Science, Tech, Math › Science What Is Fire Made Of? The Chemical Composition of Fire Share Flipboard Email Print Christopher Murray / EyeEm / Getty Images Science Chemistry Physical Chemistry Basics Chemical Laws Molecules Periodic Table Projects & Experiments Scientific Method Biochemistry 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. Anne Marie Helmenstine, Ph.D. Facebook Twitter 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. Learn about our Editorial Process Updated on June 04, 2022 What is fire made of? You know that it generates heat and light, but have you ever wondered about its chemical composition or state of matter? What Is Fire Made Of? A flame is a mixture of its fuel, light, and the solids and gases that both form the fire and are produced by it. Incomplete combustion produces soot, which is mainly carbon.Fire is mostly a state of matter called plasma. However, parts of a flame consist of solids and gases.The exact chemical composition of fire depends on the nature of the fuel and its oxidizer. Most flames consist of carbon dioxide, water vapor, nitrogen, and oxgen. Chemical Composition of Fire Fire is the result of a chemical reaction called combustion. At a certain point in the combustion reaction, called the ignition point, flames are produced. Ordinarily, flames consist primarily of carbon dioxide, water vapor, oxygen, and nitrogen. In the usual combustion reaction, a carbon-based fuel burns in air (oxygen). Potentially, fire only contains gases from the fuel, carbon dioxide, water, nitrogen, and oxygen. However, incomplete combustion yields a host of other possibilities. Soot is a primary component of incomplete combustion. Soot mainly contains carbon, but various organic molecules may occur. Other gases found in fire include carbon monoxide and sometimes nitrogen oxides and sulfur oxides. A candle flame consists of vaporized water, carbon dioxide, water, nitrogen, oxygen, soot hot enough that it is incandescent, and light/heat from the chemical reaction. Fire Without Oxygen However, fire does not actually require oxygen. Yes, the oxidizer most often encountered is oxygen, but other chemicals also work. For example, burning hydrogen with chlorine as an oxidizer also produces a flame. The product of the reaction is hydrogen chloride (HCl), so the fire consists of hydrogen, chlorine, HCl, light, and heat. Other combinations are hydrogen with fluorine and hydrazine with nitrogen tetroxide. State of Matter of Fire In a candle flame or small fire, most of the matter in a flame consists of hot gases. A very hot fire releases enough energy to ionize the gaseous atoms, forming the state of matter called plasma. Examples of flames that contain plasma include those produced by plasma torches and the thermite reaction. The main differences between gases and plasma are the distance between particles and their electrical charge. Gases consists of molecules, atoms, and ions that are widely spaced. The distance between particles is much greater in plasma. Additionally, the particles in plasma are almost exclusively charged particles (ions). Why Fire Is Hot Fire emits heat and light because the chemical reaction that produces flames is exothermic. In other words, combustion releases more energy than is needed to ignite or sustain it. In order for combustion to occur and flames to form, three things must be present: fuel, oxygen, and energy (usually in the form of heat). Once energy starts the reaction, it continues so long as fuel and oxygen are present. Cold Fire While all fire produced heat or is exothermic, some fires are cooler than others. So-called cold fire refers to a fire that burns below a temperature of about 400 °C (752 °F). At this temperature, the flame of the fire is invisible, yet the reaction proceeds. While cold fire is fairly uncommon on Earth, scientists have produced it in space. In a microgravity environment, fire burns with a spherical flame. Cold fire burns differently from regular combustion. Normally, the heat of a fire (and gravity) push combustion products away from the reaction. In a cool flame, these products stay within range of the reaction and participate further. Ultimately, a cold fire can burn away its waste products. On Earth, cooler flames come from certain volatile fuels. For example, alcohol produces a cooler flame than acetylene. The availability of oxygen also matters. When oxygen is limited, so is the reaction, making the fire cooler. Sources Bowman, D. M. J. S.; et al. (2009). "Fire in the Earth system". Science. 324 (5926): 481–84. doi:10.1126/science.1163886Lackner, Maximilian; Winter, Franz; Agarwal, Avinash K., eds. (2010). Handbook of Combustion, 5 volume set. Wiley-VCH. ISBN 978-3-527-32449-1.Law, C.K. (2006). Combustion Physics. Cambridge, UK: Cambridge University Press. ISBN 9780521154215.Schmidt-Rohr, K. (2015). "Why Combustions Are Always Exothermic, Yielding About 418 kJ per Mole of O2". J. Chem. Educ. 92 (12): 2094–99. doi:10.1021/acs.jchemed.5b00333Ward, Michael (March 2005). Fire Officer: Principles and Practice. Jones & Bartlett Learning. ISBN 9780763722470. Cite this Article Format mla apa chicago Your Citation Helmenstine, Anne Marie, Ph.D. "What Is Fire Made Of?" ThoughtCo, Jun. 4, 2022, thoughtco.com/what-is-fire-made-of-607313. Helmenstine, Anne Marie, Ph.D. (2022, June 4). What Is Fire Made Of? Retrieved from https://www.thoughtco.com/what-is-fire-made-of-607313 Helmenstine, Anne Marie, Ph.D. "What Is Fire Made Of?" ThoughtCo. https://www.thoughtco.com/what-is-fire-made-of-607313 (accessed June 9, 2023). copy citation Featured Video