Coal and Petroleum CBSE Class 8 Science Revision Notes Chapter 5

Figure 1 Classification of Resources

Coal, Petroleum and Natural Gas are exhaustible natural resources. They are fossil fuels.

Fossil fuels are fuels that are formed by fossils (or dead remains) of living organisms.

What are fuels?

A fuel is any substance that releases large amounts of energy in the form of heat and light when it is burned. For example, coal and petroleum are fuels.

Fuels can be classified as:

Why do we need fossil fuels?

Fuels are required for different purposes such as:

1. Transportation: fuels are used to run different vehicles such as cars, trucks, motorcycles, trains, airplanes etc.

2. Cooking: fuels are needed for cooking. For instance, LPG is used in urban areas while firewood, coal and cattle dung is used in rural areas.

3. Heating: fuel is also used to generate heat

4. Electricity production: different fuels such as coal, petrol, natural gas and diesel are used to generate electricity in power plants

5. Industrial usage: many industries use fuels for different purposes such as producing electricity, running their machinery and heating

6. Rockets and other space vehicles: fuels called propellants are used in rockets that help in launching the space vehicles

What are the characteristics of a good fuel?

The characteristics of good fuel are:

1. It should be economical.

2. It should be available easily

3. It should not emit poisonous gases on burning

4. It should produce large amounts of heat with respect to its mass (it should have a high calorific value)

5. It should be easy to transport and handle

6. It should not produce a bad odour

7. It should be clean and should not produce many ashes

8. It should not ignite easily at room temperature

Coal

Figure 2 Coal

Coal is a fossil fuel formed from dead plant matter over millions of years due to heat and pressure.

How is Coal formed?

Figure 3 Formation of Coal

• Over millions of years, coal is formed through different biological and geological processes on dead and decaying plant matter.

• Coal mainly contains carbon. The process of conversion of dead vegetation into coal is called carbonisation.

• Coal comes from a coal mine.

• What is the composition of coal?

  • Coal consists of hydrogen, carbon and oxygen and sulphur (small amount).

• What is coal mining?

  • Coal is extracted from the ground with a process called mining. Coal Mining can be of two types:

1. Opencast Mining: Mining in which coal is extracted from near the earth’s surface

2. Underground Mining: Mining in which coal is extracted from deep inside the earth’s crust

Different Types Coal

As coal gets older, the carbon content in it is higher. When coal is burnt, it mainly produces carbon dioxide gas.

Figure 4 Types of Coal

Uses of Coal

• Used as fuel to cook food.

• Used in thermal power plants to produce electricity.

• Used as fuel in various industries.

• Once used as fuel to run steam-powered railway engines.

When processed, coal yields coke, coal tar and coal gas which in turn is used by many industries.

What is destructive distillation?

Figure 5 Destructive Distillation

It is a process in which coal is heated at very high temperature in the absence of air to obtain various useful products from it. Consider the diagram below to understand the process of destructive distillation. Different products obtained through this process are coal gas, coal tar, coke and liquor ammonia.

Figure 6 Destructive Distillation Process Flow Chart

Major Coal Products

Figure 7 Coal products

What are hydrocarbons?

Hydrocarbons are the substances that consist of only carbon and hydrogen. Compounds like methane, butane, and hexane are hydrocarbons that are produced on burning of the fossil fuels.

What will happen if the coal reserves get depleted?

• Coal is being used as a major source of energy in industries as well as rural areas.

• Not only this, it serves various other purposes like the synthesis of synthetic oil, natural gas, coke, coal tar and coal gas.

• If the amount of coal gets depleted it would become much difficult for us to produce energy for various purposes. Hence, we must use coal in an efficient way.

What substances are released on the burning of coal?

1. Carbon dioxide

2. Carbon monoxide

3. Sulphur Dioxide

4. Nitrogen

5. Lead

6. Arsenic

7. Mercury

Petroleum

Figure 8 Petroleum

The term 'Petroleum' is derived from two words - 'Petra' which means 'rock' and 'oleum' which means 'oil'. It is mined from the rocks under the Earth.

Petroleum (also known as crude oil) is a fossil fuel formed from the remains of ancient marine organisms.

How is Petroleum and Natural Gas formed?

Figure 9 Formation of petrol and natural gas

• When the sea organisms die, their bodies sink to the bottom of the sea. With time, they get covered by the layers of sand and clay.

• Over millions of years, these remains get transformed in petroleum and natural gas due to high temperature, high pressure, and absence of air.

• When we dig oil wells, natural gas is above crude oil which in turn is above water. This happens because gas and oil are lighter than water and do not mix with it.

Refining of Petroleum

• Originally, petroleum is a mixture of many things, such as petrol, diesel, petroleum fas, paraffin wax, lubricating oil etc.

• It is a dark and oily liquid with an unpleasant odour.

• Refining of petroleum is the process by which different constituents of petroleum are separated.

• This process takes place in a petroleum refinery.

Constituents of Petroleum and their Uses

Figure 11 Constituents of Petroleum

Why Petroleum is called ‘black gold?

Petroleum is called 'black god' because it yields several substances that are commercially successful. The useful substances obtained from petroleum and natural gas are called 'petrochemicals'.

Petrochemicals are used in manufacturing:

• Synthetic fibres (such as Polyester, Nylon, Acrylic etc.),

• Detergents,

• Polythene, and

• Man-made plastics.

Natural gas also yields Hydrogen gas which is used in the production of fertilisers (such as urea).

Natural Gas

Figure 12 Natural Gas

Natural gas is a fossil fuel found naturally as a hydrocarbon gas mixture in the oil wells. Its main component is methane but it may also contain varying amounts of other higher alkanes (a group of elements). Gases like carbon dioxide, helium, nitrogen, and hydrogen sulphide are also found in natural gas in small percentages.

Why is Natural Gas important as a fossil fuel?

• Natural gas is considered important as this fossil fuel can easily be transported through pipes.

• It is stored as CNG which is used for several purposes and is also used as a starting material for manufacturing many chemicals and fertilisers.

• Natural Gas does not cause pollution and has high calorific value.

Compressed Natural Gas (CNG) is the natural gas stored under high pressure.

Why is CNG useful?

CNG is used as:

• Fuel to generate power

• Cleaner fuel for transport vehicles (less polluting than petrol and diesel)

• Fuel in homes and industries which can be supplied through pipes.

• CNG pipeline network already exists in Vadodara in Gujarat, some parts of Delhi and some other places.

Why is CNG considered as a cleaner fuel?

• Natural gas is considered a better fuel than coal and petroleum because it is cleaner.

• This means that it results in less amount of pollution that the other fossil fuels.

• Natural gas emits 50% less carbon dioxide, sulphur and nitrogen oxides in the air.

• However, it is not the best solution as there are better sources of energy present nowadays like solar energy.

Some Natural Resources are Limited

Fossil fuels, such as coal, petroleum, and natural gas cannot be created in the laboratory as it is not possible to create the natural conditions under which they are formed. Moreover, it takes thousands of years for them to be formed.

Consequences of the burning of fossil fuels

1. Increase in air pollution: The burning of fossil fuels results in the release of unburnt carbon particles in the air. These particles act as pollutants and increase air pollution. Fossil fuels release poisonous gases such as carbon monoxide and sulphur dioxide in the atmosphere.

2. Global Warming: Fossil fuels when burnt release large amounts of carbon dioxide in the air. As the amount of carbon dioxide increases it results in an increase in the global temperature of the earth and leads to global warming.

Why should we use fossil fuels economically?

1. They are available in limited quantities.

2. Burning these fuels also cause air pollution as well as global warming.

Hence, we should use these fuels economically to make sure that we can use them for a longer time, the risk of global warming gets reduced, and we can live in a cleaner environment.

How can we save petrol or diesel while driving?

According to the Petroleum Conservation Research Association (PCRA) in India, we can save petrol or diesel while driving by:

1. Drive at a constant and moderate speed.

2. Maintain tyre pressure at correct levels.

3. Switch off the engine when you are waiting( such as traffic light).

4. Do regular maintenance of your vehicle.

Why fossil fuels can last for 100 years only?

• Fossil fuels are exhaustible resources which mean that they are not present in abundant quantities on the earth.

• They take hundreds and thousands of years to replenish.

• The rate at which they are being consumed today is increasing at a rapid pace.

• It means that more amounts of fossil fuels are being used than it is being replenished.

• Hence, scientists claim that they can replenish completely in 100 years.