Science, Tech, Math › Science Heat of Formation Definition - Chemistry Glossary Share Flipboard Email Print Heat of formation refers to the energy released or absorbed when a pure substance forms from its elements. Kwanchai Lerttanapunyaporn / EyeEm, Getty Images Science Chemistry Basics Chemical Laws Molecules Periodic Table Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated June 06, 2019 In chemistry, heat of formation is the heat released or absorbed (enthalpy change) during the formation of a pure substance from its elements at constant pressure (in their standard states). Heat of formation is usually denoted by ΔHf. It is typically expressed in units of kilojoules per mole (kJ/mol). Heat of formation is also called enthalpy of formation. The pure substances in question may be elements or compounds. However, the heat of formation of a pure element has a value of 0. Sources Kleykamp, H. (1998). "Gibbs Energy of Formation of SiC: A contribution to the Thermodynamic Stability of the Modifications". Berichte der Bunsengesellschaft für physikalische Chemie. pp. 1231–1234.Zumdahl, Steven (2009). Chemical Principles (6th ed.). Boston. New York: Houghton Mifflin. pp. 384–387. ISBN 978-0-547-19626-8.