Page 57 - Chemistry ICSE Class IX

Chemical Changes and Reactions 45
Combustion

What is combustion
Combustion is a chemical process. It is de ned as follows:
# EJGOKECN TGCEVKQP KP YJKEJ JGCV CPF NKIJV KP VJG HQTO QH C ƀCOG
are given out is called combustion.

Combustion may also be de ned as follows:
Burning is an example of
Combustion is a rapid oxidation/burning of any substance in which
heat and light are produced. combustion because during
burning, heat and light are given
Burning/combustion of a combustible substance in presence of excess out
of the supporter of combustion is called complete combustion. Complete
combustion is generally called simply as combustion.
ŽŵďƵƐƟŽŶ ŝƐ ĂŶ ĞdžŽƚŚĞƌŵŝĐ
Combustion of some common substances are described below: ƉƌŽĐĞƐƐ ďĞĐĂƵƐĞ ŚĞĂƚ ŝƐ ŐŝǀĞŶ ŽƵƚ
ƒ Combustion of carbon. Carbon (or charcoal) burns in air or oxygen to ĚƵƌŝŶŐ ĐŽŵďƵƐƟŽŶ͘
give CO producing heat and light.
2
combustion
C(s) + O (g) o CO (g) + Heat + Light
2
2
carbon oxygen carbon dioxide
(or charcoal) (from air)
ƒ Combustion of hydrocarbons. Hydrocarbons burn to produce carbon
dioxide (CO ), water (H O), heat and light. For example, burning of
2
2
methane is described by the following equation:
combustion
CH (g) + 2O (g) o CO (g) + 2H O(g) + Heat + Light
2
2
4
2
methane from air
Naphthalene (moth balls),
Natural gas and biogas contain methane. So, burning of natural gas camphor, etc. burn with a sooty
and biogas are also combustion reactions. flame
Burning of LPG (which contains mainly butane) produces CO , H O,
2
2
heat and light. tŚĞŶ ŽƌĚŝŶĂƌLJ ĐŽĂů͕ ǁŽŽĚ Žƌ ĂŶLJ
combustion
C H (g) + 13 O (g) o 4CO (g) + 5H O(g) + Heat + Light ƉĞƚƌŽůĞƵŵͲďĂƐĞĚ ĨƵĞů ŝƐ ďƵƌŶƚ͕ ƚŚĞŶ
2
10
2
2
4
2
butane/LPG ƵƐƵĂů ƉƌŽĚƵĐƚƐ ŽĨ ĐŽŵďƵƐƟŽŶ ĂƌĞ
ĐĂƌďŽŶ ĚŝŽdžŝĚĞ ; K Ϳ ĂŶĚ ǁĂƚĞƌ
ƒ Combustion of cellulose. Wood, paper, cotton cloth, etc., all contain ;, KͿ͘ ƵƌŶŝŶŐ ŽĨ ĐĂƌďŽŶ Žƌ ĐŚĂƌĐŽĂů
Ϯ
Ϯ
cellulose. Cellulose is a carbohydrate and can be described by the ŵĂŝŶůLJ ƉƌŽĚƵĐĞƐ K ͘
Ϯ
formula (C H O ) . On combustion, cellulose (like wood, cotton cloth
5 n
6
10
and paper) gives CO and H O as follows:
2
2
(C H O ) (s) + 6nO (g) o 6nCO (g) + 5nH O(g) + Heat + Light
2
6
2
2
10
5 n
cellulose
ƒ Combustion of alcohol. Alcohols, such as ethanol, burn to give a
ame and heat.
burn
C H OH(l) + 3O (g) o 2CO (g) + 3H O(g) + Heat + Light
2
2
2
2
5
ethanol oxygen (in air) carbon dioxide water
What are combustible and noncombustible substances
All substances may be classi ed as combustible or noncombustible.
ƒ The substances which burn readily are called combustible
substances. For example, petrol, LPG (cooking gas), wax, kerosene, /ƚ ŵĂLJ ďĞ ŶŽƚĞĚ ŚĞƌĞ ƚŚĂƚ Ă
paper, cloth, wood, coal, etc. are combustible substances. ƐƵƉƉŽƌƚĞƌ ŽĨ ĐŽŵďƵƐƟŽŶ ŝƚƐĞůĨ ŝƐ
ŶŽƚ Ă ĐŽŵďƵƐƟďůĞ ŵĂƚĞƌŝĂů͕ ďƵƚ ŝƚ
ƒ The substances which do not burn are called noncombustible ŽŶůLJ ŚĞůƉƐ ŝŶ ƚŚĞ ĐŽŵďƵƐƟŽŶ ŽĨ ĂŶLJ
substances. For example, water, glass, sand, etc. are noncombustible ĐŽŵďƵƐƟďůĞ ƐƵďƐƚĂŶĐĞ͘
substances.