Samacheer Class 8 Science - Chemistry in Everyday Life

Natural gas has numerous advantages that make it a valuable energy resource. It produces a lot of heat as it is easily burnt, making it an efficient fuel for generating energy. It does not leave any residue after combustion, which means there is no ash or solid waste to dispose of. Natural gas burns without smoke and therefore causes no air pollution, making it an environmentally friendly fuel compared to coal and other fossil fuels. This can be easily supplied through pipes to homes and industries, making distribution convenient and safe. It can be directly used as fuel in homes for cooking and heating, and in industries for various manufacturing processes. Natural gas is also a cleaner-burning fuel that produces fewer greenhouse gases compared to coal and oil, making it a more sustainable energy option for the future.

CNG stands for Compressed Natural Gas. It is one of the cheapest and cleanest fuels available for use in vehicles and industrial applications. CNG is primarily used as a fuel for automobiles, buses, and trucks, offering significant environmental and economic advantages. Vehicles powered by CNG produce considerably less carbon dioxide and hydrocarbon emissions compared to those running on petrol or diesel, making it an environmentally friendly choice. CNG is also less expensive than both petrol and diesel, which makes it economically attractive for consumers. Additionally, CNG can be used in power generation plants and as a fuel for cooking in households. Its lower pollution levels and reduced greenhouse gas emissions make it a preferred alternative fuel in urban areas where air quality is a concern. The widespread adoption of CNG-powered vehicles has helped reduce urban air pollution significantly in many cities.

Water gas is also known as syngas or synthesis gas. It is called syngas because of its primary industrial application as a synthesis gas, which means it is used to synthesize or produce other useful chemical compounds. Specifically, water gas is used to synthesize methanol and simple hydrocarbons through chemical reactions. Beyond its role in chemical synthesis, water gas also serves as an important industrial fuel in various manufacturing processes. The term synthesis gas reflects its versatility and importance in converting it into more complex and useful chemical products rather than being used directly as a fuel. This makes water gas a valuable intermediate product in the chemical and petrochemical industries.

Anthracite is recognized as the highest grade of coal due to several distinctive characteristics that make it superior to other coal types. Anthracite has the highest carbon content among all coal varieties, containing between 86 and 97 percent carbon, which directly contributes to its exceptional energy output. It is an extremely hard coal with a deep black color and a shiny appearance, making it easily distinguishable from lower grades of coal. The heating value of anthracite is slightly higher than bituminous coal, meaning it releases more energy when burned. When anthracite burns, it produces significantly more heat and burns for a longer duration compared to other coal types, making it highly efficient as a fuel. Additionally, anthracite produces very little dust during combustion and handling, which reduces air pollution and makes it cleaner to use. These combined properties of high carbon content, superior heat output, longer burning time, and minimal dust production establish anthracite as the most valuable and highest quality coal available.

Octane number and cetane number are two different rating systems used to measure the quality and performance characteristics of different fuels. Octane number is a rating system specifically used for petrol or gasoline. It measures the amount of octane present in petrol and indicates the fuel's ability to resist knocking or detonation in petrol engines. The octane number of petrol can be increased by adding aromatic hydrocarbons such as benzene or toluene. Fuels with high octane numbers are more resistant to premature ignition and provide better engine performance. Cetane number, on the other hand, is a rating system used exclusively for diesel fuel. It measures the ignition delay of the fuel in a diesel engine, indicating how quickly the fuel ignites when injected into the engine. The cetane number of diesel can be increased by adding additives such as acetone. Fuels with high cetane numbers ignite more readily and provide better combustion characteristics in diesel engines. An important distinction is that fuels with high octane numbers typically have low cetane numbers, and vice versa, as these properties are inversely related. This inverse relationship reflects the different combustion requirements of petrol and diesel engines.

Solar energy is justifiably considered a non-depleting energy source for several compelling reasons. The sun provides a free and renewable source of energy that will continue to be available for billions of years, making it essentially inexhaustible on human timescales. Unlike fossil fuels such as coal, petroleum, and natural gas, which are finite resources that deplete with use, solar energy is continuously replenished by the sun's radiation. Solar energy is a renewable type of energy that does not endanger or harm the environment, as it produces no greenhouse gases or air pollutants during its conversion to usable forms. It represents a potential and viable source to replace fossil fuels in order to meet the energy needs of the world's growing population. With continuous advancements in science and technology, solar energy has become increasingly affordable and accessible, with improvements in photovoltaic cell efficiency and solar panel manufacturing. The decreasing costs and increasing efficiency of solar technology make it economically competitive with traditional energy sources. Solar energy can effectively overcome the global energy crisis by providing a sustainable, clean, and abundant alternative to fossil fuels. As solar technology continues to improve, it offers a promising solution for meeting future energy demands while protecting the environment for future generations.

Lignite:
Lignite is a brown coloured coal of lowest grade.
It has least content of carbon. The carbon content of lignite is 25 – 35%.
Lignite contains a high amount of water and makes up almost half of our total coal reserves.
It is used for electricity generation.
It is used to generate synthetic natural gas and produce fertilizer products.
Sub-bituminous:
When lignite becomes darker and harder over time, sub-bituminous coal is formed.
Sub-bituminous coal is a black and dull coal.
It has higher heating value than lignite and contains 35-44% carbon.
It is used primarily as fuel for electricity power generation.
This coal has lower sulfur content than other types and bums cleaner.
Bituminous:
With more chemical and physical changes, sub-bituminous coal is developed into bituminous coal.
It is dark and hard. It contains 45-86% carbon. It has high heating value.
It is used to generate electricity.
Other important use of this coal is to provide coke to iron and steel industries.
By-products of this coal can be converted into different chemicals which are used to make paint, nylon and many other items.
Anthracite:
It is the highest grade coal. It is hard and dark black in colour.
It has a very light weight and the highest heat content.
Anthracite coal is very hard, deep black and shiny.
It contains 86-97% carbon and has a heating value slightly higher than bituminous coal.
It bums longer with more heat and less dust.

Destructive distillation is the process of heating coal in the absence of air or oxygen. When coal is heated in the absence of air, it does not burn but instead undergoes a chemical decomposition that produces many valuable by-products. This process is called destructive distillation of coal because the coal structure is broken down or destroyed through heating without combustion, yielding useful products. Petroleum is a complex mixture of hydrocarbons that undergoes fractional distillation to separate it into various useful products based on their boiling points. The products obtained from petroleum include liquefied petroleum gas or LPG, which is used as a fuel for cooking and heating. Petrol and diesel are obtained as middle fractions and are used as fuels for vehicles. Kerosene is obtained and used as a fuel for lamps and heating. Lubricating oil is extracted and used to reduce friction in machinery and engines. Paraffin wax is obtained and used in candles and polishes. Bitumen or asphalt is a heavy fraction used in road construction and waterproofing. Refinery gas is produced during the distillation process and used as a fuel. Naphtha is obtained and used as a raw material in the chemical industry. Fuel oil is used in power plants and heating systems. Various chemicals are extracted for use in pharmaceuticals and other industries. Jet fuel is produced for aircraft propulsion. Waxes are obtained for use in cosmetics and polishes. These diverse products demonstrate the importance of petroleum as a valuable resource for modern society.

Fuels are classified into solid, liquid and gaseous fuels according to their physical state.
Solid fuels:
Fuels like wood and coal are in solid state and they are called solid fuels.
This type of fuel was the first one to be used by man.
These fuels are easy to store and transport.
The production cost is also very low.
Liquid fuels:
Most of the liquid fuels are derived from the fossil remains of dead plants and animals petroleum oil, coal tar and alcohol are some of the liquid fuels.
These fuels give more energy on burning and bum without ash.
Gaseous fuel:
Coal gas, oil gas, producer gas and hydrogen are some of the gaseous fuels.
It can be easily transported through pipes and they do not produce pollution.