Big picture
Coal, petroleum and natural gas are fossil fuels formed from ancient organic matter over geological time. People use them for energy and as raw materials for chemicals. Their formation is extremely slow compared with their present consumption, so conserving them is necessary even when new deposits are discovered.
A school bus, a cooking stove and a road surface may depend on different products of these resources. Understanding their origin, processing and uses helps explain why “petroleum” does not mean only petrol and why conserving fuel also conserves a valuable industrial resource.
Learning goals
Distinguish exhaustible and practically inexhaustible natural resources.
Explain the formation of coal, petroleum and natural gas.
Describe coal processing and the uses of coke, coal tar and coal gas.
Explain petroleum refining and identify major products and uses.
Compare LPG, CNG and natural gas without treating them as identical.
Explain pollution, conservation and responsible use with numerical examples.
Core ideas
1. Resources and availability
A natural resource is a useful material or source of energy obtained from nature. Exhaustible resources occur in limited amounts and can be depleted by use. Coal, petroleum, natural gas and mineral deposits are examples. Sunlight is treated as practically inexhaustible for ordinary human use, though access to it varies by place and time.
Renewable does not mean impossible to damage. Forests can regrow, but cutting faster than regrowth can destroy them. Fossil fuels are non-renewable on human timescales because their formation takes vastly longer than a human lifetime. A resource being underground does not imply that it will replenish as quickly as it is extracted.
Worked comparison. A hypothetical school uses 120 units of a stored resource each month but replaces only 30 units. Net depletion = 120 − 30 = 90 units per month. The example shows why rate of use matters; it is not an estimate of fossil-fuel formation.
2. Formation of coal
Ancient plant material accumulated in swampy forests. Burial under sediments limited decay and exposed it to increased pressure and temperature over a very long time. It gradually changed into coal, becoming richer in carbon. This slow conversion of dead vegetation into coal is called carbonisation.
Coal is generally a dark, solid fuel containing carbon along with other substances. It is not pure carbon. Coal seams are extracted through mines; the deposit's depth and geology influence the mining method. Mining also affects land, water and worker safety, so extraction is not simply collecting a harmless black stone.
For a diagram, imagine layers of sediment above a buried plant-rich layer. Label ancient vegetation, overlying sediments, heat and pressure during burial, and the resulting coal seam. The diagram represents a long natural process, not an experiment that can be completed in a classroom.
3. Uses and processing of coal
Coal is burned in thermal power stations to produce heat. Heat produces steam that drives turbines linked to generators. The energy pathway is chemical energy → heat → mechanical movement → electrical energy. Coal is also processed to obtain useful substances rather than only burned directly.
Heating coal strongly in the absence of air produces coke, coal tar and coal gas. Excluding air prevents the coal simply burning away during this processing. This is often described as destructive distillation of coal in school science.
Product | Main character | Uses |
|---|---|---|
Coke | Tough, porous solid, almost pure carbon | Steel manufacture and metal extraction |
Coal tar | Thick dark mixture of many substances | Starting material for several chemicals |
Coal gas | Combustible gaseous mixture | Fuel near some coal-processing plants |
Do not confuse coke with the drink of a similar name. Coal tar is a mixture, not one pure compound. It historically supplied chemicals used for dyes, drugs, perfumes, plastics and other products; many such chemicals can now also be made from petroleum-based feedstocks.
4. Coal tar and road materials
School texts contrast coal tar with bitumen, a petroleum product now widely used as a binder in road surfacing. A dark road surface is not evidence that it was made from coal tar. Bitumen binds mineral aggregates; it is not simply liquid petrol spread on a road.
A useful classification question asks whether coke, coal tar and bitumen all arise from coal processing. The answer is no: coke and coal tar are coal products, whereas bitumen comes from petroleum refining. Similar appearance or common use does not establish the same origin.
5. Formation and occurrence of petroleum
Petroleum formed mainly from ancient marine organisms buried beneath sediments. Over long periods, heat and pressure transformed organic material into hydrocarbons. The resulting fluids could migrate through porous rock and become trapped below relatively impermeable layers.
In a simplified reservoir diagram, show an impermeable cap rock above a porous reservoir. Label natural gas at the top, petroleum below it and water lower down. This layering reflects differences in density and the particular reservoir structure. Petroleum is held in rock pores rather than necessarily in a giant underground cave.
Indian petroleum-producing regions include Assam, Gujarat and the offshore Mumbai High area. These are examples for locating producing regions on an India map, not a complete or ranked list of deposits. Petroleum can be extracted on land or offshore using suitable drilling equipment.
6. Refining separates a mixture
Crude petroleum is a mixture of hydrocarbons and other substances. Refining separates and processes it into useful fractions. In the introductory model, crude oil is heated and fractions are separated according to different boiling ranges. Industrial refineries include additional purification and conversion processes.
A simple diagram shows a heated feed entering a fractionating column, with a temperature gradient and outlets at different levels. More volatile fractions leave higher regions, while heavier material remains lower. Do not label every fraction as a pure chemical: a fraction usually contains a range of compounds.
Petroleum fraction/product | Common use |
|---|---|
Petroleum gas, supplied as LPG | Domestic and industrial fuel |
Petrol | Fuel for suitable engines; also chemical feedstock uses |
Kerosene | Fuel, including specified aviation turbine fuel applications |
Diesel | Fuel for diesel engines and some generators |
Lubricating oil | Reduces friction between moving surfaces |
Paraffin wax | Candles, polishes and other products |
Bitumen | Road binder and certain waterproofing uses |
Petroleum is sometimes called black gold because of its economic value and range of useful products. The phrase is figurative, not a statement that petroleum contains gold.
7. Natural gas, CNG and LPG
Natural gas is a gaseous fossil fuel consisting mainly of methane. It may occur with petroleum or in separate deposits. Pipelines can carry it to industries and consumers. It is also a feedstock for chemicals and fertiliser production.
CNG, compressed natural gas, is natural gas stored at high pressure. LPG, liquefied petroleum gas, mainly contains propane and butane and is stored as a liquid under pressure. They are not the same mixture. Gas-cylinder pressure alone does not identify the gas as natural gas.
Compared with coal and some liquid fuels, well-operated gas systems can produce less soot and certain local air pollutants. They are still fossil fuels: combustion releases carbon dioxide, and methane leakage has a warming effect. “Cleaner” does not mean “pollution-free”.
8. Combustion, equations and emissions
Complete combustion of carbon can be represented by C + O₂ → CO₂. Complete combustion of methane is CH₄ + 2O₂ → CO₂ + 2H₂O. Count atoms to verify the methane equation: one carbon, four hydrogen and four oxygen atoms occur on each side.
Insufficient oxygen can produce carbon monoxide and soot. Carbon monoxide is poisonous. Sulphur-containing fuels can produce sulphur oxides, and combustion can also contribute to nitrogen oxides and particulate pollution. Carbon dioxide from fossil-fuel use increases atmospheric greenhouse-gas concentrations.
Do not burn coal tar, petrol or gas samples as a classroom identification test. Their behaviour can be explained using teacher-approved demonstrations, diagrams and recorded observations. For a safe observational task, compare labels or documented uses of petroleum products without opening fuel containers.
9. Conservation and efficient use
Conservation means avoiding waste while meeting needs efficiently. Walking or cycling for suitable short journeys, shared transport, maintained vehicles, reduced idling and efficient appliances can reduce fuel use. The appropriate action depends on safety, access and circumstances.
Worked example. A school vehicle normally uses 18 litres on a route. Improved scheduling reduces use to 15 litres. Saving = 18 − 15 = 3 litres. Percentage saving = 3 ÷ 18 × 100 = 16⅔%. At an assumed price of ₹90 per litre, monetary saving = 3 × 90 = ₹270. The price is a hypothetical exercise value, not a current market quotation.
A saving calculation should compare the same service or journey. Using less fuel by cancelling essential access is different from delivering the same service more efficiently. Assess the full context instead of treating every reduction as automatically fair.
10. Resource decisions and exam reasoning
A claim that new drilling makes petroleum renewable confuses finding additional stock with creating it quickly. A claim that all petroleum must be burned ignores its use as a chemical raw material. A claim that electric devices never depend on fossil fuels overlooks the source of their electricity.
For a case study, trace the resource from formation to extraction, processing, use and waste or emissions. If asked why conservation matters, give both finite supply and environmental consequences. If asked to compare products, state origin, properties and use rather than listing names without explaining the connection.
A reliable approach to questions
Identify the resource, product or process named.
Separate formation, extraction, refining and combustion.
Link each product to its source and suitable use.
For equations, balance each element and distinguish complete from incomplete combustion.
For savings, state the original amount, reduction and denominator.
Check that “cleaner”, “available” and “renewable” have not been treated as identical ideas.
Connections that matter
Combustion and Flame explains fuel burning, oxygen supply and incomplete combustion.
Conservation links resource use with long-term environmental effects.
Materials and manufacturing use petroleum and coal products as industrial feedstocks.
Common mistakes
Calling coal pure carbon: coke is almost pure carbon; coal contains other substances.
Treating petroleum as petrol only: petrol is one refined product.
Identifying LPG with CNG: their main constituents and storage conditions differ.
Calling cleaner gas renewable: origin and replenishment determine renewability.
Revision checklist
I can distinguish finite fossil fuels from rapidly replenished resources.
I can explain coal and petroleum formation without treating it as a short process.
I can compare coal products and petroleum fractions.
I can describe a reservoir and a simple refining column.
I can distinguish LPG, CNG and natural gas.
I can explain emissions and calculate a fuel saving.