AAT Bioquest

Is energy always released or absorbed during a chemical reaction?

Posted May 13, 2022


Yes, energy is always either released or absorbed during a chemical reaction. This is because all chemical reactions involve energy. In any chemical reaction, energy is required to break the bonds in reactions, and energy is released when new bonds form after the reaction. Energy is released in exothermic reactions whereas energy is absorbed in endothermic reactions. 

  • Examples of exothermic reactions where energy is released include combustion, rain or ice formation, rusting iron, and explosions. 
  • Examples of endothermic reactions where energy is absorbed include melting ice, evaporation, photosynthesis, and splitting a gas molecule.

Regardless of the type of chemical reaction, and whether it releases or absorbs energy, there is no overall change in the amount of energy during the reaction. Energy may change form during the reaction, for example when gas burns in a furnace, chemical energy changes to heat energy. However, the amount of energy after the reaction is the same as the amount of energy before the reaction. This is in accordance with the Law of Conservation, which states that matter cannot be created or destroyed. 

Additional resources

Structure and energy transfer in photosystems of oxygenic photosynthesis

Amplite™ Colorimetric Aspartate Aminotransferase (AST) Assay Kit