I already answered this question in Spanish language. Now I answer in English.
Answer: the chemical changes.
Explanation:
We understand by composition of a substance to the proportion (ratio or percentage) of each element (type of atoms) that makes up the same, as well as the way in which these elements are linked (chemical bonds).
A chemical change is a process, also called a chemical reaction, in which one or more substances are converted into different substances.
The resulting substances are different because their composition is different, since some chemical bonds have been broken and others have been formed, giving rise to a new structure. The chemical formula of each compound product of the chemical change will present a different combination of atoms, in ratio or structure.
