What does it mean for a reaction to be endothermic?

An endothermic reaction is characterized by the absorption of energy from its surroundings, typically in the form of heat. This process leads to a decrease in temperature of the surrounding environment because the system is taking in heat. When energy is absorbed, the reactants undergo a transformation that requires an input of energy to break bonds and facilitate the reaction.

This is contrasted with exothermic reactions, where heat is released and the surroundings feel warmer. The correct choice highlights the fundamental aspect of endothermic reactions—energy is drawn into the system, enabling reactions that may not occur spontaneously without this energy input.

Other options misrepresent the nature of endothermic reactions. For instance, a reaction releasing heat is indicative of an exothermic process, while the state of matter in which a reaction occurs does not define whether it is endothermic or exothermic. The net energy release is also characteristic of exothermic reactions, not endothermic ones.