Chemical changes are different from physical changes in that they form new substances. When a chemical change occurs, the molecules in the substance(s) are rearranged to form a new product with different chemical properties. This contrasts with physical changes, which do not form new substances and often involve shifts in the phase of matter (such as from solid to liquid or liquid to gas) that are typically reversible without changing the chemical identity of the substance. Physical changes may or may not involve heat, just as chemical changes might, but the defining characteristic of a chemical change is the formation of new substances.
