What is characteristic of an exothermic reaction?

An exothermic reaction is characterized by the release of thermal energy into its surroundings. During this type of reaction, the total energy of the products is less than that of the reactants, resulting in the excess energy being emitted, often in the form of heat. This heat release can lead to a noticeable increase in temperature of the surrounding environment.

For example, the combustion of fuels is a classic illustration of an exothermic reaction. When fuels burn, they release heat, making the reaction feel warm to the touch. This release of energy is crucial in many practical applications, including heating systems and engines.

The other options do not accurately describe exothermic reactions. An endothermic reaction, on the other hand, is defined by its absorption of thermal energy, which is not characteristic of exothermic processes. Requiring electricity is not a defining feature of exothermic reactions, as many such reactions occur spontaneously without external energy input. Finally, while exothermic reactions can indeed involve a single reactant, they often also involve multiple reactants, making this description too limited to be characteristic. Thus, the core feature of exothermic reactions lies in their ability to release heat.