Britannica Sources used in this answer

Why can kinetic evidence disprove a proposed reaction mechanism without proving another mechanism with complete certainty?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

dissociation of E–N — reaction mechanism Possible energy diagram for the dissociation of a covalent molecule, E–N, into its ions E⁺ and N⁻ (see text).

In the study of chemical kinetics, kinetic evidence is a powerful tool for investigating reaction mechanisms, but it is inherently limited in its ability to confirm a pathway with absolute certainty.

Why Kinetic Evidence Cannot Prove a Mechanism

While kinetic measurements can demonstrate that a proposed mechanism is consistent with observed data, they cannot prove it is the only possible explanation. For any given set of kinetic data, it is often possible to devise multiple, more complex schemes that would yield the same results. Consequently, scientists generally accept the simplest mechanism that accounts for the observed kinetic behavior until further evidence—such as the detection of reaction intermediates—suggests otherwise.1

Why Kinetic Evidence Can Disprove a Mechanism

Conversely, kinetic evidence is highly effective at disproving a proposed mechanism. A fundamental requirement for any valid mechanism is that it must accurately account for the overall kinetic behavior of the reaction, specifically how the reaction rate depends on reactant concentrations. If the experimental kinetic data contradicts the predictions derived from a proposed mechanism, that mechanism can be definitively rejected.12

Ultimately, while an investigation can disprove a mechanism, it can never establish one with absolute certainty.2