Chemical reactions that release energy are described by Education.com as exothermic reactions, and their equations follow the form: reactants = products + energy. Examples of exothermic reactions are explosions, such as fireworks, or combustion, such as with engines. The reactants of exothermic reactions contain stored energy which is then released as exothermic heat once the chemical reaction has occurred, states Scientific American.
GCS Science tells us that the majority of chemical reactions are exothermic; however, chemical reactions that take in energy are called endothermic reactions. Exothermic reactions release energy usually in the form of heat but also in other forms such as light, electricity or sound. Additional examples of chemical reactions that release energy, given by Princeton Education, are rain condensation; fuel combustion of coal or oil; burning of wood; mixing water and strong acids; and the setting of cement. The most well-known endothermic reaction is photosynthesis, which takes in light energy from the sun, while the most well-known exothermic reaction is cellular respiration, which releases energy in the form of ATP along with all the oxygen that we breathe. About.com gives an example of sodium mixed with chlorine as an exothermic reaction to release energy and yield table salt.