Thursday, 18 April 2013

ch5 sci class8

Question 1. What are the advantages of using CNG and LPG as fuels?
Answer : CNG -  compressed natural gas, is stored under high pressure as compressed natural gas (CNG).  CNG is a very important fossil fuel because it is easy to transport through pipes. CNG is used for power generation. It is now being used as a fuel for transport vehicles because it is less polluting. It is a cleaner fuel. Similarly, LPG- Liquified Petroleum Gas is used as fuel for home and industry as it is less polluting and easy to transport and to use.

Question 2. Name the petroleum product used for surfacing of roads.
Answer : Earlier coal-tar a black, thick liquid which is obtained from coal processing, and is   a mixture of about 200 substances was mainly used for metalling or surfacing of the roads, now a days, bitumen, which is a petroleum product, is used in place of coal-tar for metalling or surfacing of the roads.

Question 3. Describe how coal is formed from dead vegetation. What is this process called?

Answer : A long time back, about  300 million years ago the earth had dense forests in low lying wetland areas. Due to natural processes, like earth quakes, flooding, these forests got buried under the soil, rocks and other land masses. With the passage of time, as more soil deposited over them, they were compressed. The temperature also rose as they sank deeper and deeper. Under high pressure and high temperature, dead plants got slowly converted to coal. As coal contains mainly carbon, the slow process of conversion of dead vegetation into coal is called carbonisation. Since it was formed from the remains of vegetation, coal is also called a fossil fuel.

Question 4. Fill in the blanks :
(a) Fossil fuels are CoalPetroleum and Natural gas.
(b) Process of separation of different constituents from petroleum is calledRefining.
(c) Least polluting fuel for vehicle is  CNG (compressed natural gas) .

Question 5. Tick True/False against the following statements :
(a) Fossil fuels can be made in the laboratory. (F)
(b) CNG is more polluting fuel than petrol. (F)
(c) Coke is almost pure form of carbon. (T)
(d) Coal tar is a mixture of various substances. (T)
(e) Kerosene is not a fossil fuel. (F)

Question 6. Explain why fossil fuels are exhaustible natural resources.
Answer :The formation of fossil fuels is a very slow process, takes million of years in nature.We have limited  reserves of fossil fuels in nature . Fossil fuels are exhaustible natural resources, as limited fossil fuels reserves like  coal, petroleum, natural gas  are being depleted very fast by  human activities like rapid urbanization, industrialization  and transportation.

Question 7. Describe characteristics and uses of coke.
Answer : Coke is a tough, porous and black substance. It is almost pure form of carbon. Coke is used in the homes for cooking, heating and in industries, for manufacturing of steel and extraction of many metals.Earlier it was also used in steam engines for rail transporation.It is also used in thermal power plants to produce electricity.

Question 8. Explain the process of formation of petroleum.
Answer : Petroleum was formed from organisms living in the sea. As these organisms died, their bodies settled at the bottom of the sea and got covered with layers of sand and clay. Over millions of years, absence of air, high temperature and high pressure transformed the dead organisms into petroleum and natural gas.

Question 9. The following Table shows the total power shortage in India from 1991–1997. Show the data in the form of a graph. Plot shortage percentage for the years on the Y-axis and the year on the X-axis.
S. No.YearShortage (%)




Answer : 
Graph : Power Shortage ( %) in India from 1991-1997
CBSE Class VIII (8th) Science | Chapter 5. COAL  AND PETROLEUM | Lesson Exercises

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