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The Arrhenius equation is usually applied to express the dependence of reaction rate on temperature. Laidler gave a brief historical account of the development of this equation, beginning with the pioneer work of Wilhelmy, who in 1850 was the first to propose an equation relating the reaction rate constant to temperature (1). Pacey showed that the main focus of the Arrhenius law, the activation energy (E^sup a^), is not a single quantity but a composite quantity even for a single reaction. The reaction chosen for detailed study was
D+H^sub 2^ --> DH + H
and the author compared different interpretations of E^sub a^ for this simple reaction (2). Later Logan discussed ways in which the status of the Arrhenius equation has changed since it was first proposed. He pointed out that in many instances "the Arrhenius activation energy" is a quantity with no (not even approximate) physical significance (3). Olah discussed the relationship between Arrhenius' threshold energy and the phenomenologically defined "effective activation" energy which "lacks a clear thermodynamic interpretation" (4).
Yet not only chemists but many scientists from other disciplines do apply a simple Arrhenius law to their results and thus obtain the so-called "effective" (or "apparent") value of E^sub a^. Then, basing their discussion on its value, they can speculate about a mechanism for the process involved or simply extrapolate the data to new conditions. In this connection it is necessary to mention some "unconventional applications of the Arrhenius law" (5). Laidler demonstrated how it could be applied to such phenomena as chirping of tree crickets (E^sub a^ = 51 kJ/mol), creeping of ants (108 kJ/mol below 16 deg C and 51 kJ/mol above that temperature), flashing of fireflies (51 kJ/mol), rate of terrapin heartbeat (77 kJ/mol from 18 to 34 deg C and much higher below 18 deg C), human alpha brain-wave rhythm (about 30 kJ/mol), and even human rates of counting and forgetting (100 kJ/mol for both). J. A. Campbell, the author of a remarkable popular book on chemical kinetics (6), presented other examples in his Eco-chem column in this Journal (7). The heartbeat rate of the water flea Daphnia increases with the temperature (E^sub a^ = 50 kJ/mol). A...