Arrhenius parameters, decompositions solids

Trillo et al. (47,137) have reported compensation behavior in oxide-catalyzed decomposition of formic acid and the Arrhenius parameters for the same reactions on cobalt and nickel metals are close to the same line, Table V, K. Since the values of E for the dehydration of this reactant on titania and on chromia were not influenced by doping or sintering, it was concluded (47) that the rate-limiting step here was not controlled by the semiconducting properties of the oxide. In contrast, the compensation effect found for the dehydrogenation reaction was ascribed to a dependence of the Arrhenius parameters on the ease of transfer of the electrons to the solid. The possibility that the compensation behavior arises through changes in the mobility of surface intermediates is also mentioned (137). 

Kinetic parameters. The hterature contains numerous reports of the rate equations identified for particular crystolysis reactions, together with the calculated Arrhenius parameters. However, reproducible values of (Section 4.1.) have been reported by independent researchers for relatively few solid state decompositions. Reversible reactions often yield Arrhenius parameters that are sensitive to reaction conditions and can show compensation effects (Section 4.9.4.). Often the influences of procedural variables have not been carefully identified. Thus, before the magnitudes of apparent activation energies can be compared, attempts have to be made to relate these values to particular reaction steps. 

Introduction Dehydrations of metal hydroxides are attractive model reactions for basic studies of the kinetics of solid-state reactions and these reactions are widely used for the commercial production of metal oxides [45]. However, as shown in the recent paper by L vov and Ugolkov [55], available data on the reaction mechanisms and kinetics are inconsistent. For example, the parameter E for the dehydration of Mg(OH)2, reported in different papers, varies from 53 to 372 kJ mol One of the factors responsible for the large scatter of the E values estimated from Arrhenius plots is the low precision and accuracy of this method, especially as applied to decomposition to gaseous and solid products. The results obtained in [55[ by the third-law method, as indicated below, are much more reliable. 

In the field of chemical kinetics the KCE was first pointed out by Zawadski and Bretsznayder [571] while studying the thermal decomposition of CaCOs under various pressure of CO2 (Ea Pco2 ) but in the field of solid state physics it was often called the thermodynamic compensation rule [569], originally derived upon conductivity studies on various oxides [575]. In the field of non-isothermal studies it was first noticed through the mathematical interplay between the kinetic parameters A and E by Sestdk [574].. Early studies pointed that non-linearity in the Arrhenius plots gives the evidence of a complex process [3, 566, 570], that the mathematical correlation of the exponential pre-factor and... 

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