Manual of Firemanship Book 1 Elements of combustion and extinction 1974 by Unknown

Author:Unknown
Format: epub

The text on this page is estimated to be only 26.23% accurate Chapter 6 Combustion oxygen or other oxidising agents. The following reactions are typical examples of combustion: fi) The oxygen may be supplied by the air. C + 02 = COa carbon dioxide 200 4" 02 = 2COg 2H2 + 02 = 2H.O (ii) The combustion may take place using oxygen which is contained within the burning material, the combustible material and the supporter of combustion being together m the same compound. 4CaHs (N03)3 = 12C0* + 1QH2Q 4- 6N2 + 02 nitro glycerine (iii) Oxygen may be provided by one of the materials in a mixture of compounds. The ‘thermite reaction* illustrates this principle: Fe2Oa 4^ 2A1 — — ► AlgOg Hh 2Fe 4- heat thermite mixture (iv) Elements other than oxygen may be considered as oxidising agents; examples of this are chlorine and fluorine* Thus combustion may occur with these substances. Hydrogen will burn explosively with chlorine: H2 + — ► 2HC1 Many organic (i.e, materials based on the chemistry of carbon) materials will burn readily in halogen gases: C10n1& + 8C12 — 16HC1 4- IOC turpentine Nitrogen is not usually thought of as an oxidising agent or even a reactive element* but some metals will burn vigorously in this gas. Magnesium, aluminium and their alloys form nitrides in combustion reactions : 3Mg + N2— +Mg3N2 magnesium nitride 2 Heat of reaction and calorific value All combustion reactions* such as those quoted above, involve giving out heat and are therefore called exothermic reactions. The quantity of heat produced per unit weight of fuel can be calculated, and is known as the calorific value of the fuel. For example, when 12 grams of carbon are burned to carbon dioxide 392 920 joules of 392 920 heat are produced* Thus* the calorific value for carbon is — yr — 32 813 joules per gram (J/g). 55

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