89.1 Introduction of Chemical Kinetics (2) Elementary reaction (2) Category of elementary reactions According to the number of molecules (moiety) involved in the reaction, elementary reactions can be divided into three kinds: unimolecular reaction: 12=21 bimolecular reaction: Br+H,=HBr+H termolecular reaction: 2I+H= 2HI Accurate definition and convention(2) Category of elementary reactions According to the number of molecules (moiety) involved in the reaction, elementary reactions can be divided into three kinds: unimolecular reaction: I2 = 2I bimolecular reaction: Br + H2 = HBr + H termolecular reaction: 2I + H2 = 2HI (2) Elementary reaction §9.1 Introduction of Chemical Kinetics Accurate definition and convention