A reaction mechanism is a step-by-step description of how a chemical reaction occurs at the molecular level. It outlines the sequence of events, including the breaking and forming of bonds, that lead to the transformation of reactants into products. Understanding these mechanisms helps chemists predict the outcomes of reactions and design new ones. Each step in a reaction mechanism is called an elementary reaction, and these can involve the collision of molecules, the rearrangement of atoms, or the transfer of electrons. By studying mechanisms, scientists can gain insights into related topics such as catalysis, reaction rates, and organic chemistry.