A chemical reaction is the change of a substance into a new one that has a different chemical identity. The formation of the mixture, the formation of a solution, or formation of a compound involves a chemical reaction. In a chemical reaction, there are different forms of energy released or formed or released. Example In the thermite reaction, Al reduces Fe2O3 to Fe in an extremely exothermic reaction in which Al is oxidized to Al2O3. The reaction produces enough heat to melt the iron. Because of the extreme heat produced in the thermite reaction, it is used industrially to weld iron. Here heat energy is released. Representation of four basic chemical reactions types: synthesis, decomposition, single replacement and double replacement.