Page 59 - Chemistry ICSE Class IX
P. 59
Chemical Changes and Reactions 47
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If the ignition temperature of any substance is lower than the room
temperature, it will catch re as soon as it is brought into the air. In
such a case, no initial heating is needed. Such substances are called
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For example, yellow phosphorus having ignition temperature of 30°C
catches re when kept in air. It is due to this reason that yellow phosphorus
is always stored under water.
What is incomplete (or partial) combustion
Burning of a combustible substance in the presence of a limited amount of
the supporter of combustion, is commonly called incomplete combustion
or partial combustion. For example, when carbon is burnt in the presence
of limited amount of oxygen (or air), it is called incomplete combustion.
Carbon during incomplete combustion, produces carbon monoxide (CO).
Complete combustion: C(s) + O (g) o CO (g) + Heat + Light
2
2
carbon (excess) carbon dioxide
Incomplete combustion: 2C(s) + O (g) o 2CO(g) + Heat + Light
2
carbon (limited)
Thus, when any carbon-containing combustible substance undergoes
combustion in the presence of limited air (or oxygen), it undergoes partial
combustion producing CO, CO and unburnt carbon particles.
2
What are the disadvantages of incomplete combustion
Following are the disadvantages or harmful effects of incomplete
combustion:
During incomplete combustion, both carbon monoxide (CO) and
carbon dioxide (CO ) are produced. Carbon monoxide is a highly
2
poisonous pollutant. If inhaled, it can cause death.
During incomplete combustion, the heat produced is less than that
produced during complete combustion. So, incomplete combustion
leads to higher consumption of fuel (combustible material).
Sometimes, incomplete combustion leads to the formation of unburnt
carbon particles. These WPDWTPV ECTDQP RCTVKENGU OCMG VJG ƀCOG
sooty or smoky.
Why is respiration called a slow combustion
We have seen that during respiration, the carbon-containing compounds
react with oxygen to form CO and H O, and energy is released. CO , H O
2
2
2
2
and energy are also the products of combustion. This shows that respiration
is similar to combustion. But, respiration takes place slowly at body
temperature. Therefore, respiration is called slow combustion. Respiration
is also called spontaneous combustion.
How does combustion differ from respiration
Respiration is similar to combustion, but still there are many differences
between the two. Some differences between the two are described in
Table 2.2.
