Which of the following best describes an exothermic reaction?

An exothermic reaction is characterized by the release of energy, typically in the form of heat, which results in an increase in the temperature of the surroundings. In this type of reaction, the reactants have more stored energy compared to the products. When the reaction occurs, energy is released to the environment, leading to a warming effect. This release of energy is a defining feature of exothermic processes.

For example, combustion reactions, such as burning fuel, are common exothermic reactions where heat and often light are produced, making the environment around the reaction feel warmer. Therefore, the statement that indicates the surroundings become hotter accurately captures the essence of an exothermic reaction.

Other descriptions do not align with this definition; for instance, absorbing energy would indicate an endothermic reaction where surroundings cool down, and stating that the energy change is zero conflicts with the inherent nature of exothermic reactions that involve energy release. Additionally, forming gas at high temperatures does not specifically convey the concept of energy release; it could apply to various reaction types regardless of whether they are exothermic or endothermic.