What is a reaction that absorbs energy called?

A reaction that absorbs energy is termed an endothermic reaction. During an endothermic process, energy is taken in from the surroundings, often in the form of heat. This results in a decrease in the temperature of the surrounding environment as the reactants gain energy, which is used to break bonds or form new ones.

Endothermic reactions are characterized by their positive enthalpy change (ΔH), indicating that energy is added to the system. Common examples of endothermic reactions include photosynthesis, where plants absorb sunlight to convert carbon dioxide and water into glucose and oxygen, and the melting of ice, which requires heat to transform solid ice into liquid water.

In contrast, exothermic reactions release energy into the environment, generally resulting in an increase in temperature. Catalytic reactions refer to processes where a catalyst is used to increase the reaction rate without being consumed, while redox reactions involve the transfer of electrons between substances, defining oxidation and reduction processes without specifically indicating energy absorption or release.