A chemical reaction is a process in which substances, called reactants, undergo a transformation to form different substances, called products. During a chemical reaction, the bonds between atoms in the reactants are broken, and new bonds are formed to create the products. This process involves changes in the chemical composition and properties of the substances involved. Chemical reactions can be classified into various types, such as synthesis, decomposition, single replacement, double replacement, and combustion. They are fundamental to many natural and industrial processes, including metabolism, combustion, and the production of materials and chemicals.