Noun | 1. | decomposition reaction - (chemistry) separation of a substance into two or more substances that may differ from each other and from the original substance chemical science, chemistry - the science of matter; the branch of the natural sciences dealing with the composition of substances and their properties and reactions chemical reaction, reaction - (chemistry) a process in which one or more substances are changed into others; "there was a chemical reaction of the lime with the ground water" electrolysis - (chemistry) a chemical decomposition reaction produced by passing an electric current through a solution containing ions |