National Council of Examiners for Engineering and Surveying (NCEES) Fundamentals of Engineering (FE) Chemical Practice Exam

When a reaction absorbs heat, it is classified as endothermic. In an endothermic reaction, the system takes in energy from the surroundings, usually in the form of heat, leading to a decrease in the temperature of the environment or the reaction mixture itself. This energy input is required for the reactants to convert into products, often overcoming the activation energy barrier.

In contrast, a reaction at equilibrium does not absorb or release heat overall; it reflects a state where the rates of the forward and reverse reactions are equal. A reaction that generates energy indicates an exothermic process, where heat is released to the surroundings. Exothermic reactions contribute to an increase in temperature of the surroundings, distinguishing them further from endothermic reactions, which absorb heat and decrease the surroundings' temperature. Therefore, the identification of an endothermic reaction correctly aligns with the absorption of heat.