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Spontaneous combustion is a type of combustion that occurs by self-heating (increase in temperature due to exothermic internal reactions), followed by thermal runaway (self-heating which rapidly accelerates to high temperatures) and finally, ignition. For example, phosphorus self-ignites at room temperature without the application of heat.
The combustion of a stoichiometric mixture of fuel and oxidizer (e.g. two moles of hydrogen and one mole of oxygen) in a steel container at 25 °C (77 °F) is initiated by an ignition device and the reactions allowed to complete. When hydrogen and oxygen react during combustion, water vapor is produced.
As an example in everyday life, hand warmers make use of the oxidation of iron to achieve an exothermic reaction: 4Fe + 3O 2 → 2Fe 2 O 3 Δ H ⚬ = - 1648 kJ/mol A particularly important class of exothermic reactions is combustion of a hydrocarbon fuel, e.g. the burning of natural gas:
According to the IUPAC, an exothermic reaction is "a reaction for which the overall standard enthalpy change ΔH⚬ is negative". [4] Some examples of exothermic process are fuel combustion, condensation and nuclear fission, [5] which is used in nuclear power plants to release large amounts of energy. [6]
A large compost pile can spontaneously combust if not properly managed. Spontaneous combustion or spontaneous ignition is a type of combustion which occurs by self-heating (increase in temperature due to exothermic internal reactions), followed by thermal runaway (self heating which rapidly accelerates to high temperatures) and finally, autoignition. [1]
Incomplete reaction at higher temperature further curtails the effect of a larger heat of combustion. [citation needed] Because most combustion processes that happen naturally occur in the open air, there is nothing that confines the gas to a particular volume like the cylinder in an engine.
Typical examples of exothermic reactions are combustion, precipitation and crystallization, in which ordered solids are formed from disordered gaseous or liquid phases. In contrast, in endothermic reactions, heat is consumed from the environment.
Smouldering combustion in glowing embers of barbecue coal briquettes. Smouldering (British English) or smoldering (American English; see spelling differences) is the slow, flameless form of combustion, sustained by the heat evolved when oxygen directly attacks the surface of a condensed-phase fuel. [1]