Coal and Petroleum - Class 8 Notes & Olympiad Questions

Coal and Petroleum - Class 8 Science

  • Natural Resources
  • Fuel
  • Fossil Fuels
  • Coal
  • Petroleum
  • Natural Gas
  • Solved Questions on Coal and Petroleum
  • Natural Resources

    Natural resources are valuable assets that we obtain from the Earth and the environment around us. These resources play a crucial role in supporting human life and powering our economies. Natural resources can be broadly classified into two main types:

    1. Inexhaustible Natural Resources

    Inexhaustible natural resources are those that are present in nature in unlimited quantities and cannot be depleted, no matter how much we use them. These resources are essentially limitless and will always be available to us. Examples of inexhaustible natural resources include:

    a) Sunlight: The energy from the sun that provides us with light and heat.
    b) Wind: The movement of air that can be harnessed to generate wind energy.
    c) Water: The vast bodies of water on Earth, such as oceans and rivers, which can be used for various purposes like drinking, irrigation, and generating hydroelectric power.

    2. Exhaustible Natural Resources

    Exhaustible natural resources are those that are present in limited quantities and can be depleted over time if we use them excessively. These resources are not infinite, and their availability may decrease with continued usage. Examples of exhaustible natural resources include:

    a) Fossil Fuels: Fossil fuels like coal, petroleum, and natural gas, are formed from ancient plants and animals over millions of years. These fuels are used for energy production, transportation, and various industrial processes.
    b) Forests: The vast areas covered with trees that provide us with wood, oxygen, and habitats for numerous plants and animals. Deforestation and excessive logging can deplete forests.
    c) Minerals: Valuable minerals found in the Earth's crust, such as iron, copper, and gold, which are essential for various industries like construction, electronics, and manufacturing.


    a) Fuel is a substance that provides energy when burned. It is like the food that powers machines, vehicles, and various devices we use in our everyday lives. Just as we need food to stay active and energized, machines and vehicles need fuel to function and do their jobs.
    b) When we burn fuel, a chemical reaction takes place, releasing energy in the form of heat and light. This energy is used to power engines in vehicles, generate electricity in power plants, and provide heat for cooking and heating.
    c) There are different types of fuels, and they can be classified based on their physical states: solid, liquid, or gas.

    Some common examples of fuels include:

    a) Solid Fuels: These are fuels that are in a solid state at room temperature. Examples include wood, charcoal, and coal. In the past, people used wood and charcoal to cook food and heat their homes. Coal is a fossil fuel that was widely used in steam engines and power plants in the past.

    b) Liquid Fuels: These are fuels that are in a liquid state at room temperature. Examples include petrol (gasoline), diesel, and kerosene. Liquid fuels are commonly used in vehicles like cars, trucks, and aeroplanes to make them move.

    c) Gas Fuels: These are fuels that are in a gaseous state at room temperature. Examples include natural gas and propane. Gas fuels are used for cooking, heating, and generating electricity.

    Flowchart of Classification of Fuels - Science Grade 8

    Characteristics of a Good Fuel

    The characteristics of good fuel are important to understand because they determine how efficient and beneficial a fuel is for various applications. Here are the main characteristics of a good fuel:

    1. High Calorific Value: The first characteristic is a high calorific value, which means the fuel can produce a lot of energy when burned.
    Calorific value, also known as energy value or heating value, is a measure of the energy content stored in a specific amount of a substance, typically food or fuel. It indicates the amount of heat released when the substance is burned or metabolized.
    Fuels with high calorific values can provide more heat and power for a longer time, making them more efficient.

    2. Economical: A good fuel should be economical, which means it should be affordable and easily accessible. When a fuel is economical, it can be used by many people and industries without putting a strain on their budgets.

    3. Easy to Handle and Transport: Fuels should be easy to handle and transport. For example, liquid fuels like petrol and diesel should flow smoothly through pipes, and solid fuels like coal and wood should be easy to store and carry.

    4. Low Ignition Temperature: The ignition temperature is the temperature at which a fuel starts burning. A good fuel should have a low ignition temperature, so it can start burning easily when exposed to a spark or heat source.

    5. Environmentally Friendly: Ideally, a good fuel should be environmentally friendly, meaning it should produce minimal pollution and harmful gases when burned. Fuels that cause less pollution are better for the environment and help combat issues like air pollution and climate change.

    6. Low Ash Content: For solid fuels like coal, a low ash content is desirable. Ash is the residue left behind after burning, and if the ash content is low, it means less waste is produced during combustion.

    By considering these characteristics, we can make informed choices about the types of fuels we use for different purposes. For example, in vehicles, we often use petrol and diesel because they have high calorific values and are easy to handle. On the other hand, for generating electricity, we are increasingly shifting towards renewable sources like solar and wind energy, which are more environmentally friendly and sustainable in the long run. Understanding these characteristics helps us use fuels more efficiently and responsibly for a cleaner and greener future.

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    Fossil Fuels

    Fossil fuels are a type of natural resource that provides us with a major source of energy. They are called "fossil fuels" because they are formed from the remains of ancient plants and animals that lived millions of years ago. These plants and animals died and were buried under layers of earth and sediment.

    Over millions of years, the dead plants and animals underwent a process called "fossilization." The heat and pressure from the layers of earth and sediment transformed their remains into fossil fuels. The three main types of fossil fuels are coal, oil (also known as petroleum), and natural gas.


    a) Coal is a type of fossil fuel, and it's an essential source of energy that has been used by humans for a very long time.
    b) Coal is a hard and black-coloured rock-like substance that we find deep underground. It's formed from the remains of ancient plants that lived on Earth millions of years ago.
    c) These plants grew in swamps and wetlands. When these plants died, they fell into the water and accumulated at the bottom of the swamps.

    Formation of Coal

    Over millions of years, these dead plants got buried under layers of mud, sand, and other materials. The weight of these layers, along with the heat and pressure from the Earth's crust, caused the dead plants to undergo a transformation. They slowly turned into coal through a process called "carbonization." During carbonization, the plant material goes through chemical changes and loses moisture, leaving behind coal.

    Diagram of Formation of Coal - Science Grade 8

    Different Types of Coal

    There are different types of coal based on their carbon content and properties. The main types of coal are:

    a) Peat: This is the earliest stage of coal formation. It has a lot of moisture and is not fully transformed into coal yet.

    b) Lignite: Also known as "brown coal," it has more carbon than peat and is a bit harder.

    c) Bituminous Coal: This is a type of coal that has even more carbon and is commonly used for producing electricity.

    d) Anthracite: This is the highest grade of coal, with the most carbon content and the hardest form.

    Flow Chart of Different Types of Coal - Science Grade 8

    Diagram of Different Types of Coal - Science Grade 8

    Usage of Coal

    Coal has been used for various purposes throughout history. In the past, coal was used for heating homes and cooking. Nowadays, it's mostly used in power plants to generate electricity. When coal is burned, it releases heat, which is used to boil water and produce steam. The steam then turns turbines that generate electricity.

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    Environmental Impact

    While coal has been a significant source of energy, burning it also releases harmful gases and pollutants into the atmosphere, contributing to air pollution and climate change. As a result, there is growing interest in finding cleaner and more sustainable sources of energy to reduce our impact on the environment.

    Destructive Distillation of Coal

    Destructive distillation of coal is a process that involves heating coal in the absence of air. This process is used to extract various useful products from coal.
    When we burn coal in the presence of air, it produces heat and light, but it also releases gases like carbon dioxide, which can be harmful to the environment. Destructive distillation is a different process because we heat coal without letting it come in contact with air.

    During the process of destructive distillation, the coal undergoes a special kind of change. Instead of burning, it breaks down into different components, like coke, coal tar, and coal gas.

    Diagram of Destructive Distillation Coal - Science Grade 8

    1. Coke

    a) Coke is a black, porous, and tough substance that looks like a hard sponge.
    b) It is the purest form of coal, and we get it as a residue after heating coal without air (destructive distillation).
    c) Coke has many uses, especially in industries like steel manufacturing and metal extraction.
    d) When we heat coke with steam (water vapour), it reacts to produce water gas (a mixture of carbon monoxide and hydrogen).
    C + H2O → CO + H2
    e) Also, when we burn coke with air (oxygen and nitrogen), it reacts to form producer gas (a mixture of carbon monoxide and nitrogen).
    2C + O2 + 4N2 → 2CO + 4N2

    2. Coal Tar

    a) Coal tar is a thick, black liquid with a strong and unpleasant smell.
    b) We obtain coal tar through fractional distillation of coal tar, which means we separate it into different components based on their boiling points.
    c) Coal tar is valuable because it serves as a starting material for making various products, including medicines, explosives, naphthalene balls, and more.

    3. Coal Gas

    a) Coal gas is a mixture of gases, including hydrogen, carbon monoxide, methane, and others.
    b) It is a fuel with a high calorific value, which means it releases a lot of heat when burned.
    c) In the past, coal gas was widely used for street lighting, but now it is primarily used as a source of heat in industries.

    Flow Chart of Destructive Distillation of Coal - Science Grade 8


    a) Petroleum is a dark, oily liquid that is found deep beneath the Earth's surface. It is also known as "crude oil." This special liquid is made up of many different substances, like petrol, diesel, kerosene, lubricating oil, and more. These substances are separated from petroleum through a process called "refining," which is like sorting them based on their different boiling points.
    b) Millions of years ago, there were tiny plants and animals living in the oceans. When these living things died, their remains sank to the ocean floor and got buried under layers of sand and mud. Over time, the pressure and heat from the Earth's crust transformed these remains into petroleum. So, we can say that petroleum is a "fossil fuel" because it comes from the fossils of ancient plants and animals.
    c) Petroleum is a crucial resource because it provides us with many things we use every day. For example:

    • Petrol: We use petrol to fuel cars, motorcycles, and scooters, allowing us to travel long distances easily.
    • Diesel: Diesel is used to power heavy vehicles like trucks and buses, making transportation of goods and people more efficient.
    • Kerosene: Kerosene is used for cooking and lighting in some parts of the world.
    • Lubricating oil: This type of oil helps reduce friction and wear in machines and engines, keeping them running smoothly.

    d) In addition to these products, petroleum is also a starting material for making various everyday items, like plastics, synthetic rubber, medicines, and even some clothes.
    e) However, while petroleum is valuable and essential, it's essential to be mindful of its impact on the environment. Burning petroleum for energy releases harmful gases like carbon dioxide, which can contribute to climate change and air pollution. That's why scientists and researchers are continuously exploring cleaner and more sustainable energy sources to protect our planet.
    f) In conclusion, petroleum is a precious natural resource that has shaped the modern world and our lives in many ways. It's vital to use it wisely and seek alternatives to ensure a healthier and greener future for everyone.

    Petroleum and Natural Gas formation - Definition, types and examples

    Refining of Petroleum

    a) Refining petroleum is a fascinating process that helps us separate the different useful substances present in crude oil (petroleum).
    b) Crude oil is a mixture of many different substances, like petrol, diesel, kerosene, and more. However, these substances are all mixed up together in crude oil. To use them effectively, we need to separate them from one another.
    c) Refining is like a big sorting process for crude oil. It takes place in massive industrial facilities called "refineries."

    Steps Involved in Refining of Petroleum:

    1. Heating: First, the crude oil is heated to very high temperatures in a big column called a "fractionating tower." Different substances in crude oil have different boiling points. So, when we heat the crude oil, the substances with lower boiling points start to turn into vapours (gases), while the ones with higher boiling points remain as liquids.

    2. Separation: As the vapours rise up the fractionating tower, they cool down and condense back into liquids at different levels based on their boiling points. This separation process allows us to collect different substances at different levels of the tower.

    3. Collection: The substances with lower boiling points, like petrol and natural gas, rise up higher in the tower and are collected at the top. The ones with higher boiling points, like diesel and kerosene, condense and are collected at lower levels.

    4. Further Processing: After separating the main substances, some additional processes might be done to make the products even more useful. For example, petrol and diesel might undergo further treatments to improve their quality and performance.

    Refining of Petroleum - Science Grade 8

    Natural Gas

    a) Natural gas is a fascinating and important natural resource that has many uses in our daily lives.
    b) It is found deep inside the Earth, just like oil. It is made mostly of a substance called "methane," which is a type of molecule made up of carbon and hydrogen atoms.

    Formation of Natural Gas

    a) Millions of years ago, tiny plants and animals lived in the oceans. When they died, their remains sank to the bottom of the sea and got buried under layers of sand and mud. Over a very long time, heat and pressure from the Earth's crust transformed these remains into natural gas.
    b) One of the interesting things about natural gas is that it's stored under high pressure. When we compress it even more, it becomes "Compressed Natural Gas" (CNG), which is used as fuel for certain vehicles. CNG is considered environmentally friendly because it produces fewer pollutants compared to traditional fuels.
    c) However, it's essential to use natural gas responsibly. While it has many benefits, burning natural gas can still release greenhouse gases that contribute to climate change.

    Uses of Natural Gas

    1. Cooking: Natural gas is used in many homes for cooking. It provides a clean and efficient flame to cook our food quickly and easily.

    2. Heating: It's also used for heating homes and buildings during colder months. Natural gas furnaces and heaters keep us warm and cosy.

    3. Electricity: Natural gas plays a big role in generating electricity. It's used in power plants to produce electricity that lights up our homes and powers our electronic devices.

    4. Transportation: Some vehicles, like buses and trucks, use natural gas as fuel. It's considered a cleaner alternative to gasoline and diesel, as it produces fewer harmful emissions.

    5. Industry: Many industries use natural gas as a source of energy for their operations. It helps power machines and equipment used in manufacturing and production.

    In conclusion, natural gas is a versatile and valuable resource that powers our homes, industries, and transportation. It's essential to use it wisely and look for ways to balance our energy needs with environmental conservation for a better and greener future.

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