Exothermic reactions are chemical processes that release energy, usually in the form of heat or light. This energy release occurs when the total energy of the products is lower than that of the reactants. Common examples include the combustion of fuels, such as wood or gasoline, and the reaction of sodium with chlorine to form sodium chloride. During an exothermic reaction, the surrounding environment often becomes warmer as energy is transferred from the reaction to the surroundings. These reactions are important in various applications, including thermochemistry, where they help in understanding energy changes, and in everyday life, such as in fireworks and batteries.