| Combustion |
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Burning of a substance is called combustion. Substances that burn in air or oxygen easily or catch fire easily are called combustible substances. Example: Coal, hydrogen, wood, hydrocarbons, sulphur, phosphorous, sodium, potassium, calcium, magnesium, etc. The substances, which do not burn in air or oxygen even on strong heating, are called non-combustible substances. Stones, sand and common salt are solid non-combustible substances; water is non-combustible liquid; nitrogen, sulphur dioxide and carbon dioxide are non-combustible gases. The combustible substances, which combine with oxygen of air at comparatively low temperature, to produce large amount of heat and light, accompanied by a flame, are called inflammable substances. Liquids and gases are generally inflammable in nature. Petrol, kerosene oil, ether and alcohol are inflammable liquids. L.P.G., methane, hydrogen and carbon monoxide are inflammable gases.
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A substance in the presence of which combustion occurs is said to be a supporter of combustion. Air is the main supporter of combustion on earth. It is the oxygen in air, which supports combustion. Nitrogen oxide (Nitrous oxide) is another gas, which supports combustion like oxygen. The gaseous environment determines the rate of combustion. Substances burn more rapidly in pure oxygen than in air, because of higher concentration of oxygen.
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The minimum temperature, to which a substance must be raised, before it can combine with oxygen of air, is called ignition temperature. Ex: Ether, carbon disulphide and petrol have ignition temperature less than 500C. |
| Size of particle of a combustible substance determines its rate of combustion. Smaller is the size of particle, faster is the rate of combustion. Ex: Coal dust catches fire more rapidly as compared to solid coal. Inflammable substances burn rapidly as compared to substances like wood or coal. Ex: Petrol catches fire more rapidly as compared to wood. |
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