What is the difference between a unimolecular and a bimolecular elementary reaction? drag the terms on the left to the appropriate blanks on the right to complete the sentences. 1. a unimolecular elementary reaction involves a single molecule ; the activated complex is derived from only one reactant molecule. a bimolecular elementary reaction involves two reactant molecules; the activated complex is derived from the overall process. only one reactant molecule returned previous answersrequest answer incorrect; try again; 3 attempts remaining you filled in 2 of 4 blanks incorrectly.