A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Chemical reaction, a process in which one or more substances, the reactants, are converted to one or more different substances, the products. Substances are either chemical elements or compounds. A chemical reaction rearranges the constituent atoms of the reactants to create different substances as products - representation of four basic chemical reactions types: synthesis, decomposition, single replacement and double replacement. Chemical reactions are the processes by which chemicals interact to form new chemicals with different compositions. A chemical reaction is a process where reactants are transformed into products. How chemicals react is dictated by the chemical properties of the element or compound- how a compound or element changes composition.