Science, Tech, Math › Science Oxidation Reduction Reactions—Redox Reactions The Increase or Decrease in Oxidation Numbers Share Flipboard Email Print Iron oxidizes to form the iron oxide known as rust. Raf Willems / 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 December 09, 2019 This is an introduction to oxidation-reduction reactions, also known as redox reactions. Learn what redox reactions are, get examples of oxidation-reduction reactions, and find out why redox reactions are important. What Is an Oxidation-Reduction or Redox Reaction? Any chemical reaction in which the oxidation numbers (oxidation states) of the atoms are changed is an oxidation-reduction reaction. Such reactions are also known as redox reactions, which is shorthand for reduction-oxidation reactions. Oxidation and Reduction Oxidation involves an increase in oxidation number, while reduction involves a decrease in oxidation number. Usually, the change in oxidation number is associated with a gain or loss of electrons, but there are some redox reactions (e.g., covalent bonding) that do not involve electron transfer. Depending on the chemical reaction, oxidation and reduction may involve any of the following for a given atom, ion, or molecule: Oxidation involves the loss of electrons or hydrogen OR gain of oxygen OR increase in oxidation state.Reduction involves the gain of electrons or hydrogen OR loss of oxygen OR decrease in oxidation state. Example of an Oxidation-Reduction Reaction The reaction between hydrogen and fluorine is an example of an oxidation-reduction reaction: H2 + F2 → 2 HF The overall reaction may be written as two half-reactions: H2 → 2 H+ + 2 e− (the oxidation reaction) F2 + 2 e− → 2 F− (the reduction reaction) There is no net change in charge in a redox reaction so the excess electrons in the oxidation reaction must equal the number of electrons consumed by the reduction reaction. The ions combine to form hydrogen fluoride: H2 + F2 → 2 H+ + 2 F− → 2 HF Importance of Redox Reactions The electron transfer system in cells and oxidation of glucose in the human body are examples of redox reactions. Oxidation-reduction reactions are vital for biochemical reactions and industrial processes as well. Redox reactions are used to reduce ores to obtain metals, to produce electrochemical cells, to convert ammonia into nitric acid for fertilizers, and to coat compact discs.