One of the most significant chemical changes in our daily lives is burning substances to release energy. Substances that are burnt to produce energy are known as fuels. A fuel reacts with oxygen and burns to release energy. Commonly used fuels include natural gas, biogas, LPG, kerosene, diesel, firewood, coal and petrol.

Natural gas, coal and petroleum are called fossil fuels. Fossil fuels are carbon-rich precipitates formed over millions of years by decomposing the fossil remains of ancient plants and animals. Let us know more about two examples of fossil fuels: Coal and Petroleum.

Coal

Coal is hard as stone, black in colour and is mainly composed of carbon. Coal is one of the fuels used to cook food. Earlier, it was used in railway engines to produce steam to run the engine. It is also employed in thermal power plants to produce electricity. Apart from this, coal is also used as a fuel in various industries. It is also used to make products such as coke, coal tar and coal gas.

Fig: Coal

Formation of Coal

• 1. About 300 million years ago, there were dense forests in low lying areas on Earth.
• 2. Those forests got buried under the soil due to natural processes such as flooding.
• 3. Many layers of soil were deposited in these buried forests during the course of time.
• 4. As they sink deeper and deeper into the Earth, there is an increase in temperature.
• 5. Hence, all of those plants were converted into coal due to intense pressure and heat inside the Earth.
• 6. The process of conversion of this vegetation or plants into coal is called carbonization.
• 7. The plants buried under the soil undergo carbonization and change into coal.
• 8. Coal burns and produces mainly carbon dioxide when heated in the presence of the air.

Fig: Formation of Coal

Destructive Distillation of Coal

Heating coal in the absence of air (oxygen) is called destructive distillation of coal. This causes the decomposition of coal into different products that can be solid and gaseous. Some of the gases condense, whereas some dissolve in water.

Let’s see a small activity to understand the concept of destructive distillation of coal.

Aim: To carry out the destructive distillation of coal.

Materials required: Powdered coal, distilled water, boiling tubes, glass tubes, one-holed stopper, two-holed stopper, stand and Bunsen burner.

Procedure:

1. Keep powdered coal in boiling tube A.
2. Take distilled water in boiling tube B. Set up the apparatus as shown in the figure given below.
3. Heat the coal strongly with the help of a Bunsen burner.
4. After a few minutes, bring a lighted splint near the tip of the glass tube from tube B.

Fig: Destructive Distillation of Coal

Observation:

1. Vapours are formed due to the heating of coal. It passes through the water in tube B.
2. A thick black liquid, coal tar, settles at the bottom of tube B.
3. Ammonia dissolves in the water to form ammoniacal liquor.
4. The coal gas is released from tube B.
5. The presence of coal gas can be confirmed using a lighted splint as it burns with a yellow flame.
6. Coke is left in tube A as a black residue at the end of the process.

NCERT Solutions For 8th Science Chapter 5

Types of Coal

Coal is a natural black mineral. It is a mixture of carbon and carbon compounds containing hydrogen, oxygen, nitrogen and sulphur. There are four major types or ranks of coal. Rank refers to steps in a slow and natural process called coalification. Buried plant matter changes into an ever denser, drier, more carbon-rich, and more rigid material during this process. Based on carbon content composition, coal can be classified as follows:

• 1. Peat: Peat is the precursor of coal. It contains the highest percentage of moisture and has less than 40% carbon. Hence, it is the most inferior variety of coal. It produces a lot of smoke when it is burnt.
• 2. Lignite: Lignite coal, also known as brown coal, is the lowest grade coal with the most negligible concentration of carbon. Lignite is brown in colour and contains 40 – 60% of carbon. Like peat, it also produces a lot of smoke on being ignited. It can be used for power generation. Peat is converted into lignite due to increasing pressure and heat with the passage of time.
• 3. Bituminous: Bituminous coal is middle-rank coal between sub-bituminous coal and anthracite coal. When coal is buried very deep, the moisture gets expelled, leading to an increase in temperatures. This results in the formation of bituminous coal. Bituminous coal, also called soft coal, contains 60 – 80% carbon. The name ‘bituminous’ is derived from a liquid called bitumen released after heating. It is one of the most popular coals used in commercials for making coke (coking coal), gas coal, and steam coal.
• 4. Subbituminous: Subbituminous coal contains even less carbon and possesses a heat value. This coal is black in colour and is not shiny. It is generally formed in less time and found closer to the surface than higher grade coals. Therefore, it provides a convenient and efficient source of energy for thermal electricity generation.
• 5. Anthracite: The highest rank of coal, which is hard, brittle, and black lustrous coal, is usually referred to as hard coal. It includes a high percentage of fixed carbon and a low rate of volatile matter.

Practice Exam Questions

Fig: Types of Coal

Products of Coal and their Uses

• 1. Coke: It is a rigid, porous and black residue left at the end of the process. It is a pure form of carbon. Coke is a reasonably clean fuel and is therefore used as an industrial fuel. It is also used in iron extraction.
• 2. Coal tar: It is a complex liquid mixture of carbon compounds. It is a black and thick liquid with an unpleasant smell. It is a mixture of about 200 substances. Earlier, it was used to prepare organic compounds such as benzene and phenol. But, these are now obtained mainly from petroleum. Products obtained from coal tar are used as starting materials for manufacturing various substances used in everyday life and in industry, like synthetic dyes, drugs, explosives, perfumes, plastics, paints, photographic materials, roofing materials, etc. Interestingly, naphthalene balls used to repel moths and other Insects are also obtained from coal tar.
• 3. Ammoniacal liquor: It is an impure solution of ammonia, and it is also used in the waste and wastewater treatment, cold storage, and food and beverage industries as a stabilizer, neutralizer and source of nitrogen.
• 4. Coal gas: It is a mixture of hydrogen, methane, carbon monoxide and other gases. It was used as fuel earlier but has now been replaced by natural gas.

Fig: Products Obtained from Coal

Petroleum

We all know that petrol is used in light automobiles like motorcycles, scooters and cars, and heavy motor vehicles such as trucks and tractors run on diesel. Petrol and diesel are obtained from a natural resource called petroleum.

The word petroleum is derived from petra (rock) and oleum (oil), as they are mined from between the rocks under the Earth’s surface.

Petroleum, also called crude oil, is found as a liquid, deep underground or under the ocean beds, between layers of non-porous rocks. Different fuels and substances such as petroleum gas (liquefied and used as LPG (liquefied petroleum gas)), petrol, kerosene, diesel, fuel oil, lubricating oils and paraffin wax are collected from petroleum.

Petroleum has some extra benefits as compared to coal. Some of these are:

1. Petroleum is a high-density fuel.
2. The extraction process is much easier.
3. It can be stored, shipped, and piped to long distances.
4. It has a wider range of uses than coal.
5. Petroleum implements a stable energy resource.

Formation of Petroleum

Like coal, carcasses of dead plants and animals were buried at the bottom of the sea millions of years ago. They got covered with layers of sand and clay over the period of decomposition of organic matter. Due to high pressure, increased temperature and absence of air, they are transformed into petroleum.

Petroleum is obtained by digging oil wells in the Earth’s crust. When an oil well reaches a petroleum deposit or natural gas, if present, it is first released with tremendous pressure. The petroleum, which is also under pressure, then rises. It no longer rises naturally when the pressure of the petroleum falls. After this, water, gases, etc., are injected into the well to force more oil.

Fig: Formation of Petroleum

Fractional Distillation of Petroleum

The crude oil obtained from an oil well is a dark and viscous liquid. It is made up of a mixture of hydrocarbons (compounds made of hydrogen and carbon). This liquid is separated into its components by the process of fractional distillation.

• Fractional distillation is a process of separating a mixture of substances with different boiling points to get many components with similar boiling points. The individual components are called fractions.
• Each fraction is a mixture of substances with similar boiling points. For example, petrol is a mixture of hydrocarbons that is used without further separation. However, if pure substances are needed, further separation of each fraction is carried out.
• The process of separating crude oil into its components by fractional distillation is called refining.
• Refining is done in a cylindrical column called a fractionating column.
• Crude oil is heated to about 400^oC. The vapours that are formed are fed into the fractionating column.
• The lightest fraction is petroleum gas present at the top. Followed by petrol, naphtha, kerosene, diesel oil, lubricating oil and fuel oil.
• The residue left at the bottom is further distilled to give paraffin wax and asphalt.

Fig: Fractional Distillation of Petroleum

NCERT Solutions For 8th Science

Products of Petroleum and Their Uses

Petrol and diesel are two well-known products of petroleum. Apart from these two, a few more petroleum products are used for various purposes. Some of them are mentioned below, along with their uses:

Sr. No	Products of Petroleum	Usage
1.	Petroleum Gas (LPG)	Fuel for home (e.g., cooking) and some industries.
2.	Petrol	Motor fuel, aviation fuel and also a solvent for dry-cleaning.
3.	Kerosene	Fuel for stoves, lamps and jet aircraft.
4.	Diesel	Fuel for heavy motor vehicles, electric generators, etc.
5.	Heavy Oil or Lubricating Oil	Lubricants
6.	Fuel Oil	Ointments, candles, Vaseline, etc.
7.	Residue	Paints, road surfacing, etc.

Conservation of Coal and Petroleum

Some natural resources are available in limited quantities and can be finished by human activities; such resources are called exhaustible natural resources. Coal and petroleum are two examples of exhaustible natural resources. If these are not used wisely, they will not last for more than a few decades. Since they are widely used as energy sources around the globe, it is of absolute importance to think about their conservation.

Conservation is nothing but the process of using a natural resource more carefully to last for a more extended period. Coal and petroleum can be conserved by shifting to alternative or renewable energy sources like hydroelectric energy, wind energy, geothermal energy, tidal energy, etc. These alternatives will provide us with more environmentally friendly options for sustainable development and help delay the energy crisis that the world is about to face very shortly.

Summary

FAQs on Coal and Petroleum

Q.1. Where are coal and petroleum found? 
Ans: Coal exists in underground formations called “coal seams” or “coal beds.” And petroleum is found in vast underground reservoirs where ancient seas were located. Petroleum reservoirs can be found beneath land or the ocean floor.

Q.2. What is the difference between coal and petroleum?
Ans: Coal exists in a solid state, whereas petroleum exists in a liquid state. Coal emits smoke, ash, and other harmful gases, whereas the emission from petroleum is less than that of coal. The extraction of Coal is high, whereas the extraction of petroleum is low.

Q.3. What is the importance of coal and petroleum?
Ans: Coal and petroleum are the natural resources that are important sources of energy for us. Coal is used as a fuel in homes and industry or used to generate electricity at Thermal Power Plants. Petroleum products such as petrol and diesel are used as fuels in transport to run motorcycles, cars, buses, trucks, trains, ships and aeroplanes.

Q.4. How coal and petroleum oil are formed?
Ans: Coal and petroleum are formed due to decaying ancient plant life that lived millions of years ago. The matter of dead plants started to pile up, forming a substance called peat. Over time, heat and pressure from geological processes transformed these materials into coal and petroleum.

Q.5. Is coal found in the petroleum belt?
Ans: Yes, the coal is found in the petroleum belt.

Q.6. Is coal flammable or inflammable?
Ans: Coal is inflammable fuel because it can easily catch fire.

Q.7. What items are made from petroleum?
Ans: Various common products like aspirin, CDs/DVDs, clothes, dentures, lipsticks, shampoo, rugs, toothpaste, chewing gum, etc., are derived from petroleum hydrocarbons.