The concept of thermodynamics is a key aspect of Chemistry Topics as it deals with the study of energy transformations in chemical systems and the relationships between energy, heat, and work.
What Are Natural Resources ? How Coal can be used as a Fossil Fuel ?
In our everyday life, we use a large number of materials for our basic needs. Some of these materials are found in nature whereas others are man-made. Air, water, soil, sunlight, coal, petroleum, natural gas and minerals are obtained from nature, so they are called natural resources. On the other hand, plastics, synthetic fibres, paints, drugs, explosives, etc., are all man-made materials.
Inexhaustible and Exhaustible Natural Resources
Anything in the environment ‘which can be used’ is called a ‘resource All the natural resources can be classified into two main groups :
- Inexhaustible natural resources, and
- Exhaustible natural resources.
The term ‘inexhaustible’ means something ‘which cannot be used up completely Those natural resources which arc present in unlimited quantity in nature and are not likely to be exhausted by human activities are called inexhaustible natural resources.
The examples of inexhaustible natural resources are : Sunlight, Air and Water. There is a never ending supply of inexhaustible resources in nature. The inexhaustible resources can be used again and again. They last forever. The term ‘exhaustible’ means ‘something which can be used up completely’ (so that nothing is left behind).
Those resources which are present in a limited quantity in nature and can be exhausted by human activities, are called exhaustible natural resources. The examples of exhaustible natural resources are : Coal, Petroleum, Natural gas, Minerals, Forests and Wildlife, etc. The exhaustible natural resources do not last forever.
In this Chapter we will study some exhaustible sources of energy like coal, petroleum and natural gas. Coal, petroleum and natural gas are also called non-renewable sources of energy. This is because when all the coal, petroleum and natural gas present under the earth will get used up (or exhausted), no more supply of these fuels will be available in the near future. Before we go further, we should know the meaning of the term ‘fossil’. Fossils are the remains of the pre-historic plants or animals, buried under the earth millions of years ago.
Fossil Fuels
The natural fuels formed from the remains of living organisms buried under the earth long, long ago, are called fossil fuels. Coal, petroleum and natural gas are fossil fuels. Coal, petroleum and natural gas are called fossil fuels because they were formed by the decomposition of the remains of pre-historic plants and animals (fossils) buried under the earth long, long ago.
Fossil fuels are exhaustible natural resources because once all the fossil fuels are used up, they will be gone forever.
How Fossil Fuels were Formed
Fossil fuels were formed from the dead remains of living organisms (plants and animals) buried under the earth millions of years ago. This happened as follows : 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 air.
In the absence of air, the chemical effects of heat, pressure and bacteria, converted the buried remains of plants and animals into fossil fuels like coal, petroleum and natural gas. Please note that the buried remains of large land plants were converted into coal whereas those of tiny marine plants and animals were converted into petroleum and natural gas.
Coal
Coal is a hard, black combustible mineral that consists mainly of carbon (see Figure). Coal is found in deep coal mines under the surface of the earth. In India, coal is found mainly in Bihar, West Bengal, Orissa and Madhya Pradesh.
Coal is found in abundance in our country and it is the most important source of energy in our country.
How Coal was Formed
Coal was formed by the decomposition of large land plants and trees buried under the earth about 300 million years ago. This happened as follows: About 300 million years ago, the earth had dense forests in low- lying wet land areas. Due to natural processes like earthquakes, volcanoes and floods, etc., these forests were buried under the surface of earth.
As more soil deposited over them, they were compressed. The temperature also rose as they sank deeper and deeper. Due to high pressure and high temperature inside the earth, and in the absence of air, the wood of buried forest plants and trees was slowly converted into coal.
The slow process by which the dead plants buried deep under the earth have become coal is called carbonisation. Since coal was formed from the remains of plants, therefore, coal is called a fossil fuel.
Coal is a Source of Energy
Coal is mainly carbon. When heated in air, coal burns and produces mainly carbon dioxide gas. A lot of heat energy is also produced during the burning of coal. This can be written as :
Coal is important because it can be used as a source of heat energy as such (just by burning it), or it can be converted into other forms of energy such as coal gas, coke or electricity.
The real source of energy of coal is the solar energy (or sun’s energy). This is because the plants and trees which decomposed to form coal grew on the earth by absorbing sunlight energy during the process of photosynthesis.
Uses of Coal
- Coal is used as a fuel in homes and industry.
- Coal is used as a fuel at Thermal Power Plants for generating electricity.
- Coal is used to make coal gas which is an important industrial fuel.
- Coal is used to make coke.
- Earlier, coal was used as a fuel to make ‘steam’ to run steam engines of trains.
- Coal was also used as a source of organic chemicals.
Products of Coal
When coal is heated strongly in closed retorts in the absence of air, a number of useful products are obtained. The various useful products obtained by processing the coal by heating in the absence of air are:
- Coal gas,
- Coal tar, and
- Coke.
Coal gas, coal tar and coke are called products of coal. Please note that these products are obtained when coal is heated in the absence of air. This is because if coal is heated in the presence of air, then coal burns to produce mainly carbon dioxide gas and no other useful products are obtained.
The strong heating of coal in the absence of air is called destructive distillation of coal. We will now describe the various products of coal in somewhat detail.
Coal Gas
Coal gas is a gaseous fuel which is obtained by the strong heating of coal in the absence of air during the processing of coal to get coke. Coal gas is mainly a mixture of methane and hydrogen, with some carbon monoxide. All the gases present in coal gas can burn to produce heat, due to which coal gas is an excellent fuel (having high calorific value).
Coal gas is used as a fuel in industries (which are situated near the coal processing plants). When coal gas burns, it also produces a good amount of light. So, in the past, coal gas has also been used for lighting purposes (or illumination purposes). Coal gas was used for street lighting for the first time in London in the year 1810. It was used for street lighting in New York around 1820. These days, however, coal gas is used as a source of heat rather than light.
Coal Tar
Coal tar is a thick, black liquid having an unpleasant smell which is obtained by heating coal in the absence of air (see Figure). Coal tar is not a single compound. Coal tar is a mixture of about 200 carbon compounds (or organic compounds). The useful carbon compounds (or organic compounds) present in coal tar include benzene, toluene, naphthalene, anthracene, phenol and aniline.
Thus, the naphthalene balls used to repel moths and other insects (in stored clothes, etc.) are obtained from coal tar. The various compounds present in coal tar are separated by the process of fractional distillation. The compounds (or products) obtained from coal tar are used as starting materials for manufacturing a large number of substances used in everyday life and industry.
For example, the products of coal tar are used to make synthetic fibres, drugs (medicines), plastics, synthetic dyes, perfumes, paints, varnishes, pesticides, photographic materials, roofing materials and explosives, etc. Coal tar has been traditionally used for metalling the roads. These days, however, bitumen (a petroleum product) is being used increasingly for metalling the road surfaces (in place of coal tar).
Coke
Coke is a tough and porous black solid substance (see Figure). Coke is prepared by heating coal in the absence of air. When coal is heated in the absence of air, then coal gas and coal tar are eliminated, and coke is left behind as a black residue. Thus, coal minus volatile constituents is coke. Coke is an almost pure form of carbon. It is 98 per cent carbon.
Coke is mainly used as a reducing agent in the extraction of metals (like iron, zinc, etc.) Coke is used in the manufacture of steel. Coke is also used as a fuel. Coke is a better fuel than coal because it produces more heat on burning than an equal amount of coal. Moreover, coke burns without producing any smoke whereas coal produces a lot of smoke on burning.