TABLE OF CONTENTS Sometimes, for a series of closely related, but not identical reactions, the experimental Arrhenius parameters, determined by similar procedures, have been reported to conform to an equation of the form:
where a and b are constants. This is known as "a compensation effect" [2], [3], [74], [75] because the decrease in reaction rate resulting from an increase in activation energy, E, is offset by an increase in the magnitude of ln A. This is also known as the isokinetic effect because, for the set of (A, E) values that fit equation (10.5), there exists a temperature, T K, at which all rate coefficients are equal. For many reactions, the value of T K is at, or within, the temperature ranges of the kinetic measurements exhibiting the compensation behaviour. A similar effect has also been observed for a series of closely related, but not identical, experiments on a single chemical reaction, where the differences in the experimental conditions, including the physical state and history of the solid reactant, may result in a relationship of the form of equation (10.5) between the apparent Arrhenius parameters.
A huge volume of literature [75] has grown around this seemingly simple relationship. None of the many theoretical explanations [74] suggested for compensation behaviour has received general acceptance. There are good reasons for suspecting that many reported instances of compensation effects may be computational artefacts [76],
