Science, Tech, Math › Science Exothermic Reaction Definition What Is an Exothermic Reaction? Share Flipboard Email Print The rusting of steel is an example of an exothermic chemical reaction. Pixabay Science Chemistry Chemical Laws Basics 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 January 16, 2020 An exothermic reaction is a chemical reaction that produces heat (has a negative ΔH). In other words, the activation energy needed to initiate the reaction is less than the energy it releases. Examples of exothermic reactions include neutralization reactions, the Haber process, the thermite reaction, and combustion reactions. The opposite of an exothermic reaction is an endothermic reaction. Endothermic reactions absorb more heat from their surroundings than they release. Exothermic and endothermic reactions are types of exergonic and endergonic reactions. In exergonic and endergonic reaction, the net energy (whether it be heat, light, or sound) is greater (exergonic) or less (endergonic) than the energy needed for the reaction to proceed.