What defines a chemical reaction?

A chemical reaction is defined as a process in which substances, known as reactants, undergo a transformation to produce different substances called products. This fundamental change is characterized by the breaking and forming of chemical bonds, leading to alterations in the molecular structure and composition of the initial substances.

While changes in physical states, combinations forming compounds, and energy absorption can occur during various processes, they do not encompass the broader scope of what a chemical reaction entails. For instance, a change in physical state involves transitions like solid to liquid (melting) without altering the chemical identity of the substance. Similarly, while a combination of elements to form a compound is a chemical process, it is not representative of the diverse transformations that define a chemical reaction as a whole. Energy absorption can also occur in physical changes and is a specific aspect of some reactions, but it does not capture the essence of the process itself.

Thus, the process of substances transforming into different chemical substances is the most comprehensive and accurate definition of a chemical reaction.