What Is Fire Made Of?

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?

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. Flames consist primarily of carbon dioxide, water vapor, oxygen, and nitrogen.

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.

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.

On Fire, Adobe Flash-based science tutorial from the NOVA television series.