Activation energy decomposition

The kinetics of reversible decompositions are often highly sensitive to reaction conditions [43]. For example, the values of and E, for the decomposition of CaCOj show unusually wide variations, owing to the sensitivity of reaction rate to the availability of COj [44,45]. The spread of apparent E values is considerable [46] and some values are close to the dissociation enthalpy [1]. However, Beruto and Searcy [47] concluded that, under high vacuum conditions, the constant rate of interface advance in large crystals was probably controlled by the dissociation step in the absence of a perceptible contribution from the reverse process. The decomposition activation energy (205 kJ mol ) was appreciably larger than the dissociation enthalpy (178 kJ mol ). This is probably the most precise kinetic measurement for the calcite decomposition [48]. 

The formate, formed by oxidative dehydrogenation of the acid, is quite stable and doesn t decompose until 480 K. This decomposition is a classical first-order case with a decomposition activation energy of 130 kJ mol-1 and a normal value pre-exponential of 1013 s-1. The great ability of the TPD technique is the separation of the individual steps in the reaction in temperature. It is clear that the step proceeding over the highest barrier in this case is the formate decomposition, and that in a catalytic oxidation of formic acid the most abundant surface intermediate is likely to be the formate with its decomposition being rate determining. 

The homogeneous gas phase exchange reactions of diatomic molecules are described by activation energies that are much lower than the decomposition activation energies. The finding is that isotopic equilibrium is reached under reaction conditions in which the contributions from three centre atom—molecule reactions are negligible. 

In temperature programmed desorption experiments this carbonate species desorbs as CO2 at a peak maximum temperature of 333 K. The desorption/decomposition activation energy, E, ... 

DMA analysis of NR/Ti02 nanocomposites prepared by latex blending showed that its Tg and activation energy are higher than the pure NR. ° According to their dynamic model, the decomposition activation energy of blank sample (vulcanized rubber) and the samples which contained Ti02 with 0.1%, 0.5%, 1.0%, 2.0% were 229.99, 231.085, 201.727, 219.107, 208.249 kJ mol and their pre-exponential factor of dynamic model were found to be 5.07 x 10 8.46 x 10 , 2.94 x 10 8.03 x 10 , 1.04 x 10 s respectively. 

Stereoselective water eliminations in 3- and 4-arylcyclohexanols under electron impact have been examined with activation energies determined as the difference between the appearance potential of a given cation and the ionization potential of the parent molecule. The electron-impact-induced breakdown of phenylcycloalkanes and 1-phenylcycloalkan-l-ols (17) has been related to ring strain. In these decompositions activation energies increased with increasing ring size. Mass spectrometry of the epimeric 5-methylcyclohexane-l,3-diols (18a, and b) and their... 

Kinetics of the aralkyl hydroperoxides decomposition in the presence of tetraethylammonium bromide (Et NBr) has been investigated. Et NBr has been shown to reveal the catalytic properties in this reaction. The use of Et- NBr leads to the decrease up to 40 kJmol of the hydroperoxides decomposition activation energy. The complex formation between hydroperoxides and Et NBr has been shown by the kinetic and H NMR spectroscopy methods. Thermod5aiamic parameters of the complex formation and kinetic parameters of complex-bonded hydroperoxides have been estimated. The model of the reactive hydroperoxide - catalyst complex structure has been proposed. Complex formation is accompanied with hydroperoxide chemical activation. 

Symbate changes in thermolysis and cataljlic decomposition activation energies are observed for considered aralkyl hydroperoxides (Fig. 3). Thus peroxide bond cleavage causes the activation energy of the complex-bonded hydroperoxide decomposition. 

FIGURE 3 Symbate changes in thermolysis (Ef"") and catalytic (E ) decomposition activation energies of aralkyl hydroperoxides (E values are listed elsewhere [14]). 

Keywords MAX phases, thermal stability, decomposition, activation energy. 

Thermal decomposition activation energies and products Glass transition temperature Tg (T) See also corresponding chapter of this Handbook 85-104 Various data cited in the 3/e of Polymer Handbook 95... 

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