What effect does an exothermic reaction have on the surrounding environment?

An exothermic reaction is characterized by the release of energy, primarily in the form of heat, into the surrounding environment. This release of heat raises the temperature of the surroundings and can lead to noticeable effects, such as warming of nearby materials or the air. As a result, if you observe an increase in temperature during a chemical reaction, it is likely that the reaction is exothermic.

The phenomenon of heat being released is central to the concept of exothermic processes, such as combustion and many types of chemical reactions where energy is given off as products are formed. Thus, the correct understanding is that exothermic reactions contribute to an increase in the thermal energy of their environment.