CBSE Class 8 Science Chapter 5: Coal and Petroleum NCERT Solutions

Compressed Natural Gas (CNG) and Liquefied Petroleum Gas (LPG) offer several advantages as fuels:

• Reduced Pollution: They are considered cleaner fuels compared to traditional options like petrol and diesel, making them ideal for use in vehicles and reducing air pollution.
• Ease of Storage and Transport: Both CNG and LPG are relatively easy to store and transport, facilitating their widespread use.
• Versatile Applications: CNG is increasingly used for power generation, while LPG can be directly used for cooking and heating in homes and industrial processes.
• High Energy Content: They possess a higher energy content per unit volume than many other fuels.
• Clean Burning: When burned, CNG and LPG leave behind virtually no ash particles, contributing to cleaner combustion.
• Affordability and Availability: These fuels are generally available and affordable, making them accessible for various applications.

The petroleum product primarily used for surfacing roads is Bitumen. It is a thick, black, and sticky substance obtained during the refining of petroleum.

The formation of coal is a lengthy geological process that began approximately 300 million years ago. At that time, the Earth had dense forests, particularly in low-lying wetland areas. Due to natural events like floods, these forests were buried under layers of soil and sediment.

As more soil accumulated, the buried vegetation was subjected to increasing pressure and temperature. Under these high-pressure and high-temperature conditions, the dead plant matter underwent a slow chemical and physical transformation. This process gradually converted the dead vegetation into coal.

The slow process of conversion of dead vegetation into coal, which is primarily composed of carbon, is known as carbonisation.

1. Fossil fuels are Coal, Petroleum and Natural Gas.
2. The process of separation of different constituents from petroleum is called refining.
3. The least polluting fuel for vehicles is CNG (Compressed Natural Gas).

1. Fossil fuels can be made in the laboratory. (False) - Fossil fuels take millions of years to form under specific geological conditions and cannot be practically synthesized in a laboratory setting.
2. CNG is more polluting fuel than petrol. (False) - CNG is generally considered a cleaner fuel than petrol, producing fewer harmful emissions.
3. Coke is almost pure form of carbon. (True) - Coke is a solid carbon material produced from coal and is almost pure carbon.
4. Coal tar is a mixture of various substances. (True) - Coal tar is a complex by-product of coal processing, containing hundreds of different chemical compounds.
5. Kerosene is not a fossil fuel. (False) - Kerosene is a petroleum product, and petroleum is a fossil fuel formed from ancient organic matter.

Fossil fuels are classified as exhaustible natural resources because their formation process is extremely slow, taking millions of years. They are created from the remains of dead plants and animals that were subjected to intense heat and pressure deep within the Earth over geological timescales.

While humans consume these fuels at a rapid pace for energy, their natural replenishment rate is incredibly slow. If we continue to deplete these resources at the current rate, they will eventually run out. Unlike resources that can be regenerated quickly (like solar or wind energy), fossil fuels cannot be recreated in a short period, making them finite and exhaustible.