Food is broken down into simpler substances during digestion through processes such as mechanical chewing and enzymatic reactions in the stomach and intestines.

The main source of energy for the human body is carbohydrates. When consumed, carbohydrates are broken down into glucose, which cells use for energy through cellular respiration.

Exothermic chemical reactions are reactions in which heat is released along with the formation of products.

One example is the reaction between magnesium and oxygen to form magnesium oxide, which releases heat and is both a combination reaction and exothermic.

The release of heat in a reaction mixture warms it up, altering its temperature. This thermal energy is a result of the exothermic nature of the reaction, where heat is produced during the formation of products.