtained with the Arrhenius plot overcome the deficiency of most of the standard tests, which provide only one point and indicate no direction in which to extrapolate. Moreover, any change in any aspect of the material or the environment could alter the slopes of there curves. Therein lies the value of this method. 

The time required to produce a 50% reduction in properties is selected as an arbitrary failure point. These times can be gathered and used to make a linear Arrhenius plot of log time versus the reciprocal of the absolute exposure temperature. An Arrhenius relationship is a rate equation followed by many chemical reactions. A linear Arrhenius plot is extrapolated from this equation to predict the temperature at which failure is to be expected at an arbitrary time that depends on the plastic s heat-aging behavior, which... 

Fig. 14. Arrhenius plot of the kinetics of H atom recombination on a rich in copper alloy film catalyst Ni20Cu80. Within the whole range of temperature the linear relationship holds activation energy constant. After Karpinski (65a).

In a more recent paper (Stovpovoi et al., 1991b) Bagal and coworkers interpret their observation that Arrhenius plots of the rates of various N- and C-couplings of aromatic amines (e. g., 1-naphthylamine, 2,6-naphthylaminesulfonic acid, and 4-me-thylaniline) are linear only in aqueous systems, but not in aprotic solvents such as nitromethane or acetonitrile. Their explanation is based on an extension of the clas-... 

The behaviour [821] of AgN02 is closer to that expected of a nitro compound than a nitrite. Decomposition (308—363 K) yields Ag metal and N02. a—Time curves are sigmoid with a prominent linear region (0.15 < a < 0.45) but the Arrhenius plot was curved at >333 K. This was attributed to inadequate gaseous product removal. In contrast to the behaviour observed for most other solids, pre-irradiation with 7-rays inhibits subsequent thermal decomposition [829]. 

Figure 5.1 shows an Arrhenius plot for the reaction O -b N2 NO -b N the plot is linear over an experimental temperature range of 1500 K. Note that the rate constant is expressed per molecule rather than per mole. This method for expressing k is favored by some chemical kineticists. It differs by a factor of Avogadro s number from the more usual k. 

Impregnating AI2O3 with Pt now produces a catalyst. The activity of one gram of catalyst is now measured in a plug-flow reactor under conditions where oxygen is the MARI and the activity is high. It is seen that the rate increases with temperature, but a simple linear relation is not found between ln(r) and l/Tin an Arrhenius plot. 

In order to go further into the experimental check we constructed Arrhenius plots of the fluorescence quantum yield of BMPC in a few solvents (methanol, ethanol, propanol, hexanol and methylene chloride), all of which showed good linearity. The activation energies and A/kp ratios, calculated from the slopes and intercepts of those plots, are collected in Table 1. The smooth increase of both parameters in the alcohol series is mainly associated with the increase of solvent viscosity. On the other hand, decrease of the solvent dielectric constant from 32.7 (methanol) to 8.9 (dichloromethane) causes a small but significant increase of the activation energy also, this increase is probably somewhat compensated by the decrease of the viscous-flow... 

Figure 4. Cross-sectional bright-field TEM views of Au-implanted silica samples at 3 x lO Au /cm, 190 keV, aimealed for 1 h at (a) 400 °C in air, (b) 700 °C in air, (c) 900 °C in air, and (d) 900 °C in Ar, respectively (e) the histograms of the size distribution of the samples annealed 1 h in air at different temperatures (f) Arrhenius plot of the squared average cluster radius after 1 h annealing in air (filled circles) or argon (empty triangles). Solid lines are linear fit to the experimental data.

As described in the previous sections, a stable Pt skin of a few nanometers is formed on the Pt-Fe, Pt-Co, and Pt-Ni alloy surfaces after electrochemical stabilization. Figure 10.12 shows Arrhenius plots of kapp on the alloy electrodes at —0.525 V vs. E° in comparison with that of a pure Pt electrode. In the low temperature region (20-50 °C for Pt54Fe45, 20-60 °C for Pt6gCo32 and Ptg3Ni37), linear relationships between log kapp and 1 / Tare observed at all the electrodes, corresponding to the following Arrhenius equation ... 

Nonlinear Arrhenius Plots For most organic reactions, plots of In k versus l/T are linear, and afford and A values in accord with the Arrhenius equation." However, for systems where QMT is involved, rate constants fall off less steeply than expected as temperatures are lowered, which often leads to upwardly curved Arrhenius plots as illustrated in Figure 10.2 ... 

Transition state statistical treatments predict that for classical reactions. Ah and Ad should be comparable in magnitude, with Ah/Aq > 0.7 approximately. Ratios of A values smaller than this are also indicative of QMT. The relatively smaller than expected measured Ah values can be envisioned to arise from the greater deviation of H-transfers from linear Arrhenius plots at lower temperatures extrapolation to 1/r = 0 then gives a lower intercept corresponding to the apparent A value. ... 

Laser flash irradiation of diazofluorene in perdeuterated matrices, in contrast, gave severely nonexponential decay of the carbene spectra. Analyses of the products formed in the low-temperature matrices showed that, as with the EPR studies, the carbene was not undergoing D-abstraction. LFP of the diazo compound 36 in CFCl3-CF2BrCF2Br glasses gave linear first-order decays, and linear Arrhenius plots, which were attributed to classical Cl and Br abstractions. 

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