How is a chemical reaction mechanism defined?

A chemical reaction mechanism is accurately defined as a step-by-step description of the molecular events in a reaction because it delves into the specific pathways through which reactants transform into products. This involves detailing each individual step, including the breaking and forming of bonds, changes in molecular structure, and the intermediate species formed along the way. Understanding the mechanism provides insight into the dynamics of the reaction, such as rates and the role of catalysts, giving a clearer picture of how a reaction proceeds at the molecular level.

The other options, while related to aspects of chemical reactions, do not capture the essence of what a mechanism entails. For instance, energy change diagrams illustrate thermodynamic properties but lack the molecular detail of how changes occur stepwise. Similarly, narratives describing final products focus on outcomes rather than the process itself, and lists of reactants and products typically summarize entities involved without revealing the intricate steps or intermediates that constitute the mechanism.