Kitchen fires, vehicles and most of India's electricity run on fuels — mostly coal, petroleum and natural gas, formed from living things buried millions of years ago. Burning them is combustion. Petroleum also gives us synthetic fibres and plastics. Exams ask about LPG, CNG and methane, fire control, flame zones, polymers like PVC, and chemicals used every day.
On this page you will learn:
- Coal, petroleum and natural gas, and their products
- Gas fuels: LPG, CNG, biogas and the many names of methane
- Combustion, ignition temperature and putting out fires
- Flame zones and calorific value
- Polymers: fibres and plastics
- Chemicals and materials of daily life
150,000
kJ/kg from hydrogen
Highest calorific value
CH4
Methane
CNG, biogas, marsh gas
3
Needs of a fire
Fuel, air, heat
Coal, petroleum and natural gas
Rule in one line: fossil fuels formed from dead organisms over millions of years and cannot be replaced.
KEY TERM
Carbonisation
Dead plants buried deep under the earth, at high temperature and pressure, slowly turned into coal. This is carbonisation. Because coal came from living things, it is a fossil fuel. Petroleum and natural gas formed in a similar way from tiny sea organisms.
Dead plants→Buried→Heat + pressure→Coal
| Product of coal | What it is | Uses |
|---|---|---|
| Coke | Tough, porous, almost pure carbon | Making steel |
| Coal tar | Thick black liquid, a mixture of about 200 substances | Dyes, drugs, explosives, paints, naphthalene balls |
| Coal gas | Gas given off while making coke | Fuel in nearby factories |
| Part of petroleum | Main use |
|---|---|
| LPG | Cooking fuel |
| Petrol | Cars and scooters; dry-cleaning solvent |
| Kerosene | Stoves, lamps, jet aircraft |
| Diesel | Heavy vehicles, generators |
| Lubricating oil | Smoothing machines |
| Paraffin wax | Candles, vaseline, ointments |
| Bitumen | Road surfaces, paints |
QUICK CHECK
PYQ · PSSSB Patwari 2023 — Petroleum is also famous as
Tap an option to answer
Answer: C — Crude oil
Unrefined petroleum is crude oil. Petrol is only one of the products made from it.
QUICK CHECK
PYQ · PPSC NE 2019 — Which one of the following statements about Compressed Natural Gas (CNG) is not true ?
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Answer: B — It is obtained during refining of crude oil.
CNG comes from gas wells and oil fields, not from refining crude oil. LPG is the gas from refining. PPSC RO and TA 2019 asked the same.
QUICK CHECK
PYQ · Punjab Police SI 2023 — Why is CNG considered a better fuel than petrol and diesel?
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Answer: B — It burns more efficiently.
Being a gas, CNG mixes well with air and burns almost completely, with less smoke and pollution.
LPG, biogas and the names of methane
Rule in one line: cooking gas is butane and propane; marsh gas, gobar gas and CNG are mostly methane.
| Name | Where it comes from | Main gas |
|---|---|---|
| Marsh gas | Rotting plants under marsh and paddy water | Methane, CH4 |
| Gobar gas (biogas) | Cattle dung rotting without air | Methane, with carbon dioxide |
| Firedamp | Coal mines | Methane |
| CNG | Natural gas wells | Methane |
| LPG (cooking gas) | Refining crude oil | Butane and propane |
QUICK CHECK
PYQ · PPSC OHE 2016 — Cooking gas is a mixture of:
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Answer: B — Butane and propane
LPG is mainly butane and propane, liquefied under pressure in the cylinder.
QUICK CHECK
PYQ · PPSC SEVE 2016 — Which one of the following is known as Marsh gas?
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Answer: B — CH4
Methane (CH4) forms when plants rot under water in marshes and paddy fields, so it is called marsh gas.
Combustion and fire control
Rule in one line: fire needs fuel, air and heat; take away any one and the fire goes out.
Combustion is a chemical reaction in which a substance joins with oxygen and gives off heat, often with light. The chemical energy stored in the fuel turns into heat (thermal) energy.
THE THREE NEEDS OF A FIRE
- 1FuelWood, LPG, petrol
- 2AirOxygen supports burning
- 3HeatEnough to reach the ignition temperature
KEY TERM
Ignition temperature
The lowest temperature at which a substance catches fire. A paper cup of water does not burn over a flame, because the water takes the heat away. Substances that catch fire very easily — petrol, alcohol, LPG — are inflammable.
| Type of combustion | What happens | Example |
|---|---|---|
| Rapid | Burns quickly with heat and light | LPG on a stove |
| Spontaneous | Catches fire on its own | White phosphorus in air |
| Explosion | Sudden burning with heat, light and sound | Firecrackers; methane and air in coal mines |
| Kind of fire | Use water? | Why |
|---|---|---|
| Wood, paper, cloth | Yes | Water cools the fuel below its ignition temperature |
| Electrical | No | Water conducts electricity; risk of shock |
| Oil or petrol | No | Water sinks below the oil, which keeps burning on top |
QUICK CHECK
PYQ · PPSC EO 2018 — Combustion is the process of conversion of which of the following energies?
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Answer: B — chemical → thermal
A fuel stores chemical energy in its bonds; burning releases it as heat (and light). PPSC SSO 2018 asked the same.
QUICK CHECK
PYQ · PPSC NE 2019 — Most of the explosions in mines occur due to the mixing of
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Answer: B — Methane with air
Coal seams give off methane (firedamp). Mixed with air, it explodes at the smallest spark. PPSC RO and TA 2019 asked the same.
Flame and calorific value
Rule in one line: the outer, blue part of a flame is hottest; hydrogen gives the most heat per kilogram.
| Zone | Colour | Burning | Heat |
|---|---|---|---|
| Innermost | Dark | Unburnt wax vapour | Least hot |
| Middle | Yellow, bright | Partial | Moderate |
| Outermost | Blue, not bright | Complete | Hottest |
Calorific value of fuels
HARM FROM BURNING FUELS
Incomplete burning gives carbon monoxide, a deadly gas — never sleep in a closed room with a coal fire. Extra carbon dioxide adds to global warming. Sulphur and nitrogen oxides dissolve in rain and cause acid rain.
Polymers: fibres and plastics
Rule in one line: a polymer is a giant molecule made of many small repeating units.
KEY TERM
Polymer
'Poly' means many and 'mer' means part. Small units called monomers join into long chains. Polythene is made of thousands of ethene units. Natural polymers exist too: cotton is cellulose, and proteins are polymers of amino acids.
Monomer→+ monomer→+ monomer …→Polymer
| Fibre | Made from / known as | Uses |
|---|---|---|
| Rayon | Wood pulp; artificial silk | Bed sheets, carpets |
| Nylon | First fully synthetic fibre | Ropes, parachutes, toothbrushes, socks |
| Polyester | Terylene and PET are forms of it | Wrinkle-free clothes, bottles |
| Acrylic | Artificial wool | Sweaters, shawls, blankets |
QUICK CHECK
PYQ · PPSC ICS 2016 — A large molecule with many repeating structural units is a
Tap an option to answer
Answer: A — Polymer
A polymer is the general name. A monomer is one unit; polythene and polypeptides are particular polymers.
QUICK CHECK
PYQ · Punjab Police SI 2016 — The term PVC used in the plastic industry stands for
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Answer: B — polyvinyl chloride
PVC is polyvinyl chloride, a polymer of vinyl chloride used for pipes, cable covers and flooring.
Chemicals and materials of daily life
Rule in one line: match each chemical or material to the job it does.
| Item | What it is | Used for |
|---|---|---|
| Aspartame, saccharin | Artificial sweeteners | Sugar-free drinks and sweets |
| Mosquito coils, mats, liquids | Insecticides | Killing or driving away mosquitoes |
| Silicon carbide (carborundum) | A very hard compound | Cutting and grinding hard things |
| Concrete, fibreglass | Composites | Buildings; boats, helmets, tanks |
| Cement | Made by heating limestone and clay; gypsum is added | Binding bricks and concrete |
| Glass | Made mainly from sand (silica) | Windows, bottles, optical fibres |
QUICK CHECK
PYQ · Punjab Police Constable 2024 — Aspartame is a compound of amino acids named aspartic acid and a form of phenylalanine, which is used as a/an ________.
Tap an option to answer
Answer: A — Artificial Sweetener
Aspartame is far sweeter than sugar, so a tiny amount sweetens 'diet' and sugar-free products.
QUICK CHECK
PYQ · PPSC EO 2018 — The mosquito repellent (coils, mats and liquids) that we generally use in our homes are:
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Answer: A — Insecticides
Mosquitoes are insects, so these products are insecticides. Germicides kill germs; weedicides kill weeds. PPSC SSO 2018 asked the same.
QUICK CHECK
PYQ · PPSC EO 2018 — In which of following activities silicon carbide is used?
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Answer: D — Cutting very hard substances
Silicon carbide is one of the hardest substances, so it is used in grinding wheels and cutting tools. Casts for statues use plaster of Paris.
QUICK CHECK
PYQ · PPSC AA 2022 — Concrete and fiber glass are_________
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Answer: A — Composite materials
Each is made of two or more materials joined together, which is what a composite is.
Traps and practice
Last revision — where the options try to fool you.
COMMON TRAPS
- CNG comes from gas wells, not from refining crude oil; LPG comes from refining.
- Cooking gas = butane + propane; marsh gas, gobar gas, CNG = methane.
- Mine explosions: methane + air, not hydrogen + oxygen.
- Combustion turns chemical energy into heat.
- The bright yellow zone is not the hottest — the outer blue zone is.
- PVC = polyvinyl chloride, not carbonate.
- Aspartame is a sweetener, not a preservative.
CHECK YOURSELF
Why does a paper cup full of water not catch fire over a candle?
Show answer
The heat passes from the paper into the water, so the paper never reaches its ignition temperature. The water warms; the cup does not burn.
FLASHCARDS
Fuels and materials flashcards
- Unrefined petroleum
- Crude oil (black gold)
- Cooking gas (LPG)
- Butane + propane
- Marsh gas
- Methane, CH4
- Cause of mine explosions
- Methane + air
- Hottest flame zone
- Outermost, blue
- PVC
- Polyvinyl chloride
- Aspartame
- Artificial sweetener
- Concrete, fibreglass
- Composite materials
QUICK BYTES
- Coal products: coke, coal tar, coal gas
- Petroleum = crude oil = black gold
- CNG methane, from gas wells; burns cleanly
- Fire needs fuel, air, heat; CO2 for oil and electrical fires
- Highest calorific value: hydrogen, 150,000 kJ/kg
- Rayon artificial silk; acrylic artificial wool; nylon fully synthetic
- Thermosetting: bakelite, melamine; thermoplastic: polythene, PVC