What process typically occurs in an exothermic reaction?

In an exothermic reaction, the primary characteristic is the release of heat to the surroundings. This occurs when the total energy of the reactants is higher than that of the products, which means that as the reaction progresses, energy is released in the form of heat. This release can cause a rise in temperature of the surrounding environment.

In contrast, absorption of heat is a defining feature of endothermic reactions, where energy is taken in from the surroundings to proceed. The formation of new solids or gases can happen in various types of reactions, but these processes do not specifically define exothermic reactions. Furthermore, the formation of gases at constant temperature does not inherently relate to the characteristics of exothermic processes. Thus, the primary and defining aspect of an exothermic reaction is indeed the release of heat.