Coal and Petroleum
Class 8 Science Short Notes
Key Words
Minerals
Useful chemicals found in lithosphere.
Fractional Distillation
Separation of petroleum into useful products by heating in a tall tower.
Off-shore Drilling
Drilling for petroleum under the sea-bed.
Energy Crisis
Depletion of energy sources due to fast consumption.
Natural Resources
- Inexhaustible – Unlimited in nature, not likely to exhaust (e.g., Sunlight, Air, Water).
- Exhaustible – Limited in nature, can exhaust (e.g., Coal, Petroleum, Natural gas, Forests, Minerals, Wildlife).
Fossil Fuels
- Coal, petroleum, natural gas – formed from dead organisms over millions of years under high temperature & pressure, absence of air.
- Cannot be made in lab.
Coal
- Found deep in earth as coal beds (contain methane).
- Main Indian deposits: Jharkhand (Jharia, Bokaro), Odisha, Madhya Pradesh, West Bengal (Raniganj).
Formation (Carbonisation)
Wood → Peat → Lignite → Bituminous coal → Anthracite
- Carbonisation – Slow conversion of plant material to coal under high temperature, high pressure, absence of air.
- Calorific value ↑ with carbon % (lowest in wood, highest in anthracite).
Types of Coal
Peat
Approx. ~30% carbon
Light brown, least carbon
Lowest grade, high moisture, low heating value
Lignite
Approx. ~38% carbon
Brown, soft coal
Brown coal, slightly better fuel than peat
Bituminous
Approx. ~65% carbon
Black, household/industry use
Black, higher heating value, used in industries
Anthracite
Approx. ~90% carbon
Bright black, hard, highest carbon & calorific value
Hard, shiny, burns clean with high heat output
Uses of Coal
- Fuel
- Manufacture of coke, coal tar, coal gas
- Making synthetic petrol, synthetic natural gas
- Source of organic compounds: benzene, toluene, phenol, naphthalene (naphthalene balls)
- Metal extraction
Destructive Distillation of Coal
- Heating coal (esp. Bituminous) at 1000–1400°C without air
Products
Coke
98% carbon (Coal – Moisture – Volatile matter)
Uses: Domestic fuel, reducing agent in metallurgy, make fuel gases (water gas = CO + H₂, producer gas = CO + N₂), make carbides (CaC₂, SiC, Al₄C₃)
- Calcium carbide – Raw material for petrochemical industry
- Aluminium carbide – Petrochemical raw material
- Silicon carbide (SiC) – Very hard, used as abrasive
Coal Tar
Black, viscous, bad smell, ~200 compounds
Uses: Fractional distillation gives dyes, drugs, explosives, perfumes, organic compounds
Naphthalene balls made from naphthalene in coal tar
Coal Gas
Main gases: H₂ (38–55%), CH₄ (15–22%), CO (4–15%), N₂ (2–20%)
Uses (earlier): Street lighting, domestic fuel
Uses (now): Industrial heating, inert/reducing atmosphere in metal extraction
Ammoniacal Liquor
Water containing ammonia & ammonium salts
Important Facts to Remember
- Inexhaustible: Sunlight, air, water
- Exhaustible: Forests, wildlife, coal, petroleum, natural gas
- Highest carbon content – Anthracite
- Lowest carbon content – Peat
- Naphthalene balls – From coal tar
- SiC (Silicon carbide) – From coke, used as abrasive
- Calcium carbide – From coke, for petrochemicals
- Producer gas – CO + N₂
- Water gas – CO + H₂
Petroleum, Natural Gas & Conservation
Petroleum
- Meaning – "Oil of rocks" (petro = rock, oleum = oil)
- Appearance – Viscous, dark (amber–black), fluorescent liquid, unpleasant odour, lighter than water
- Also called – Crude oil (cannot be used directly, needs refining)
Composition
- Mixture of many hydrocarbons + organic compounds with N, O, S
- Contains saline water & silt
Formation
- From marine organisms' remains → buried under sand/clay → millions of years → high temperature, high pressure, absence of air, bacterial action
- Moves through porous rocks, trapped under impervious rocks
- Natural gas forms a cover over petroleum
Mining
- Depth: few hundred m to 2–3 km
- Drilling holes + pipes → oil gushes out due to gas pressure → later pumped
- India locations – Gujarat (Ankleshwar, Kalol), Assam (Rudrasagar, Lakwa), Bombay High, Godavari & Kaveri deltas
Refining of Petroleum (Fractional Distillation)
- Done in tall steel fractionating tower in refineries (India: Koyali, Mumbai, Cochin, Chennai, Vizag, Haldia, Barauni, Guwahati, Digboi, Mathura)
- Crude oil heated ~400°C → vapours rise, condense at different heights based on boiling point
Main Fractions & Uses
| Fraction | Carbon atoms | Boiling range | Uses |
|---|---|---|---|
| Petroleum gas (LPG) | 1–4 | up to 40°C | Domestic fuel, carbon block |
| Petrol/Light naphtha | 5–10 | 40–170°C | Automobile fuel, dry cleaning solvent |
| Kerosene | 10–12 | 170–250°C | Domestic fuel, illuminant |
| Diesel | 13–15 | 250–350°C | Trucks, buses, pumps, generators |
| Fuel oil | 15–18 | 350–400°C | Industrial fuel (boilers, furnaces) |
| Lubricating oil | 17–20 | Residue | Machine lubricant |
| Paraffin wax | 20–30 | Residue | Candles, shoe polish, grease |
| Asphalt | — | Residue | Roads |
Petroleum products used as fuels – LPG, Petrol, Kerosene, Diesel, Fuel oil
Not used as fuels – Petroleum ether, Lubricating oil, Grease, Petroleum jelly, Paraffin wax, Pitch
Natural Gas
- Definition – Gaseous lower hydrocarbons (mainly methane) occurring deep inside earth, alone or above crude oil
- Properties – Burns with blue smokeless flame, no ash, high calorific value (~55 kJ/g)
Uses
- Domestic/industrial fuel
- Making hydrogen (from methane at 1250 K + catalyst) → ammonia → urea
- Making carbon black (reinforcing agent in tyres, tubes)
- Raw material for petrochemicals & fertilizers
- India deposits – Tripura, Rajasthan, Maharashtra, Krishna-Godavari delta
Compressed Natural Gas (CNG)
- Natural gas compressed under high pressure for transport via pipelines
- Used as automobile fuel (cars, buses, scooters)
- Clean fuel – CO₂ & water formed, no ash, no smoke
Consequences of Excessive Mining & Use
Energy Crisis
Reserves will deplete (Petroleum ~50 years left, Coal ~150–200 years)
Earth Structure Impact
Hollow spaces → land collapse, minor earthquakes
Pollution Effects
- CO₂ → Greenhouse effect → global warming, polar ice melt, floods, monsoon change
- CO → Poisonous, binds haemoglobin → suffocation, death
- SOₓ & NOₓ → Respiratory issues, acid rain → corrosion
Petroleum Conservation Tips (PCRA)
- Drive at constant moderate speed
- Avoid frequent accelerator use
- Switch off engine at traffic lights/wait
- Maintain correct tyre pressure
- Service vehicle regularly
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