[Chemistry Class Notes] Formation of Fossil Fuels Pdf for Exam

What Are Fossil Fuels?

The earth is undergoing a variety of processes all the time. These processes are so slow that it takes millions of years to see their effect. Over a period of time, the layer of soil on the surface of the earth gets covered with newer layers, which keep getting deposited on top of the previous one. It happens that the remains of dead and decayed plants and organisms get trapped between these layers. When sediments are compressed together, it can lead to the formation of sedimentary rocks. These stratified rocks are soft and are often found to bear the impressions of dead plants and animals that get trapped in between them. These impressions are called fossils. 

Fossil fuels are called so because they are formed when the dead remains of living organisms get trapped between the layers of soil, and overtime get subjected to heat and pressure for a span of millions of years to form fuels. Fossil fuels are exhaustible, non-renewable, finite sources of energy. Using them in an injudicious manner can lead to their exhaustion. Formation of these fuels constitutes a part of the carbon cycle in nature. 

How is Coal Formed?

Millions of years ago, the earth was covered with lush, green vegetation. As these forests died, the soil bed was layered with plant remains. The debris got covered with another layer of soil, and the process continued. The buried vegetation got compressed under the effect of intense heat and pressure. The time period during which the formation of coal took place from the decaying vegetation is called the carboniferous age, and the process is called carbonization. 

Coal Formation Stages

The formation of coal is a four-stage process, depending on the conditions to which the plant debris was subjected. More the heat and pressure to which vegetation is subjected, better is the quality of coal. Superior quality coal is denser, has more carbon content, contains lesser moisture and has a better calorific value. The various stages of coal formation are described below:

1. Peat- Stage One

The formation of peat is the first stage in the formation of coal. It is a partially decomposed vegetable matter with very low carbon content. This incomplete decomposition leads to the formation of a slightly brown, organic mass called peat. It is fibrous and spongy, has high moisture content and is rarely used as a source of heat.

2. Lignite- Stage Two 

This is the second stage in which peat is subjected to more heat and pressure due to the weight of sediments getting accumulated above. It is darker in colour than peat, but the plant traces can still be spotted. 

3. Bituminous- Stage Three

When the pressure increases further, lignite becomes denser and more compact. At this stage, no traces of vegetation can be spotted. The carbon content increases and the moisture content decreases. Bituminous coal is the most widely used and easily available variety of coal used for domestic and industrial purposes. 

4. Anthracite- Stage Four 

It is the hardest and densest variety of coal. Since, the moisture is almost not there, anthracite burns with a short flame and produces little smoke. It has the maximum carbon content, and its calorific value is higher than the other varieties, making it the most superior quality of coal. 

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Uses of Coal

1. Coal has conventionally been used as a household and industrial fuel. Throughout the Industrial Revolution, coal was used as a source of energy.

2. Coal is used in thermal power plants to produce electricity. 

3. It is used for heating purposes.

How Is Petroleum Formed?

Petroleum is a thick, viscous, black liquid. Because of its value in today’s world, it is also called black gold. The formation of petroleum takes millions of years. It is formed when the dead remains of animals below the surface of the earth. As these dead remains are subjected to heat and pressure, they get decomposed and liquefied. This liquid form of organic matter is the petroleum or crude oil. It can be obtained by digging oil wells and refining the oil to yield several products or fractions. The dying aquatic animals get submerged, and get decomposed on the sea bed. They also form petroleum under similar conditions. 

Uses Of Petroleum

1. It is used to obtain a variety of reactions such as petrol, naphtha, paraffin wax, diesel etc. 

2. Its products are used as fuels in automobiles and industries. 

3. It is used in the manufacture of plastics and synthetic fibres and polymers.