What is the best description of a chemical reaction?

The best description of a chemical reaction is that it is a process that changes one set of chemicals into another set of chemicals. In a chemical reaction, the bonds between atoms in reactants are broken and then reformed to create different substances, known as products. This transformation involves the rearrangement of atoms and can include the release or absorption of energy, leading to observable changes in properties such as color, temperature, or the formation of gases or precipitates.

This definition emphasizes the fundamental aspect of chemical reactions: the identity of the substances before and after the reaction is different due to the rearrangement of atoms. In contrast, options that suggest processes without changes or that describe physical changes are not reflective of the nature of chemical reactions, as they do not involve the transformation of one substance into another.