What is the definition of a chemical reaction?

A chemical reaction is defined as a process that transforms reactants into products. This definition highlights the fundamental aspect of chemical reactions, where substances undergo a chemical change, leading to the formation of new substances with different properties from the original reactants. During a chemical reaction, the bonds between atoms are broken and formed, resulting in the rearrangement of atoms and the creation of new molecules.

This definition sets chemical reactions apart from physical changes, which may involve changes in state or appearance but do not alter the chemical composition of the substances involved. Separating mixtures and combining elements without a reaction do not involve the transformation of substances into new products, thus they do not fit the definition of a chemical reaction. Understanding this distinction is crucial for identifying and classifying different types of processes in chemistry.