Class 8 CBSE Science Chapter 3: Coal and Petroleum

Introduction to Coal and Petroleum:

These notes of Coal and Petroleum ,cover all NCERT points, diagrams (you can draw fractionating column, coal products, petroleum refining), and important questions for exams. Good luck!

Natural resources are materials obtained from nature. They are of two types:

1. Inexhaustible natural resources – Present in unlimited quantity (e.g., sunlight, air, wind).
2. Exhaustible natural resources – Present in limited quantity and can be exhausted by human activities (e.g., forests, wildlife, minerals, coal, petroleum, natural gas).

Coal, petroleum and natural gas are fossil fuels – fuels formed from the dead remains of living organisms buried under the earth millions of years ago under high temperature and pressure.

1. Coal

Formation of Coal (Carbonisation)

• Millions of years ago, dense forests got buried under the soil due to earthquakes, floods, etc.
• New layers of soil kept depositing over them.
• Due to high pressure, heat and absence of air, the buried plant material slowly converted into coal.
• This slow process is called carbonisation.
• Coal is black, hard and mainly contains carbon.
• Hence coal is called a fossil fuel.

Types of Coal (based on carbon content and age)

1. Peat → Least carbon (~25-35%), lots of moisture, least heat.
2. Lignite → Brown coal, ~60% carbon.
3. Bituminous → Most common, ~70-85% carbon, used in industries and thermal power plants.
4. Anthracite → Highest carbon (~90-95%), hardest, burns with very little smoke.

Destructive Distillation of Coal When coal is heated strongly in the absence of air, it does not burn but produces many useful products. This process is called destructive distillation of coal.

Products of Coal

1. Coke → Almost pure carbon, used in manufacture of steel and extraction of metals.
2. Coal tar → Black thick liquid, used for making roads (bitumen), chemicals, naphthalene balls, paints, explosives, drugs, perfumes, etc.
3. Coal gas → Used as fuel in industries earlier, now replaced by natural gas.
4. Ammoniacal liquor → Used to make fertilisers.

2. Petroleum

Meaning Petroleum is a dark-coloured, foul-smelling thick liquid – a mixture of many hydrocarbons. The word “petroleum” means “rock oil” (petra = rock, oleum = oil).

Formation of Petroleum

• Petroleum was formed from dead marine organisms that got buried at the bottom of seas millions of years ago.
• Due to high pressure, heat and bacterial action in the absence of air, they were converted into petroleum and natural gas.
• Petroleum and natural gas are found trapped between porous and non-porous rocks.

Refining of Petroleum Petroleum is a mixture of many compounds. The process of separating these compounds using their different boiling points is called refining. It is done in a petroleum refinery by fractional distillation.

Fractional Distillation of Petroleum (products obtained from lower to higher temperature fractions)

Constituents of Petroleum

• Mainly hydrocarbons (compounds of carbon and hydrogen).
• Also contains small amounts of sulphur, nitrogen and oxygen compounds.

3. Natural Gas

• Found along with petroleum deposits or sometimes separately (e.g., in Tripura, Rajasthan, Krishna-Godavari delta).
• Mainly contains methane (CH₄) (95%) with small amounts of ethane, propane, etc.
• Convenient fuel because it burns cleanly, produces very little smoke.
• Transported through pipelines.
• Stored under high pressure as CNG (Compressed Natural Gas) – used as fuel in vehicles (eco-friendly, less polluting).
• LPG (Liquefied Petroleum Gas) – Mixture of butane and propane, stored in liquid form in cylinders.

Advantages of CNG over Petrol/Diesel

• Burns completely → no unburnt carbon particles.
• No lead or sulphur → less air pollution.
• Cheaper and cleaner fuel.

4. Exhaustible Nature of Fossil Fuels

• Coal and petroleum took millions of years to form.
• We are consuming them at a very fast rate.
• Known reserves will last only a few hundred years.
• They are non-renewable resources.

5. Conservation of Coal and Petroleum

We must conserve fossil fuels because:

1. They are limited in quantity.
2. Burning them causes air pollution (CO₂, SO₂, smoke, etc.).
3. CO₂ causes global warming (greenhouse effect).

Ways to Conserve

1. Use public transport, carpooling, cycling instead of personal vehicles.
2. Switch off engines at traffic lights.
3. Use CNG vehicles.
4. Use stairs instead of lifts for a few floors.
5. Use pressure cookers, solar cookers.
6. Walk or use bicycles for short distances.
7. Use LED bulbs, star-rated appliances to save electricity (thus saving coal used in power plants).

PCRA Tips (Petroleum Conservation Research Association, India)

• Drive at moderate speed.
• Maintain correct tyre pressure.
• Regular servicing of vehicles.
• Switch off engine at red lights.

Key Terms to Remember

• Fossil fuels → Coal, petroleum, natural gas.
• Carbonisation → Slow conversion of dead vegetation into coal.
• Destructive distillation → Heating coal in absence of air.
• Refining → Separation of petroleum into useful fractions.
• Fractionating column → Tall tower in refinery where fractional distillation takes place.
• CNG → Compressed Natural Gas.
• LPG → Liquefied Petroleum Gas.

Summary Table

Conclusion Coal and petroleum are precious natural resources formed over millions of years. We must use them judiciously so that future generations can also benefit from them. Conservation today will ensure a cleaner and sustainable tomorrow.

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