Coal and Petroleum — Class 8

Coal and Petroleum — Class 8

Coal and petroleum are the most important fossil fuels we use today. They power our buses, light our homes, run our factories, and produce the plastics in our toothbrushes and cricket bats. But these fuels are non-renewable — once we use them up, they’re gone for centuries. So understanding what they are, how they formed, and why we should use them wisely is one of the most important lessons in Class 8 Science.

In this chapter, let’s understand the difference between exhaustible and inexhaustible resources, see how coal and petroleum form, learn about the products we get from them, and figure out what we can do to make them last longer.

Two Types of Natural Resources

Inexhaustible (renewable) resources are those that won’t run out as we use them — at least not on a human timescale.

Examples: Sunlight, air, water (in most contexts), wind.

Exhaustible (non-renewable) resources can run out. Once used, they take millions of years to form again.

Examples: Coal, petroleum, natural gas, forests (if cut faster than regrown).

How Did Coal Form?

Millions of years ago, dense forests covered low-lying wetlands. Trees and plants died, fell into the swampy waters, and were buried under layers of sediment. Over millions of years, with intense heat and pressure but no oxygen, the buried plant matter slowly transformed into coal.

This long process is called carbonisation — the gradual conversion of plant matter to carbon-rich coal.

Because coal forms from ancient living organisms (plants), it’s called a fossil fuel. The same is true for petroleum, except petroleum forms from ancient marine organisms.

Products from Coal

When coal is heated in the absence of air (called destructive distillation), it gives several useful products:

Coke — A nearly pure form of carbon. Hard, porous, black. Used in steel manufacturing and as a reducing agent.

Coal tar — A thick black liquid. Used to make synthetic dyes, drugs, plastics, paints, perfumes, photographic materials, roofing materials. Naphthalene balls (used to keep moths away from clothes) are made from coal tar.

Coal gas — A mixture of methane, hydrogen, and carbon monoxide. Used as a fuel in industries.

How Did Petroleum Form?

Hundreds of millions of years ago, tiny sea organisms (plankton, algae, bacteria) died and settled at the bottom of seas. Over geological time, these remains were buried under sand and clay. Heat, pressure, and the absence of oxygen converted them slowly into petroleum (oil) and natural gas.

This is why we drill for petroleum mostly under former sea beds — places that were once oceans millions of years ago.

Products from Petroleum

Crude petroleum is a black, smelly liquid. It’s a mixture of many substances, which we separate by fractional distillation — heating the crude oil and collecting different products as they boil off at different temperatures.

Natural Gas

Natural gas is mostly methane ($CH_4$). Found above petroleum deposits or as separate fields. Stored and transported as CNG (Compressed Natural Gas) — used as a cleaner fuel for buses (Delhi switched to CNG buses in 2002 to reduce pollution) and households.

CNG burns cleaner than petrol or diesel, releasing fewer pollutants.

Why Should We Conserve Fossil Fuels?

1. They are exhaustible. India’s coal reserves may last about 200 years; petroleum reserves much less. Once used, no replacement for millions of years.

2. Burning them causes air pollution — sulphur dioxide, carbon monoxide, particulate matter, nitrogen oxides. These cause acid rain, respiratory diseases, and global warming.

3. Burning them releases greenhouse gases (mainly $CO_2$), which cause climate change.

How Can We Conserve?

• Use public transport instead of private cars
• Carpool when possible
• Switch off vehicles at red lights for long waits
• Maintain vehicles regularly for fuel efficiency
• Use bicycles for short distances
• Switch off lights and appliances when not in use
• Use energy-efficient appliances
• Insulate buildings to reduce heating/cooling energy

The Petroleum Conservation Research Association (PCRA) in India gives many of these recommendations and runs awareness campaigns each year.

Common Mistakes to Avoid

Practice Questions

1. What is meant by an exhaustible natural resource? Give two examples.

2. Name the three main products obtained from destructive distillation of coal.

3. What is petroleum refining? Why is it necessary?

4. List five fractions obtained from petroleum and one use of each.

5. What is the chemical name and formula of the main constituent of natural gas?

6. Why is CNG considered a better fuel than petrol or diesel?

7. Suggest five ways to conserve petroleum products.

8. Where does coal come from, and how is it formed?

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