NCERT Class VIII Science Solutions: Chapter 5-Coal and Petroleum Part 5

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Question 25:

Fill in the blanks and complete the story.

About 300 million years ago the earth had dense ________ in low lying wetland areas. Due to natural processes, like ______, these forests got buried under the ________. As more ________ deposited over them, they were compressed. The ________ also rose as they sank deeper and deeper. Under high ________ and high ________, dead plants got slowly converted into coal.

Answer:

About 300 million years ago the earth had dense forests in low lying wetland areas. Due to natural processes, like floods, these forests got buried under the soil. 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 into coal.

Question 26:

Match the items given in Column I with the items of Column II.

Match the Column I Column II. (Q)
Match the Column I Column II. (Q)

Column I

Column II

Used for road surfacing

Black gold

Natural gas

Vaseline and candles

Petroleum

Bitumen

Paraffin wax

CNG

Answer:

Match the Column I Column II. (A)
Match the Column I Column II. (A)

Column I

Column II

Used for road surfacing

iii Bitumen

Natural gas

iv CNG

Petroleum

i Black gold

Paraffin wax

ii Vaseline and candles

LONG ANSWER QUESTIONS

Question 27:

Name the products obtained and their uses when coal is processed in industry.

Answer:

  • Coal when processed in industry gives coke, coal tar and coal gas.

  • Coke is used in the manufacture of steel and in extraction of many metals.

  • Coal tar is used as starting material for manufacturing various sustances such as synthetic dyes, drugs, explosives, perfumes, paints etc.

  • Coal gas is used as fuel.

Question 28:

We say fossil fuels will last only for a few hundred years. Comment.

Answer:

Fossil fuels will last only for a few hundred years because they are exhaustible natural resources. If consumed at a rate faster than the rate at which these are formed in nature.

Once the present stock of these gets exhausted, no new supplies of these fossil fuels will be available to us in the near future because it required millions of years for the conversion of dead organisms into these fuels.

Question 29:

We read in newspapers that burning of fuels is a major cause of global warming. Explain why.

Answer:

Image of factors causing global warming

Factors Causing Global Warming

Image of factors causing global warming

Burning of fuels is a major cause of global warming because they produce a lot of greenhouse gas ‘Carbon dioxide’ on burning.

The earth’s atmosphere allows most of the sunlight that falls on it to pass through and heat the surface. But greenhouse gases such as carbon dioxide, methane, water vapours trap the heat radiated from earth. This leads to an increase in earth’s temperature.

This is known as greenhouse effect. When concentration of greenhouse gases such as carbon dioxide increases, greenhouse effect also increases. This is known as global warming. It may cause melting of ice caps and glaciers resulting the rise in sea levels.