8 Science Chapter 5 Coal And Petroleum

Chapter Notes and Summary
Resources : We have various materials for our basic needs. Some of them are found in nature and some have been made by human efforts.
Natural resources : various resources which are obtained from nature are called natural resources, e.g., air, water, soil, etc.
Natural resources are of two types as below :
Inexhaustible natural resources : These resources are present in unlimited quantity in nature, e.g., sunlight, air.
Exhaustible natural resources : amount of these resources in nature is limited. They can be exhausted by human activities, e.g., forest, wildlife, petroleum gas, etc.
Fuels : Substances that burn in air to give heat and energy are called fuels.
Fossil Fuels : Some exhausted natural resources like fuel were formed from dead plants and animals of living organisms. These are also known as fossil fuels.
Coal : It is fossil fuel. It is formed by anaerobic thermal degradation of dead plants and animals, which got buried inside earth over millions of years. Since, it was formed from remains of plants and animals, so it is called fossil fuel.
• Coal is one of fuels used to cook food. It is used in railway engines to produce steam to run engine. It is also used in thermal power plants to produce electricity. Coal is also used as a source of many organic compounds such as benzene, toluene, phenol, etc.
Destructive Distillation of Coal : process of heating wood or coal in absence of air is called destructive distillation. When coal is heated strongly in absence of air in closed retorts, various useful products are obtained.
Products obtained from coal :
Coke : It is a tough, porous and black substance obtained from coal. It is almost a pure form of carbon.
Uses :
Coke is used as a reducing agent in extraction of metals such as iron, zinc etc. It is used in manufacture of steel. It is used as a fuel.
Coal gas : It is a gas obtained during processing of coal to get coke. It can be used as a source of light and heat.
Uses :
It is a gaseous fuel obtained during processing of coal to get coke.
Coal tar : It is black, thick liquid obtained as product, during processing of coal to get coke. It is a mixture of 200 substances. Many of its products are used as starting materials for manufacture large number of substances such as dyes, drugs, perfumes, naphthalene balls.
Uses :
Coal tar was also used for metalling roads. Now-a-days, a petroleum, bitumen is used for metalling roads.
Natural gas : It is a very important fossil fuel. Natural gas is stored under high pressure as compressed natural gas
(Cna). CNG is very less polluting and cheaper fuel.
Petroleum : It is a dark oily liquid from which many valuable substances, like petrol and diesel are obtained. It is found deep below earth’s crust trapped in rocks in certain areas. It is also called crude oil or mineral oil.
Formation of petroleum : Petroleum was formed from remains of plants and animals buried under sea by decomposition, millions of years ago. plants and animals which lived in sea, died and their bodies settled at bottom of sea and got covered with mud, sand and clay. Due to high temperature and pressure, and absence of air, these were slowly converted into petroleum and natural gas. Petroleum is extracted by drilling holes (oil wells) in earth’s crust. In drilling, Natural gas comes out fist with great pressure and then crude petroleum comes out.
Refining of petroleum : process of separating constituents or fractions of petroleum is called refining.
Various constituents of petroleum and their uses :
S.No. Constituents of petroleum Uses
1.
Petroleum gas in liquid form (LPG) Fuel for home and industries
2.
Petrol Motor fuel, aviation fuel, solvent for dry cleaning
3.
Kerosene Fuel for stoves, lamps and for jet aircrafts
4.
Diesel Fuel for heavy motor vehicles, electric generators
5.
Lubricating oil Lubrication
6.
Paraffin wax Ointments, candles, vaseline, etc.
7.
Bitumen Paints, road surfacing
Natural resources are limited : Coal and petroleum are fossil fuels. It required dead organism million of years to get converted into their fuels. known reserves will last only a few hundred years. Burning of fuels is a major cause of air pollution. Their use is also linked to global warming. It is therefore necessary that we use these fuels only when absolutely necessary. In India, PCRA (Petroleum Conservation Research Association) advises how to save petrol/diesel, their tips are as below :
• Drive at a constant and moderate speed as far as possible.
• Switch off engine at traffic lights or at a place where you have to wait.

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