What is the main characteristic of an exothermic reaction?

An exothermic reaction is characterized by the release of energy, specifically in the form of heat, during the process. This release occurs because the total energy of the products is lower than that of the reactants; thus, energy is expelled to the surroundings. This is a common feature in various chemical reactions, such as combustion, respiration, and many oxidation reactions, where the energy released can often be felt as an increase in temperature.

The nature of exothermic reactions allows them to increase the temperature of their environment, which is why we often observe warmth from burning coal or wood, for instance. This characteristic contrasts sharply with other types of reactions. In an endothermic reaction, energy must be absorbed, typically resulting in a decrease in surrounding temperature. Thus, the identification of the process as exothermic is crucial because it helps in understanding heat transfer in chemical thermodynamics and practical applications like calorimetry.