What is a fire chemically ?
Answer:
FIRE CHEMISTRY :
Broadly speaking there are two types of fire, flaming and smoldering fires, and they exhibit traits unique to themselves.
Flaming:
Flaming fires involve the rapid oxidation of a fuel (combustion or release of energy) with associated flame, heat, and light. The flame itself occurs within a region of gas where intense exothermic reactions are taking place. An exothermic reaction is a chemical reaction that takes place within a substance whereby heat and energy are released as the substance changes to a simpler chemical form. As chemical reactions occur within the fuel being burned, light is usually emitted as photons are released by the oxidation of the fuel. Depending upon the specific chemical and physical change taking place within the fuel the flame may or may not emit light. For example, burning alcohol is usually invisible although the heat given off is tremendous. The visible flame has no mass. What we see as visible flame is actually energy (photons) being released in the form of light by the oxidation of the fuel. The color of the flame is dependent upon the energy level of the photons emitted. Lower energy levels produce colors toward the red end of the light spectrum while higher energy levels produce colors toward the blue end of the spectrum. The hottest flames are white in appearance. The color of a fire may also be affected by chemical elements in the flame, such a barium giving a green flame color.
Smouldering :
The latter example, a smoldering fire, is a flameless form of combustion, deriving its heat from oxidations occurring on the surface of a solid fuel. Two common examples are glowing coals and cigarettes. Smolder propagates in a creeping fashion over solid fuels or inside porous fuels, and its temperature and heat released are low in comparison. The difference between flaming and smoldering combustion is that the latter occurs on the surface of the solid rather than in the gas phase.
Chemical Reactions :
Fires start when both a flammable and/or a combustible material with an adequate supply of oxygen or another oxidizer is subjected to enough heat. This is commonly called the fire triangle. No fire can exist without all three elements being in place.
The common fire-causing sources of heat include:
-sparks
-another fire (such as an explosion)
-a fire in the oven or fireplace
-a lit match, lighter or cigarette
-sources of intense thermal radiation (such as sunlight or an incandescent light bulb)
Joule heating, friction or exhaust gas from mechanical or electrical machinery
Once ignited, fires can sustain their own heat by the further release of heat energy in the process of combustion and may propagate, provided there is a continuous supply of oxygen and fuel.
Fire can be extinguished by removing any one of the elements of the fire triangle. The traditional extinguishant of water acts by cooling the combusting material to stop the reaction, whereas a Carbon Dioxide extinguisher acts by starving the fire of oxygen.
The unburnable solid remains of a combustible material left after a fire are called ash, soot or cinder.
Flame :
A flame is an exothermic, self-sustaining, oxidizing chemical reaction producing energy and glowing hot matter, 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 depends on the chemical composition of the burning elements and intermediate reaction products.
In many cases, such as the burning of organic matter, for example wood, or the incomplete combustion of gas, incandescent solid particles called soot produce the familiar red-orange glow of 'fire'. This light has a continuous spectrum. Complete combustion of gas has a dim blue color due to the emission of single-wavelength radiation from various electron transitions in the excited molecules formed in the flame. For reasons currently unknown by scientists, the flame produced by exposure of zinc to air is a bright green, and produces plumes of zinc oxide. Usually oxygen is involved, but hydrogen burning in chlorine also produces a flame, producing hydrogen chloride (HCl). Other possible combinations producing flames, amongst many more, are fluorine and hydrogen, and hydrazine and nitrogen tetroxide.
The glow of a flame is 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 on 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, the fire is white, the hottest color possible for organic material in general, or yellow. Above the yellow region, the color changes to orange, which is 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.
The National Aeronautics and Space Administration (NASA) of the United States has recently found that gravity plays a role. Modifying the gravity causes different flame types. 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, 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 it 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 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 behave differently in microgravity when compared to normal gravity conditions. These discoveries have potential applications in applied science and industry, especially concerning fuel efficiency.
In combustion engines, various steps are taken to eliminate a flame. The method depends mainly on whether the fuel is oil, wood, or a high-energy fuel such as jet fuel.
The release of energy
a rapid oxidation process that releases heat, light and smoke, and energy in varying intensities
Fire is a rapid oxidation process that creates light, heat, smoke, and releases energy in varying intensities. 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 how to make fire is considered one of humankind's most important advances, allowing higher hominids to ward off wild animals, cook food, and control their own source of light and warmth.
Chemistry
Broadly speaking there are two types of fire, flaming and smoldering fires, and they exhibit traits unique to themselves.
Flaming
Flaming fires involve the rapid oxidation of a fuel (combustion or release of energy) with associated flame, heat, and light. The flame itself occurs within a region of gas where intense exothermic reactions are taking place. An exothermic reaction is a chemical reaction that takes place within a substance whereby heat and energy are released as the substance changes to a simpler chemical form. As chemical reactions occur within the fuel being burned, light is usually emitted as photons are released by the oxidation of the fuel. Depending upon the specific chemical and physical change taking place within the fuel the flame may or may not emit light. For example, burning alcohol is usually invisible although the heat given off is tremendous. The visible flame has no mass. What we see as visible flame is actually energy (photons) being released in the form of light by the oxidation of the fuel. The color of the flame is dependent upon the energy level of the photons emitted. Lower energy levels produce colors toward the red end of the light spectrum while higher energy levels produce colors toward the blue end of the spectrum. The hottest flames are white in appearance. The color of a fire may also be affected by chemical elements in the flame, such a barium giving a green flame color.
Smouldering
The latter example, a smoldering fire, is a flameless form of combustion, deriving its heat from oxidations occurring on the surface of a solid fuel. Two common examples are glowing coals and cigarettes. Smolder propagates in a creeping fashion over solid fuels or inside porous fuels, and its temperature and heat released are low in comparison. The difference between flaming and smoldering combustion is that the latter occurs on the surface of the solid rather than in the gas phase.
Chemical Reaction
The fire triangleFires start when both a flammable and/or a combustible material with an adequate supply of oxygen or another oxidizer is subjected to enough heat. This is commonly called the fire triangle. No fire can exist without all three elements being in place.
The common fire-causing sources of heat include:
sparks
another fire (such as an explosion)
a fire in the oven or fireplace
a lit match, lighter or cigarette
sources of intense thermal radiation (such as sunlight or an incandescent light bulb)
Joule heating, friction or exhaust gas from mechanical or electrical machinery
Once ignited, fires can sustain their own heat by the further release of heat energy in the process of combustion and may propagate, provided there is a continuous supply of oxygen and fuel.
Fire can be extinguished by removing any one of the elements of the fire triangle. The traditional extinguishant of water acts by cooling the combusting material to stop the reaction, whereas a Carbon Dioxide extinguisher acts by starving the fire of oxygen.
The unburnable solid remains of a combustible material left after a fire are called ash, soot or cinder.
Flame
A flame is an exothermic, self-sustaining, oxidizing chemical reaction producing energy and glowing hot matter, 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 depends on the chemical composition of the burning elements and intermediate reaction products.
In many cases, such as the burning of organic matter, for example wood, or the incomplete combustion of gas, incandescent solid particles called soot produce the familiar red-orange glow of 'fire'. This light has a continuous spectrum. Complete combustion of gas has a dim blue color due to the emission of single-wavelength radiation from various electron transitions in the excited molecules formed in the flame. For reasons currently unknown by scientists, the flame produced by exposure of zinc to air is a bright green, and produces plumes of zinc oxide. Usually oxygen is involved, but hydrogen burning in chlorine also produces a flame, producing hydrogen chloride (HCl). Other possible combinations producing flames, amongst many more, are fluorine and hydrogen, and hydrazine and nitrogen tetroxide.
The glow of a flame is 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 on 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, the fire is white, the hottest color possible for organic material in general, or yellow. Above the yellow region, the color changes to orange, which is 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.
Fire is a rapid oxidation process that creates light, heat, smoke, and releases energy in varying intensities...
flames are the movement of electron from their excited stated back to their oringal state. when it does that it releaces engery. in the form of light and heat.
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