NCERT Solutions For Class 8 Science Chapter 5
Coal and Petroleum

Bitumen is used for surfacing of roads.

1. About 300 million years ago the earth had dense forest in low lying wetlands. Due to natural processes like flooding and earthquakes, forests got buried under the soil. With the passage of time, as more and more soil got deposited on them, the buried plants were compressed. Deep down the earth, pressure and temperature was very high. Under high pressure and temperature, slowly plants got converted into coal.
2. The slow process of conversion of dead vegetation into coal is called carbonisation.

The amount of fossil fuels available in nature is limited. The formation of fossil fuels takes millions of years. Fossil fuels are made by the action of heat and pressure on the remains of dead vegetation and animals. The rate at which we are using them is very fast as compared to their rate of formation. Therefore, fossil fuels are exhaustible natural resources.

1. coal, petroleum, natural gas
2. refining
3. CNG

• Petroleum originated from the remains of sea organisms.
• When sea organisms died, they got buried at the bottom of sea.
• With passage of time, their bodies got covered with mud.
• Pressure and temperature rose as they got buried lower and lower.
• Due to the effect of heat, pressure and action of bacteria in the absence of air, the buried remains decomposed very slowly forming petroleum.

Coke is a black porous substance. It is obtained as residue during destructive distillation of coal. The characteristics of coke are as follows:

1. Coke is an almost pure form of carbon.
2. It burns almost with no smoke.
3. It is a non-conductor of heat and electricity.

Uses of coke are as follows:

1. Coke is used in the extraction of metals.
2. It is also used in the manufacturing of steel.

1. Fossil fuels can be made in the laboratory.   (F)
2. CNG is more polluting fuel than petrol.         (F)
3. Coke is almost pure form of carbon.             (T)
4. Coal tar is a mixture of various substances.  (T)
5. Kerosene is not a fossil fuel.                        (F)

The advantages of using LPG as a fuel are as follows:

1. LPG burns easily with smokeless flame. It is a clean fuel.
2. LPG has high calorific value.
3. LPG does not produce any poisonous gases on burning.
4. LPG does not leave behind any solid residue on burning.

The advantages of using CNG as a fuel are as follows:

1. CNG burns easily with smokeless flame. It is a clean fuel.
2. CNG can be used directly for burning in homes and factories.
3. CNG is used as a fuel for vehicles because it is less polluting.
4. CNG is used as a fuel in thermal power stations for generating electricity.