(26c) Mechanism-Free Chemical Engineering Kinetics

Einstein is quoted as saying that Thermodynamics is the only scientific discipline that will remain unchanged through the millennia.  Why so for Thermodynamics and not for the other scientific disciplines?  The answer is simple: Thermodynamics does not depend on mechanism.  All the other scientific disciplines depend upon hypothesizing a mechanism then comparing experimental results to the results produced by the proposed mechanism.  With time, the proposed mechanism changes: it is either discarded for more relevant ones or it is modified to explain new data or more precise data.  The best example of how mechanisms change is the atomic model during the first three decades of the 20^thCentury.

            Atomic physics went from detailed planetary models to mathematical representations of changes of state, which is essentially what Thermodynamics does.  Thermodynamics presents mathematical methods for describing changes of state for materials.  In other words, Thermodynamics is mechanism-free.

            The same cannot be said for chemical kinetics.  Currently, we guess a mechanism for a chemical reaction, then compare experimental data to the datum generated by our assumed mechanism.  If the correlation is “good”, then we assume the mechanism is correct and we use it to design a chemical plant.  However, there is no proof that the assumed mechanism is correct.

            Today’s computer power and user-friendly software provide us with the tools to possibly remove mechanism from chemical kinetics.  This paper discusses the issues involved in freeing chemical kinetics from mechanism.