Thus, the produced smoke is usually toxic and contains unburned or partially oxidized products. However, complete combustion is almost impossible to achieve, since the chemical equilibrium is not necessarily reached, or may contain unburnt products such as carbon monoxide, hydrogen and even carbon ( soot or ash). Thermodynamically, the chemical equilibrium of combustion in air is overwhelmingly on the side of the products. Complete combustion is stoichiometric concerning the fuel, where there is no remaining fuel, and ideally, no residual oxidant. Uncatalyzed combustion in air requires relatively high temperatures. This reaction releases 242 kJ/ mol of heat and reduces the enthalpy accordingly (at constant temperature and pressure):Ģ H 2 ( g ) + O 2 ( g ) → 2 H 2 O ↑ A simple example can be seen in the combustion of hydrogen and oxygen into water vapor, a reaction which is commonly used to fuel rocket engines. Combustion is often hot enough that incandescent light in the form of either glowing or a flame is produced.
Solid fuels, such as wood and coal, first undergo endothermic pyrolysis to produce gaseous fuels whose combustion then supplies the heat required to produce more of them. While the activation energy must be overcome to initiate combustion (e.g., using a lit match to light a fire), the heat from a flame may provide enough energy to make the reaction self-sustaining.Ĭombustion is often a complicated sequence of elementary radical reactions. Combustion does not always result in fire, because a flame is only visible when substances undergoing combustion vaporize, but when it does, a flame is a characteristic indicator of the reaction. Air pollution abatement equipment provides combustion control for industrial processes.Ĭombustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke.
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