NCERT 8th Class (CBSE) Science: Coal and Petroleum

Question: Why are fossil fuels our most important source of energy today?

Answer: Fossil fuels have been in use since a long time and called conventional sources of energy. On burning it gives us heat and light. The deposits of fossil fuels are going to be exhausted in less than 200 years and took millions of years to form. This is why fossil fuels are the most import sources of energy today. we must conserve fuels as much as possible so that the existing deposits could last longer and scientists can develop alternate fuels.

Question: What is the main purpose of petroleum refining?

Answer: Petroleum contains various hydrocarbons which can be used for different purposes. Therefore, Refining of petroleum is carried out to get Constituents of petroleum like LPG, Petrol, kerosene, diesel etc.

Question: If a resource is renewable, it can still get exhausted. Discuss with two examples.

Answer: If we use renewable resources faster than they are renewed or if we disturb the natural method of their renewal, then most renewable resources get exhausted. For example:

1. Groundwater is used faster than it is renewed.
2. Forest is a renewable resource provided we don’t disturb their natural growth.

Question: Why is topsoil considered a non-renewable resource even though it is constantly being formed by weathering of rocks?

Answer: Topsoil considered a non-renewable resource even though it is constantly being formed by weathering of rocks because it takes hundreds of years to form. Once topsoil is eroded, it cannot be replaced immediately.

Question: Why do we feel the need for conservation more today than our ancestors did?

Answer: We feel the need for conservation more today than our ancestors did. There are two primary reasons for this:

1. The population of the world has increased. There are more people on the earth, and they use more resources to feed, clothe and house themselves.
2. As human have progressed, their need have increased. Their need for energy has increased several folds. The average resources consumed per person have, therefore, increased considerably.

Because of these two factors, the natural resources today are getting used up and depleted much faster than a few decades back. Therefore, if we do not practice conservation, we will endanger our very survival.

Question: How was coal formed?

Answer: Coal is formed over a period of million of years, by the gradual decay and compression of buried remains of ancient forests. The high temperature and high pressure inside the earth slowly converted the buried vegetation into coal. As coal contains mainly carbon, this slow process of conversion of wood into coal is called carbonization.