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 combustion, such as burning wood or fossil fuels, and the reaction of sodium with chlorine to form sodium chloride. In these reactions, the surroundings often become warmer as energy is released. Exothermic reactions are important in various applications, including heating systems and energy production. Understanding these reactions helps in fields like chemistry, engineering, and environmental science.