A chemical change is a process in which reactants are change into one or more different products. A chemical change occurs whenever compounds are formed or decomposed. During this reaction, there is a rearrangement of atoms that makes or breaks chemical bonds. This change is usually not reversible, unlike physical changes, which typically are reversible. In short, chemical change is a change of one substance into another substance (i.e. a new substance is formed). By contrast, no new substance is formed in a physical change (for example, the melting of ice is a physical change because when ice changes into water, no new substance is formed.)