Class 8 NCERT Solutions Science Chapter 3 - Coal and Petroleum
Coal and Petroleum Exercise 38
The advantages of using compressed natural gas (CNG) and liquified petroleum gas (LPG) as fuels are:
(i) They can be burnt directly.
(ii) They can be transported easily through pipe lines.
(iii) They are clean fuels and do not give smoke when burnt.
(iv) They have high calorific value.
Concept insight: gaseous fuels are considered best fuels as they are economical and create less pollution.
Bitumen, a petroleum product, is used for surfacing roads.
Millions of years ago, dense forests got buried under the soil due to natural processes like storms, floods, and earthquakes. These got compressed as more and more soil got deposited over them. When they got buried deep in the soil, they were exposed to very high pressure and temperature. Under these conditions, these slowly got converted into coal. This process of formation of coal from dead vegetation is called carbonization.
(a) Fossil fuels are coal, petroleum and natural gas.
(b) Process of separation of different constituents from petroleum is called __refining__.
(c) Least polluting fuel for vehicles is __compressed natural gas (CNG)__.
(a) Fossil fuels can be made in the laboratory. False
Concept insight: coal and petroleum are formed from dead plants and animals buried in the earth which were decomposed under immense pressure and heat.
(b) CNG is more polluting fuel than petrol. False
Concept insight: CNG is a gaseous fuel so is a better and less polluting fuel than petrol.
(c) Coke is almost pure form of carbon. True
(d) Coal tar is a mixture of various substances. True
(e) Kerosene is not a fossil fuel. False
Concept insight: Kerosene is obtained by fractional distillation of petroleum so it is a fossil fuel.
Fossil fuels require millions of years to form from the dead vegetation and animals that get buried deep inside the Earth. They require high temperature and pressure for their formation, which cannot be provided in the laboratory and their rate formation is very less in comparison to their rate of consumption so they will exhaust in near future due to current rate of consumption.
Coal and Petroleum Exercise 39
Characteristics of coke are:
(iii) Black in colour
Uses of coke:
(i) In manufacture of steel.
(ii) In the extraction of metals (as a reducing agent).
Petroleum was formed from dead organisms that got buried in the sea millions of years ago. These dead bodies got covered with layers of sand and clay. Lack of air, high temperature, and high pressure transformed these dead organisms into petroleum and natural gas.