Unimolecular Reaction: A unimolecular reaction is an elementary step that involves the transformation of one molecule into products. For example, the decomposition of hydrogen peroxide (H2O2) into water and oxygen gas.
Bimolecular Reaction: A bimolecular reaction is an elementary step that involves the collision between two molecules or species to form products. An example would be the combination of hydrogen gas (H2) with chlorine gas (Cl2) to produce hydrogen chloride (HCl).
Elementary Step:An elementary step refers to an individual chemical process in a reaction mechanism. It represents a single molecular event and may involve one or more molecules colliding or breaking apart.