An alternative to the concept of variable activation energy
Peter Šimon, Tibor Dubaj, Zuzana Cibulková
Abstract
Abstract It is demonstrated here that the concept of variable activation energy is mathematically not fully correct. Further it is shown that general rate equation is a formal mathematical tool for the description of thermoanalytical kinetic data. The temperature function, k ( T ), is not the rate constant in general and the conversion function, f ( α ), may not reflect the mechanism in case of complex processes. Both, k ( T ) and f (α), are functions enabling to describe the kinetic hypersurface. For the complex processes, the physical meaning of parameters occurring in both functions is unclear. Hence, no mechanistic conclusions should be drawn from the values of an individual kinetic parameter; particularly, just from the values of activation energy. The conclusions can be drawn from the quantities with a clear physical meaning such as the values of isoconversional times, isoconversional temperatures, conversion, reaction rate, etc., i.e., the quantities that can be accessible experimentally. These quantities can be recovered and modeled from known kinetic parameters. It is proved here that the right temperature function may not be necessarily the Arrhenius equation for a complex process.