Combustion is a chemical process in which a substance reacts with oxygen, releasing energy in the form of heat and light. This process is essential in everyday life, as it powers vehicles, generates electricity, and provides heat for cooking. Combustion can occur in various forms, such as complete combustion, where the fuel burns completely with oxygen, and incomplete combustion, where the fuel burns partially, producing harmful substances like carbon monoxide. In this chapter, students will learn about the types of combustion, the factors affecting it, and the importance of fuels in daily life. Understanding combustion is crucial for managing energy use and reducing pollution.

Class 8 Science Ch 5 Combustion Oxford

Class 8 Science Ch 5 Combustion Oxford

Objective type questions

A. Fill in the blanks with the correct words.

1. ……………(Inflammable/Non-flammable) substances have low ignition temperature.

2. Non-luminous flame is of ………..(blue/yellow) colour.

3. ……..(Outer/Inner) zone is the coolest part of the flame.

4. …….(Exhaustible/Inexhaustible) natural resources have limited availability in nature.

5. ……..(Coal/Natural gas) was formed from the remains of plants.

6……….. (Extraction/Refining) of petroleum is done to separate petroleum into useful products.

Ans:

Inflammable substances have low ignition temperature.
(✅ Inflammable / Non-flammable)

Non-luminous flame is of blue colour.
(✅ blue / yellow)

Inner zone is the coolest part of the flame.
(✅ Inner / Outer)

Exhaustible natural resources have limited availability in nature.
(✅ Exhaustible / Inexhaustible)

Coal was formed from the remains of plants.
(✅ Coal / Natural gas)

Refining of petroleum is done to separate petroleum into useful products.
(✅ Refining / Extraction)

B. Choose the correct option.

1. The colour of the flame depends upon:

a. temperature

b. amount of air available

c. nature of the substance burning

d. All of these

2. What burns in a candle flame?

a. Solid wax

b. Liquid wax

c. Wax vapours

d. Oxygen

3. Which of the following is produced in incomplete combustion of hydrocarbons?

a. Carbon dioxide

b. Carbon monoxide

c. Oxygen

d. Methane

4. Which of the following is a characteristic of an ideal fuel?

a. High calorific value

c. Low ignition temperature

5. Which of the following is the main constituent of natural gas?

a. Oxygen

b. Petrol

c. Methane

d. Carbon dioxide

b. High rate of combustion

d. Should cause pollution

b. Oxides of nitrogen and sulphur

d. All of these

6. Which of the following is an air pollutant?

a. Carbon monoxide

c. Soot particles

7. In which of the following cases, water should not be used for extinguishing fire?

a. Burning diesel

b. Burning petrol

c. Electrical fire

d. All of these

8. Which of the following fuels is considered an ideal fuel for domestic use?

a. Hydrogen

b. Petrol

c. Cow dung cakes

d. Methane

9. Which of the following types of coal is used for manufacturing coke?

a. Lignite

b. Peat

c. Bituminous coal

d. Anthracite

10. Which of the following products of petroleum is used in candles, ointments and Vaseline?

a. Fuel oil

b. Paraffin wax

c. Lubricating oil

d. Asphalt

Ans:

The colour of the flame depends upon:
✅ d. All of these

What burns in a candle flame?
✅ c. Wax vapours

Which of the following is produced in incomplete combustion of hydrocarbons?
✅ b. Carbon monoxide

Which of the following is a characteristic of an ideal fuel?
✅ a. High calorific value

Which of the following is the main constituent of natural gas?
✅ c. Methane

Which of the following is an air pollutant?
✅ d. All of these
(Carbon monoxide, oxides of nitrogen and sulphur, soot particles)

In which of the following cases, water should not be used for extinguishing fire?
✅ d. All of these
(Water should not be used on oil fires or electrical fires.)

Which of the following fuels is considered an ideal fuel for domestic use?
✅ d. Methane
(Main component of LPG and natural gas)

Which of the following types of coal is used for manufacturing coke?
✅ c. Bituminous coal

Which of the following products of petroleum is used in candles, ointments and Vaseline?
✅ b. Paraffin wax

C. Match the following.

Column A                                                      Column B

  1. Oxides of sulphur and nitrogen            a. Methane

 2. Domestic fuel                                            b. White phosphorous

3. Diesel                                                           c. Carbon dioxide

4. Spontaneous combustion                         d. Acid rain

5. Fire extinguisher                                         e. Heavy motor vehicles

Ans:

  1. Oxides of sulphur and nitrogen → d. Acid rain
  2. Domestic fuel → a. Methane
  3. Diesel → e. Heavy motor vehicles
  4. Spontaneous combustion → b. White phosphorous
  5. Fire extinguisher → c. Carbon dioxide

II. Very short answer type questions

A. Give one word for the following.

1. Burning of a substance in the presence of air or oxygen with the liberation of heat and light

2. The combustion which takes place in adequate amount of air or oxygen

3. A region where combustion of fuel takes place

4. Flame that emits a lot of light

5. The amount of heat produced in kilojoules when one gram of fuel is completely burned

6. The resources which have limitless supply

III. Short answer type questions

1. Burning of a substance in the presence of air or oxygen with the liberation of heat and light
✅ Combustion

2. The combustion which takes place in adequate amount of air or oxygen
✅ Complete combustion

3.A region where combustion of fuel takes place
✅ Combustion chamber

4.Flame that emits a lot of light
✅ Luminous flame

5.The amount of heat produced in kilojoules when one gram of fuel is completely burned
✅ Calorific value

6.The resources which have limitless supply
✅ Inexhaustible resources

IV. Long answer type questions

1. Write any one difference between the following.

a. Combustible and non-combustible substances.

b. Rapid and spontaneous combustion

c. Complete combustion and incomplete combustion

d. Blue and yellow flame

e. Exhaustible and inexhaustible natural resources

Ans:

a. Combustible and non-combustible substances:

  • Combustible substances can catch fire and burn when exposed to heat, while non-combustible substances do not burn under normal conditions.

b. Rapid and spontaneous combustion:

  • Rapid combustion occurs quickly with a visible flame when a substance burns in the presence of oxygen, while spontaneous combustion happens without an external flame or spark, often due to heat buildup inside a substance.

c. Complete combustion and incomplete combustion:

  • Complete combustion occurs when a substance burns with sufficient oxygen, producing carbon dioxide and water, while incomplete combustion occurs with insufficient oxygen, producing carbon monoxide, carbon (soot), and water.

d. Blue and yellow flame:

  • A blue flame indicates complete combustion, is hotter, and produces less soot, while a yellow flame indicates incomplete combustion, is cooler, and produces more soot.

e. Exhaustible and inexhaustible natural resources:

  • Exhaustible resources are limited in supply and can be depleted (e.g., coal, petroleum), while inexhaustible resources are available in unlimited quantities and cannot be depleted (e.g., solar energy, wind).

2. Explain the different zones of a candle flame.

3. What are fossil fuels? How were coal and petroleum

Objective type questions

A. Fill in the blanks with the correct words.

1. ……………(Inflammable/Non-flammable) substances have low ignition temperature.

2. Non-luminous flame is of ………..(blue/yellow) colour.

3. ……..(Outer/Inner) zone is the coolest part of the flame.

4. …….(Exhaustible/Inexhaustible) natural resources have limited availability in nature.

5. ……..(Coal/Natural gas) was formed from the remains of plants.

6……….. (Extraction/Refining) of petroleum is done to separate petroleum into useful products.

Ans:

  1. Inflammable substances have low ignition temperature.
  2. Non-luminous flame is of yellow colour.
  3. Inner zone is the coolest part of the flame.
  4. Exhaustible natural resources have limited availability in nature.
  5. Coal was formed from the remains of plants.
  6. Refining of petroleum is done to separate petroleum into useful products.

B. Choose the correct option.

1. The colour of the flame depends upon:

a. temperature

b. amount of air available

c. nature of the substance burning

d. All of these

2. What burns in a candle flame?

a. Solid wax

b. Liquid wax

c. Wax vapours

d. Oxygen

3. Which of the following is produced in incomplete combustion of hydrocarbons?

a. Carbon dioxide

b. Carbon monoxide

c. Oxygen

d. Methane

4. Which of the following is a characteristic of an ideal fuel?

a. High calorific value

c. Low ignition temperature

5. Which of the following is the main constituent of natural gas?

a. Oxygen

b. Petrol

c. Methane

d. Carbon dioxide

b. High rate of combustion

d. Should cause pollution

b. Oxides of nitrogen and sulphur

d. All of these

6. Which of the following is an air pollutant?

a. Carbon monoxide

c. Soot particles

7. In which of the following cases, water should not be used for extinguishing fire?

a. Burning diesel

b. Burning petrol

c. Electrical fire

d. All of these

8. Which of the following fuels is considered an ideal fuel for domestic use?

a. Hydrogen

b. Petrol

c. Cow dung cakes

d. Methane

9. Which of the following types of coal is used for manufacturing coke?

a. Lignite

b. Peat

c. Bituminous coal

d. Anthracite

10. Which of the following products of petroleum is used in candles, ointments and Vaseline?

a. Fuel oil

b. Paraffin wax

c. Lubricating oil

d. Asphalt

Ans:

  1. The colour of the flame depends upon:
    • d. All of these
  2. What burns in a candle flame?
    • c. Wax vapours
  3. Which of the following is produced in incomplete combustion of hydrocarbons?
    • b. Carbon monoxide
  4. Which of the following is a characteristic of an ideal fuel?
    • a. High calorific value
  5. Which of the following is the main constituent of natural gas?
    • c. Methane
  6. Which of the following is an air pollutant?
    • a. Carbon monoxide (Note: Both carbon monoxide and soot particles can be pollutants, but carbon monoxide is more directly harmful as a gas.)
  7. In which of the following cases, water should not be used for extinguishing fire?
    • d. All of these
  8. Which of the following fuels is considered an ideal fuel for domestic use?
    • d. Methane
  9. Which of the following types of coal is used for manufacturing coke?
    • c. Bituminous coal
  10. Which of the following products of petroleum is used in candles, ointments and Vaseline?
  • b. Paraffin wax

C. Match the following.

Column A                                                      Column B

  1. Oxides of sulphur and nitrogen            a. Methane

 2. Domestic fuel                                            b. White phosphorous

3. Diesel                                                           c. Carbon dioxide

4. Spontaneous combustion                         d. Acid rain

5. Fire extinguisher                                         e. Heavy motor vehicles

Ans:

  1. Oxides of sulphur and nitrogen → d. Acid rain
  2. Domestic fuel → a. Methane
  3. Diesel → e. Heavy motor vehicles
  4. Spontaneous combustion → b. White phosphorous
  5. Fire extinguisher → c. Carbon dioxide

II. Very short answer type questions

A. Give one word for the following.

1. Burning of a substance in the presence of air or oxygen with the liberation of heat and light

2. The combustion which takes place in adequate amount of air or oxygen

3. A region where combustion of fuel takes place

4. Flame that emits a lot of light

5. The amount of heat produced in kilojoules when one gram of fuel is completely burned

6. The resources which have limitless supply

Ans:

  1. Combustion
  2. Complete combustion
  3. Flame
  4. Luminous flame
  5. Calorific value
  6. Inexhaustible resources

III. Short answer type questions

1. Why is water not always used for extinguishing fire?

Water is not always used for extinguishing fire because:

  • Electrical fires: Water is a good conductor of electricity and can cause electrocution if used on electrical fires.
  • Flammable liquids: Water can spread the fire if it is used on burning substances like oil or petrol, as these liquids are less dense than water and can float, spreading the fire further.

2. State any two characteristics of an ideal fuel.

  1. High calorific value: An ideal fuel should produce a large amount of heat when burned.
  2. Low ignition temperature: It should catch fire easily at a lower temperature, making it convenient to use.

3. Why are methane and LPG considered ideal for use as domestic fuels?

  • Methane and LPG (Liquefied Petroleum Gas) are considered ideal for domestic use because:
    1. High calorific value: They release a large amount of heat, making them efficient fuels.
    2. Clean burning: They burn completely with a blue, non-luminous flame, producing little to no smoke or soot, which is beneficial for indoor use.
    3. Easy to transport and store: They are available in cylinders, making them easy to store and transport.

4. List the different types of coal with their carbon content and one use.

  1. Peat:
    • Carbon content: 60-70%
    • Use: Primarily used as fuel for power plants in some regions, though it’s not very efficient.
  2. Lignite (Brown Coal):
    • Carbon content: 60-70%
    • Use: Used in power generation, but it has a high moisture content and low energy output.
  3. Bituminous coal:
    • Carbon content: 70-80%
    • Use: Used extensively in power plants, steel manufacturing, and as domestic fuel.
  4. Anthracite (Hard coal):
    • Carbon content: 80-95%
    • Use: Used in home heating, as it burns very cleanly and efficiently.

5. What are the various products obtained from refining of petroleum? Write one use for each.

  1. Gasoline (Petrol):
    • Use: Fuel for cars, motorcycles, and other vehicles.
  2. Kerosene:
    • Use: Used as a fuel for jet engines (aviation kerosene) and for heating and lighting in some areas.
  3. Diesel:
    • Use: Fuel for trucks, buses, and other heavy vehicles.
  4. Lubricating oil:
    • Use: Used to lubricate engines and machinery to reduce wear and tear.
  5. Paraffin wax:
    • Use: Used in candles, ointments, and for coating materials.
  6. Bitumen:
    • Use: Used for road construction (asphalt) and waterproofing.
  7. Liquefied Petroleum Gas (LPG):
    • Use: Used as a domestic fuel for cooking and heating.

IV. Long answer type questions

1. Write any one difference between the following:

Ans:

1. Combustible and non-combustible substances:

  • Combustible substances are materials that can burn in the presence of oxygen when heat is applied (e.g., wood, paper).
  • Non-combustible substances are materials that do not burn under normal conditions (e.g., water, stone).

2. Rapid and spontaneous combustion:

  • Rapid combustion is a process where a substance burns quickly and with a visible flame when exposed to heat and oxygen, often accompanied by a loud sound (e.g., burning paper).
  • Spontaneous combustion occurs when a substance catches fire on its own, without any external flame or spark, due to the buildup of heat inside the substance (e.g., oily rags).

3. Complete combustion and incomplete combustion:

  • Complete combustion occurs when a substance burns fully in the presence of sufficient oxygen, producing carbon dioxide and water (e.g., burning methane in a well-ventilated space).
  • Incomplete combustion happens when oxygen is insufficient, leading to the production of carbon monoxide, carbon (soot), and water, resulting in less heat and more pollution (e.g., burning coal with limited air supply).

4. Blue and yellow flame:

  • A blue flame is characteristic of complete combustion, indicating a hotter and cleaner burn with minimal soot (e.g., the flame of natural gas).
  • A yellow flame is associated with incomplete combustion, often cooler, and emits more light and soot due to the presence of carbon particles (e.g., a candle flame).

5. Exhaustible and inexhaustible natural resources:

  • Exhaustible resources are natural resources that have a limited supply and can be depleted with use, such as coal, petroleum, and natural gas.
  • Inexhaustible resources are resources that are abundant and cannot be exhausted by human use, such as solar energy, wind, and tidal energy.

2. Explain the different zones of a candle flame:

Ans: A candle flame consists of three main zones, each with distinct characteristics:

  1. Inner core (coolest part):
    • The innermost part of the flame is the dark zone or inner core, which is the coolest region of the flame.
    • In this zone, combustion is incomplete due to insufficient oxygen, and thus, no light is emitted. The temperature here is relatively low, and it is not visible.
  2. Middle zone (luminous zone):
    • This is the yellow zone where the flame produces visible light.
    • It is due to incomplete combustion, which causes the production of soot particles (carbon). The temperature here is hotter than the inner core but not as high as the outer zone.
  3. Outer zone (blue zone):
    • The outermost part of the flame is the hottest part, known as the blue zone.
    • In this zone, complete combustion occurs, meaning there is sufficient oxygen for the fuel to burn efficiently, producing carbon dioxide and water vapor. The flame here is blue and non-luminous, emitting very little light and heat compared to the middle zone.

3. What are fossil fuels? How were coal and petroleum formed?

Ans: Fossil fuels are energy sources derived from the remains of ancient plants and animals that have been buried and subjected to heat and pressure over millions of years. These fuels are rich in carbon and are burned to release energy. The three main types of fossil fuels are coal, petroleum, and natural gas.

Formation of Coal:

  • Coal is formed from the remains of plants, primarily ferns, trees, and other vegetation that lived millions of years ago in swampy, waterlogged environments.
  • As these plants died, they accumulated in layers and were buried under sediments. Over millions of years, heat and pressure caused the plant material to undergo chemical changes, resulting in the formation of coal.

Formation of Petroleum:

  • Petroleum is formed from the remains of tiny marine organisms, such as plankton and algae, that lived millions of years ago in oceans or seas.
  • These remains settled on the ocean floor and were buried under layers of sediment. The heat and pressure over time converted these remains into crude oil and natural gas. This crude oil is then refined to produce various petroleum products like gasoline, diesel, and kerosene.

Both coal and petroleum are considered non-renewable resources because they take millions of years to form, and their supply is limited.

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