What occurs when two or more molecules interact and the molecules change into a new substance?

When two or more molecules interact and change into a new substance, a chemical reaction occurs. During this process, the bonds between atoms in the reactant molecules are broken, and new bonds are formed to create different products. This transformation typically involves the rearrangement of atoms and can result in the release or absorption of energy. The new substance formed usually has distinct physical and chemical properties compared to the original molecules.