Advanced Placement (AP) Chemistry Practice Exam 2026 - Free AP Chemistry Practice Questions and Study Guide

An endothermic reaction is characterized by the absorption of heat from the surroundings. In an endothermic process, energy is required for the reaction to occur, which typically results in a decrease in the temperature of the surrounding environment as the system takes in thermal energy. This energy input is necessary to break bonds in the reactants, allowing for the formation of products.

While some reactions can be spontaneous, spontaneity does not directly correlate with whether a reaction is endothermic or exothermic. Additionally, endothermic reactions can occur over a range of temperatures rather than at a fixed temperature, as they are influenced by factors such as concentration, pressure, and temperature changes. Thus, the key defining feature of an endothermic reaction is its ability to absorb heat from the surroundings, highlighting the energy requirement for the reaction to proceed.