What is a chemical reaction?

A chemical reaction is best defined as a process that involves the rearrangement of molecular or ionic structures. During a chemical reaction, the atoms and molecules of the reactants interact, and through the breaking and formation of chemical bonds, new substances are created. This fundamental rearrangement results in products that have different chemical properties from the original reactants.

Understanding this concept is crucial because it highlights that a chemical reaction is not simply a physical change—or merely a change in state or temperature—but involves a transformation at the molecular or atomic level. This differentiation is vital in chemistry, as distinguishing between physical and chemical changes is fundamental when studying the behavior of matter.

Other options may describe certain aspects of reactions or changes in substances but do not encapsulate the complete definition of a chemical reaction. For instance, changes in temperature or physical states alone do not involve new substances being formed, therefore failing to capture the essence of what a chemical reaction entails.