Fire

What is fire?

A. Fire is heat and light from rapid combination of oxygen and other materials. The flame, which gives the light, is composed of glowing particles of burning material and luminous gases. For fire to exist, a combustible substance must be present, the temperature must be high enough to cause combustion, and enough oxygen must be present to sustain rapid combustion.

Is fire matter?
A. Matter is anything that has mass and occupies space. The flame itself is a mixture of gases (vaporized fuel, oxygen, carbon dioxide, carbon monoxide, water vapor, and many other things) and so is matter. The light produced by the flame is energy, not matter. The heat produced is also energy, not matter.



Q. What is the State of Matter of Fire or Flame? Is it a Liquid, Solid, or Gas?

A. The ancient Greeks and alchemists thought that fire was an element. They also considered earth, air, and water to be elements. However, the modern definition of an element defines it by the number of protons a pure substance possesses. Fire is made up of many different substances, so it is not an element.
For the most part, fire is a mixture of hot gases. Flames are the result of a chemical reaction, primarily between oxygen in air and a fuel, such as wood or propane. In addition to other products, the reaction produces carbon dioxide, steam, light, and heat. If the flame is hot enough, the gases are ionized and become yet another state of matter: plasma.


Fire is burning, which is combustion, and combustion is a type of oxidation reaction. Oxidation means combined chemically with oxygen . Oxidation is an exothermic reaction, meaning it gives releases heat energy.
The chemical equations for the oxidation of carbon and hydrogen are:
C+O2 -->CO2 (This reaction occurs when there is enough oxygen for the formation of carbon dioxide.)
2C+O2--> (This reaction occurs when there is only enough oxygen for the formation of carbon monoxide.)
2H2 +O2--> 2H2O
These reactions release the energy you feel as heat and light.



Fire is a rapid oxidation process that creates light, heat, and smoke, and varies in intensity. It is commonly used to describe either a fuel in a state of combustion (e.g., a campfire, or a lit fireplace or stove) or a violent, destructive and uncontrolled burning (e.g., in buildings or a wildfire). The discovery of making fire is considered one of the most important evolutions of humankind, for it allowed higher hominids to ward off wild animals, cook food, and provide warmth as well as a source of light in darkness.

Fire can be considered to be a low temperature partial plasma. Plasma; an ionized gas, usually considered to be a distinct state of matter.
Flame
A flame is an exothermic, self-sustaining, oxidizing chemical reaction producing energy and glowing hot flame, of which a very small portion is plasma. It consists of reacting gases and solids emitting visible and infrared light, the frequency spectrum of which is dependent on the chemical composition of the burning elements and intermediate reaction products.
In many cases such as burning organic matter like wood or incomplete combustion of gas, incandescent solid particles, soot produces the familiar red-orange 'fire' color light. This light has a continuous spectrum. Complete combustion of gas has a dim blue color due to the emission of single wavelength radiations from various electron transitions in the excited molecules formed in the flame. Usually oxygen is involved, but hydrogen burning in chlorine produces a flame as well, producing the toxic acid hydrogen chloride (HCl). Other possible combinations producing flames, amongst many more, are fluorine and hydrogen, or hydrazine and nitrogen tetroxide. Recent discoveries by the National Aeronautics and Space Administration (NASA) of the United States also has found that gravity plays a role. Modifying the gravity causes different flame types.
The glow of a flame is somewhat complex. Black-body radiation is emitted from soot, gas, and fuel particles, though the soot particles are too small to behave like perfect blackbodies. There is also photon emission by de-excited atoms and molecules in the gases. Much of the radiation is emitted in the visible and infrared bands. The color depends on temperature for the black-body radiation, and chemical makeup for the emission spectra. The dominant color in a flame changes with temperature. The photo of the forest fire is an excellent example of this variation. Near the ground, where most burning is occurring, it is white, the hottest color possible for organic material in general, or yellow. Above the yellow region, the color changes to orange, which is somewhat cooler, then red, which is cooler still. Above the red region, combustion no longer occurs, and the uncombusted carbon particles are visible as black smoke. To eliminate a flame in combustion vehicles there are different steps that are taken. This depends largely on whether the fuel is oil, wood, or high energy (such as fuel for jet engines).
The common distribution of a flame under normal gravity conditions depends on convection, as soot tends to rise to the top of a general flame, such as in a candle in normal gravity conditions, making it yellow. In microgravity or zero gravity, such as an environment in outer space, convection no longer occurs, and the flame becomes spherical, with a tendency to become more blue and more efficient (although they will go out if not moved steadily as the CO2 from combustion does not disperse in microgravity, and tends to smother the flame). There are several possible explanations for this difference, of which the most likely is that the temperature is evenly distributed enough that soot is not formed and complete combustion occurs. Experiments by NASA in microgravity reveal that diffusion flames in microgravity allow more soot to be completely oxidized after they are produced than diffusion flames on Earth, because of a series of mechanisms that behaved differently in microgravity when compared to normal gravity conditions.These discoveries have potential applications in applied science and industry, especially concerning fuel efficiency.

Typical temperatures of fires and flames
• Oxyhydrogen Flame (2000 °C or above)(3645 °F)
• Bunsen Burner Flame (min. to max. setting) (1300 to 1600 °C)(2372-2912 °F)

• Blowtorch Flame (1800 °C)(2370 °F)
• Candle Flame (760 °C)(1400 °F)
• Smouldering cigarette:
o Temperature without drawing: Side of the lit portion; 400 °C (or 750 °F);
Middle of the lit portion: 585 °C (or 1110 °F)
o Temperature during drawing: Middle of the lit portion: 700 °C (or 1290 °F)
• Always hotter in the middle.
Reference:
Illinois Institute of Technology 3300 South Federal Street, Chicago, Dr. Anne Marie Helmenstine.