The changing of substances to other substances by the breaking of bonds in reactants and the formation of bonds in products.

Explanation:

The changing of substances to other substances by the breaking of bonds in reactants and the formation of bonds in products is the definition of chemical change or reaction.

Chemical reactions or cahnges are the transformation of pure substances, compounds or elements, into other substances by the breaking of some bonds adn the formation of other bonds.

The chemical reactions are represented by chemical equations with the reactants in the left side and the products in the right side, connected by  the use of arrows.

For example, the chemical equation CH₄ (g) + O₂(g) → CO₂(g) + H₂O(g) represents the combustion reaction (chemical change) of methane (CH₄) with oxygen (O₂).

The products of the reaction are carbon dioxide (CO₂) and water (H₂O) which are the new substances formed by breaking the chemical bonds in CH₄ and O₂ and the formation of the bonds in the new molecules (CO₂ and H₂O).

Chemical equation: CH₄ (g) + O₂(g)  →  CO₂(g) + H₂O(g)

                                    ↑           ↑               ↑             ↑

                                 -- reactants --         --- products --

The reactants have been transformed into different chemical compounds, so  this is a chemical changle.