Coal And Petroleum: Our Energy Sources | Class 8 Science CBSE

What Are Fossil Fuels and Why Are They Important?

Our planet provides us with many valuable materials, called natural resources. These can be broadly classified into two categories: renewable and non-renewable resources. Renewable resources, like sunlight, wind, and water, can be replenished naturally over a short period. However, resources such as coal, petroleum, and natural gas are considered non-renewable resources. This means they exist in limited quantities and take millions of years to form once they are used up.

Coal, petroleum, and natural gas are collectively known as fossil fuels. They are formed from the remains of dead plants and animals that were buried deep within the Earth's crust over millions of years. Under immense pressure and heat, these organic materials slowly transformed into the energy-rich substances we extract today. They are our primary sources of energy for transportation, electricity generation, heating, and powering various industries. Understanding coal and petroleum class 8 ncert concepts is crucial because our dependence on these finite resources highlights the importance of their careful use and the search for sustainable alternatives.

The Million-Year Journey: How Coal and Petroleum Are Formed

1. Formation of Coal: The Carbonisation Process — Imagine vast forests and swamps covering the Earth millions of years ago. When these plants died, they didn't completely decompose like they do today. Instead, they got buried under layers of soil and water. Over time, more layers accumulated, compressing the dead vegetation. The immense pressure from these layers, combined with the heat from the Earth's interior, slowly converted the plant matter into coal. This slow process of conversion of dead vegetation into coal is called carbonisation. That's why coal is mainly carbon.
2. Formation of Petroleum and Natural Gas — Petroleum (also known as crude oil) and natural gas have a different origin story. They were formed from tiny marine organisms (like algae and plankton) that lived in the sea millions of years ago. When these organisms died, their bodies settled at the bottom of the ocean and got covered by layers of sand and clay. Just like coal, the absence of air, high temperature, and high pressure transformed these dead organisms into crude oil and natural gas over millions of years. These fossil fuels are often found trapped between layers of impermeable rock.

Products from Coal and Petroleum and Their Uses

Both coal and petroleum are raw materials that need to be processed to obtain useful products. Let's look at what we get from them:

Products from Coal:
When coal is heated in the absence of air (a process called destructive distillation), it yields several useful products:

• Coke: A tough, porous, and black substance that is almost pure form of carbon. It's used in the manufacture of steel and in the extraction of many metals.
• Coal Tar: A thick, black liquid with an unpleasant smell. It's a mixture of about 200 substances. Products obtained from coal tar are used in manufacturing synthetic dyes, drugs, explosives, perfumes, plastics, paints, photographic materials, roofing materials, and even naphthalene balls.
• Coal Gas: Produced during the processing of coal to get coke. It's used as a fuel in many industries located near the coal processing plants.

Products from Petroleum:
Petroleum is a dark, oily liquid with an unpleasant odour. It's a complex mixture of various constituents like petroleum gas, petrol, diesel, kerosene, paraffin wax, lubricating oil, etc. The process of separating these different fractions from crude petroleum is called refining. This is done in a petroleum refinery using fractional distillation.

• Petroleum Gas (LPG): Used as fuel for home and industry.
• Petrol: Fuel for light motor vehicles (cars, motorcycles).
• Kerosene: Fuel for stoves, lamps, and jet aircraft.
• Diesel: Fuel for heavy motor vehicles (trucks, buses) and electric generators.
• Lubricating Oil: Used for lubrication in machinery.
• Paraffin Wax: Used in ointments, candles, and vaseline.
• Bitumen: Used in paints and road surfacing.

Many useful substances obtained from petroleum and natural gas are called petrochemicals. These are used in the manufacture of detergents, fibres (polyester, nylon, acrylic), polythene, and other man-made plastics.

Exam Tip: Why Conservation is Key!

When studying coal and petroleum class 8 ncert concepts, always remember the core message: these are non-renewable resources. This is a very common point for questions in exams. Emphasize in your answers that their formation takes millions of years, far beyond human lifespans, making them finite and irreplaceable. Therefore, conservation (reducing usage, exploring alternatives like solar and wind energy) is not just a good practice but a necessity for future generations. Also, clearly differentiate between the products obtained from coal (coke, coal tar, coal gas) and petroleum (LPG, petrol, diesel, kerosene, bitumen, etc.), and their primary uses.

Practice Questions with Solutions

• Q: What are fossil fuels? Give two examples. A: Step 1: Define fossil fuels as natural fuels formed over millions of years from the remains of dead organisms. Step 2: List examples like coal, petroleum, and natural gas. Final answer: Fossil fuels are natural fuels such as coal, petroleum, and natural gas, formed from the remains of dead plants and animals buried under the Earth's crust for millions of years.
• Q: Briefly explain the process of carbonisation. A: Step 1: Explain that carbonisation is the slow process by which dead vegetation is converted into coal. Step 2: Mention that this happens under high pressure and temperature, deep inside the Earth over millions of years. Final answer: Carbonisation is the slow process of conversion of dead vegetation into coal. This transformation occurs over millions of years under high pressure and temperature deep inside the Earth, making coal rich in carbon.
• Q: Name any three products obtained from petroleum and state one use for each. A: Step 1: Recall the refining process of petroleum and its various fractions. Step 2: List three products and their uses. Final answer: Three products obtained from petroleum and their uses are: 1. Petrol: Used as fuel for light motor vehicles. 2. Diesel: Used as fuel for heavy motor vehicles and electric generators. 3. LPG (Liquefied Petroleum Gas): Used as fuel for homes and industries.
• Q: Why are coal and petroleum considered non-renewable resources? A: Step 1: Explain the definition of non-renewable resources. Step 2: Relate it to the formation time of coal and petroleum. Final answer: Coal and petroleum are considered non-renewable resources because their formation takes millions of years. They exist in limited quantities on Earth, and once consumed, they cannot be replenished within a human timescale, making their supply finite.
• Q: What is meant by fractional distillation of petroleum? A: Step 1: Define petroleum as a mixture of various components. Step 2: Explain that fractional distillation is the process of separating these components based on their different boiling points. Final answer: Fractional distillation of petroleum is the process of separating the various components or fractions (like petrol, diesel, kerosene, etc.) from crude petroleum. This is done in a petroleum refinery based on the principle that different components of petroleum have different boiling points, allowing them to be collected at different temperatures.

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