Fossil Fuels

By | December 3, 2018

Question 1 What are fossil fuels?Give examples of fossil fuels?

Question 2 How fossil fuels were formed?

Question 3 How Sun is considered as ultimate source of fossil fuels?

Question 4 How coal is formed?

Question 5 How petroleum is formed?

Question 6 Why LPG is considered a better fuel than coal?

Question 7 What is meant by conventional sources of energy?

Question 8 What are the disadvantages of burning fossil fuels?

Question 9 What precautions should be taken if LPG leakage is detected in kitchen?

Question 10 What is the composition of LPG?

Question 11 State few uses of coal?

Question 12 Why coke is a better fuel than coal?

Conventional Sources of Energy

The traditional sources of energy which are familiar to most people are called conventional sources of energy. The main conventional sources of energy are wood and fossil fuels (like coal, petroleum and natural gas). The fuels derived from wood, coal and petroleum such as charcoal, coke, coal gas, petrol, diesel, kerosene, fuel oil and liquefied petroleum gas (LPG) are also known as conventional sources of energy (or conventional fuels).

Fossil Fuels

A natural fuel formed deep under the earth from the pre-historic remains of living organisms (like plants and animals) is called a fossil fuel. Coal, petroleum and natural gas are fossil fuels. Fossil fuels are dug out from the earth. Besides being used directly in homes, transport vehicles and industry, fossil fuels are the major source of energy for generating electricity in power plants.

Formation Of Fossil Fuels

The plants and animals which died millions of years ago, were gradually buried deep in the earth and got covered with sediments like mud and sand, away from the reach of oxygen of air. In the absence of oxygen, the chemical effects of pressure, heat and bacteria, converted the buried remains of plants and animals into fossil fuels like coal, petroleum and natural gas. The buried remains of large plants were converted into coal whereas those of small plants and animals were converted into petroleum and natural gas.

Sun is the Ultimate Source of Fossil Fuels

Fossil fuels have been produced from the remains of plants and animals that were buried in the earth long ago. It was the sunlight of long ago that made plants grow, which were then converted into fossil fuels.The green plants need sunlight energy to grow. They get this energy from sunlight, and store it in the form of carbon compounds. So, every leaf and every bit of wood in the plant was made with the energy of sunlight. The animals also eat plants, so the animal material is also a store-house of sun’s energy. These plants and animals which were originally made by using sun’s energy have been converted into fossil fuels like coal, petroleum and natural gas. Thus, fossil fuels are energy-rich compounds of carbon which were originally made by the plants with the help of sun’s energy (solar energy). Without sunlight, there could have been no coal, petroleum, natural gas, wood or any other fuel in this world.


Coal is a complex mixture of compounds of carbon, hydrogen and oxygen, and some free carbon.Small amounts of nitrogen and sulphur compounds are also present in coal.

When coal is burnt, the carbon present in coal reacts with the oxygen of air to form carbon dioxide. A lot of heat is produced during the burning of coal which makes it a good fuel. The burning of coal produces a lot of smoke which pollutes the air.When coal is subjected to destructive distillation (by strongly heating in the absence of air), then all the volatile material is removed from coal and coke is formed.

Coke is a better fuel than coal because it produces more heat (than an equal mass of coal), and it does not produce smoke while burning. Thus, burning of coke does not cause air pollution.Coke is, however, more valuable when used as a reducing agent in the extraction of metals from their ores.

Uses of Coal

(1) Coal is used as a fuel for heating purposes in homes and in industry.

(2) Coal is used as a fuel in thermal power plants for generating electricity.

(3) Coal is used to make coke. And this coke is then used as a reducing agent in the extraction of metals.

(4) Coal is used in the manufacture of fuel gases like coal gas.

(5) Coal is used in the manufacture of petrol and synthetic natural gas.


Petroleum is a dark coloured, viscous, and foul smelling crude oil. It is called petroleum because it is found under the crust of earth trapped in rocks. The crude oil petroleum is a complex mixture of several solid, liquid and gaseous hydrocarbons mixed with water, salt and earth particles. Petroleum is lighter than water and insoluble in it.

Petroleum occurs deep down under the earth between two layers of impervious rocks (non-porous rocks). Natural gas occurs above the petroleum oil trapped under the rocks. Petroleum is obtained by drilling holes (called oil wells) into the earth’s crust where the presence or oil has been predicted by survey. When a well is drilled through the rocks, natural gas comes out first with a great pressure and for a time, the crude oil comes out by itself due to gas pressure. After the pressure has subsided, the crude oil is pumped out of the oil well.

Before petroleum can be used as a fuel for specific purposes, it has to be purified or refined by the process of fractional distillation.

The fractional distillation of petroleum gives us the following fractions which can be used as fuels: Petroleum gas, Petrol (or Gasoline), Diesel, Kerosene and Fuel oil.

Petroleum gas is used as a fuel for domestic heating purposes in the form of liquefied petroleum gas (LPG).

Petrol is used as a fuel in motor cars, scooters, motor-cycles, and other light vehicles.

Diesel is used as a fuel for heavy vehicles like buses, trucks, tractors, and railway engines. Diesel is also used as a fuel to run water-pumps for irrigation purposes, and in diesel generators to produce electricity on a small scale. 

Kerosene oil is used as a household fuel. For example, kerosene is used in wick stoves or pressure stoves to cook food. Kerosene is also used as an illuminant (for lighting purposes) in hurricane lamps. A special grade of kerosene oil is used as aviation fuel in jet aeroplanes.

Fuel oil is used in industries to heat boilers and in furnaces. Fuel oil is also used in thermal power plants for generating electricity. Fuel oil is a better fuel than coal because fuel oil burns completely and does not leave any residue.

Petroleum Gas

The main constituent of petroleum gas is butane though it also contains smaller amounts of propane and ethane. Petroleum gas is a mixture of three hydrocarbons: butane, propane and ethane. Butane, propane and ethane, all burn readily, producing a lot of heat. This makes petroleum gas a very good fuel.

Petroleum gas is obtained as a by-product in oil refineries from the fractional distillation of petroleum. If is also produced by the cracking of petrol. 

The petroleum gas which has been liquefied under pressure is called Liquefied Petroleum Gas (LPG) . Thus, liquefied petroleum gas (or LPG) consists mainly of butane (along with smaller amounts of propane and ethane) which has been liquefied by applying pressure.

The domestic gas cylinders like Indane contain mainly butane, with smaller amounts of propane and ethane, under pressure.

Petroleum gas is supplied in liquid form so that even a small cylinder may contain a good weight of the gas. A domestic gas cylinder contains about 14 kilograms of LPG. A strong smelling substance called ethyl mercaptan (C2H5SH) is added to LPG cylinders to help in the detection of gas leakage. Ethyl mercaptan has a foul smell resembling that of hydrogen sulphide gas which can be easily detected.The gas used for domestic cooking is called Liquefied Petroleum Gas (LPG) because it is obtained from petroleum and it is liquefied by compression before filling into the cylinders.

When we turn on the knob of the gas cylinder, the pressure is released and the highly volatile LPG gets converted into gas. This gas goes into the burner of our cooking stove. When a burning matchstick is applied to the burner, the gas burns with a blue flame producing a lot of heat. This heat is used for cooking food.

Advantages of LPG

(1) LPG has a high calorific value. So, it is a good fuel. The calorific value of LPG is about 50 kJ/g That is, when 1 gram of LPG burns in a gas stove, it produces 50 kilojoules of heat energy.

(2) LPG burns with a smokeless flame and so does not cause air pollution.

(3) LPG does not produce any poisonous gases on burning.

(4)LPG is easy to handle and convenient to store

(5) LPG is a very neat and clean domestic fuel.

Dangers of LPG

LPG is a highly inflammable gas, that is, it catches fire easily. Any leakage of LPG from the gas cylinder, stove or the rubber pipe (connecting the cylinder and stove) will form an explosive mixture with air in the kitchen.

Precautions for Using LPG

(1) Before lighting a matchstick we should make sure that there is no foul smell of the leaking gas in the kitchen, near the gas cylinder or gas stove. If we smell gas leakage on entering the kitchen, then the door and windows should be opened at once to allow the gas to escape. We should never light a matchstick or a candle during the leakage of LPG in the kitchen.

(2) We should not use any hot flames like a kerosene lamp, kerosene stove or electric heater near the gas cylinder.

(3) We should never use a leaking gas cylinder. The Gas Agency should be informed and the leaking gas cylinder replaced at the earliest.

(4) We should handle the gas cylinder with care so that its valve does not get damaged.

(5) The rubber pipe connecting the gas cylinder to gas stove should be checked periodically for any wear and tear.

(6) In order to light the gas stove, we should first open the valve of the cylinder and then turn on the knob of gas stove.

(7) In order to put off the gas stove, we should first close the valve of the cylinder and after that the knob of the gas stove should be turned off.

(8) When the gas is not being used, the valve of the gas cylinder and the knobs of the gas stove must be kept closed.

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