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

The advantages of using Compressed Natural Gas (CNG) and Liquefied Petroleum Gas (LPG) as fuels include:

• Reduced Pollution: They are considered cleaner fuels compared to petrol and diesel, making them suitable for use in transport vehicles and reducing air pollution.
• Ease of Storage and Transport: Both CNG and LPG are relatively easy to store and transport, often through pipelines or in specialized cylinders.
• Versatile Use: CNG can be used for power generation, while LPG is commonly used for cooking in homes and for industrial heating.
• High Energy Content: These fuels possess a higher energy content per unit volume, meaning they can provide more energy for the same amount of fuel.
• Clean Burning: LPG and CNG burn with very few or virtually no ash particles left behind, contributing to cleaner combustion.
• Availability and Affordability: They are generally readily available and often more affordable than other fuel options.

The petroleum product commonly used for surfacing roads is Bitumen. It is a residue obtained from the refining of petroleum and is known for its adhesive properties, making it ideal for binding road materials.

Coal formation is a process that began approximately 300 million years ago when the Earth had dense forests, particularly in low-lying wetland areas. The process occurred as follows:

1. Burial: Due to natural events like floods, the vegetation from these forests got buried under layers of soil and sediment.
2. Compression: As more soil and rock accumulated over millions of years, the buried vegetation was subjected to immense pressure.
3. Heating: Simultaneously, the increasing depth of burial led to a rise in temperature.
4. Conversion: Under the combined effects of high pressure and high temperature over vast periods, the dead plant matter underwent a slow chemical transformation.

This slow process of conversion of dead vegetation into coal is called carbonisation. Since coal is predominantly composed of carbon, the term reflects this transformation.

1. Fossil fuels are Natural Gas, Coal and Petroleum.
2. The process of separation of different constituents from petroleum is called refining. This process separates crude oil into various useful fractions like petrol, diesel, kerosene, etc.
3. The least polluting fuel for vehicles is CNG (Compressed Natural Gas).

(a) Fossil fuels can be made in the laboratory. (False) - Fossil fuels take millions of years to form under specific geological conditions that cannot be replicated quickly in a lab.

(b) CNG is more polluting fuel than petrol. (False) - CNG is a cleaner fuel and produces significantly less pollution than petrol.

(c) Coke is almost pure form of carbon. (True) - Coke is a solid carbon material derived from coal, and it is nearly pure carbon.

(d) Coal tar is a mixture of various substances. (True) - Coal tar is a complex mixture containing hundreds of different chemical compounds, including benzene, toluene, and xylene.

(e) Kerosene is not a fossil fuel. (False) - Kerosene is a refined product of petroleum, which is a fossil fuel.

Fossil fuels are considered exhaustible natural resources because their formation process is extremely slow, taking millions of years. They are formed from the decomposed remains of ancient plants and animals under conditions of high temperature and pressure deep within the Earth.

While these resources are finite and exist in limited quantities, human activities are consuming them at a rate far exceeding their natural rate of formation. If we continue to deplete them at the current pace, they will eventually run out. Therefore, they are classified as exhaustible – meaning they can be used up.