Page 109 - ICSE Chemistry 6

heat. Burning of coal also gives off carbon dioxide and water vapour along with ash and smoke. Hence, burning
of coal results in air pollu on.

LPG
LPG stands for Liquefi ed Petroleum Gas. It is the same gas which is used in houses for cooking food. As the
name suggests, this gas is stored in liquid state under pressure in cylinders. LPG on burning also gives out
carbon dioxide, water vapour and heat energy.
CNG

Another example of naturally occurring gaseous form of fuel is CNG or the Compressed Natural Gas. Like
LPG, it is also compressed and stored in cylinders. CNG is mainly used as a fuel to run vehicles like buses,
autorickshaws and cars. It produces heat energy on burning and does not pollute air. Hence, it is a clean fuel
and is cheaper than petrol and diesel.

Petrol, Diesel and Kerosene
Petrol, diesel and kerosene are important fossil fuels obtained from crude petroleum. They release heat energy
but cause air pollu on on burning.

The burning of fossil fuels such as oil, natural gas and coal releases carbon dioxide into the atmosphere.
The concentra on of carbon dioxide has increased over the past century due to huge consump on of
fossil fuels worldwide. This con nued increase in carbon dioxide concentra on could result in major
changes in global climate.

Similarities between Respiration and Combustion
• Oxygen is required in both the processes: respira on and combus on.

• The forma on of carbon dioxide and water vapour occurs in both the processes.

Differences between Respiration and Combustion

Respiration Combustion

• It is an artiϐicial process and is performed when
• It is a natural and continuous process
required.
• It is a slow process. • It is a fast process.
• It releases a small amount of energy in the form of • It releases a large amount of energy in the form of
heat. heat and light.
• It occurs at a higher temperatures and requires
• It occurs at body temperature.
initiation.

MAINTENANCE OF AIR COMPOSITION IN NATURE

We have learnt that plants and animals need oxygen for respira on and give out carbon dioxide and water
vapour. The other process which requires oxygen is burning. In this process also, carbon dioxide and water
vapour are given out as by-products. If both the processes con nue to operate in nature, the percentage
of oxygen, carbon dioxide and water vapour in the air will change appreciably and this will result in an
imbalance in nature. Hence, to maintain a balance between these gases, several other processes operate

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