NCERT Solutions for Class 8 Science Chapter 3 Combustion and Flame

NCERT Solutions for Class 8 Science Chapter 3  

Combustion and Flame Class 8 is an important chapter in NCERT Class 8 Science that helps students understand how substances burn and release energy. The chapter explains the process of combustion, different types of fuels, conditions required for burning, and the structure of a flame. Learning this chapter well helps students answer both theoretical and numerical questions in exams.

Students often search for combustion and flame class 8 questions and answers to revise important concepts like ignition temperature, inflammable substances, and calorific value. Practicing class 8 science ch 6 question answer sets makes it easier to understand real-life applications of combustion, such as fuel usage and fire safety.

For complete exam preparation, combustion and flame class 8 NCERT solutions are very useful. These solutions explain each question in a clear and step-by-step manner, making them ideal for quick revision. NCERT Class 8 Science combustion and flame solutions also help students learn correct answer formats for board exams.

If you want reliable and accurate explanations, combustion and flame class 8 solutions based on the latest NCERT syllabus are the best study resources to score well and build strong conceptual clarity.

Enroll Now for Kids Online Classes

Combustion and Flame Class 8 Questions and Answers

1. List conditions under which combustion can take place.

Soln:

The burning of a substance in the presence of oxygen is defined as combustion. The conditions under which combustion can take place are

• The presence of air or oxygen.
• The presence of fuel plays a significant role.
• Ignition temperature is maintained (It is defined as the substance that catches fire at its lowest temperature.)

2. Fill in the blanks.

(a) Burning of wood and coal causes __________of air.

(b) A liquid fuel, used in homes is__________.

(c) Fuel must be heated to its ____________ before it starts burning.

(d) The fire produced by oil cannot be controlled by___________ .

Soln:

(a) Burning of wood and coal causes pollution of air. (b) A liquid fuel, used in homes is kerosene . (c) Fuel must be heated to its ignition temperature before it starts burning. (d) The fire produced by oil cannot be controlled by water.

3. Explain how the use of CNG in automobiles has reduced pollution in our cities.

Soln:

Among cars, CNG contributes significantly to pollution reduction for the following reasons: In comparison, CNG is a cleaner fuel. As an alternative to petrol, diesel, and propane/LPG, consider using CNG. Compared to the other fuels indicated above, it typically contains a few more unwanted gases. When fuels like petroleum burn, a lot of unburned carbon particles are released into the air along with carbon monoxide, which can cause respiratory illnesses.

4. Compare LPG and wood as fuels.

Soln:

Wood

It is regarded as a conventional fuel that can be utilized for both household and commercial uses. A large amount of smoke from wood pollutes the air and leads to respiratory illnesses. Deforestation is largely caused by the consumption of timber. Wood has a calorific value of between 17,000 and 22,000 kJ/kg. On the other hand, wood can be used for a campfire or furnace outside as well as an indoor furnace, stove, or fireplace.

LPG

The application of Wood has been substituted by Liquefied Petroleum Gas (LPG). It doesn't emit any toxins or smoke. The fuel is cleaner. LPG has a higher fuel efficiency than wood. LPG has a calorific value of 55,000 kJ/kg. LPG is therefore the best option.

5. Give reasons.

(a) Water is not used to control fires involving electrical equipment.

(b) LPG is a better domestic fuel than wood.

(c) Paper by itself catches fire easily whereas a piece of paper wrapped around an aluminum pipe does not.

Soln:

a) Water is an excellent electrical conductor.

Water wouldn't do anything but spread the electricity in an electrical fire. Someone putting out the flames could receive an electric shock.

b) Unlike wood, which releases smoke and other pollutants, LPG is a cleaner fuel.

Conversely, wood produces a great deal of smoke and pollutants into the atmosphere, which contaminates it and causes respiratory illnesses. For this reason, LPG is a superior home fuel than wood.

c) Due to its low ignition temperature, the paper itself easily catches fire.

Because aluminum is an excellent electrical conductor, the sheet of paper wrapped around the pipe doesn't catch fire. However, the temperature at which paper is wrapped around an aluminum pipe rises. Therefore, heat is transferred from the paper to the aluminum pipe. It doesn't catch fire as a result.

6. Make a labeled diagram of a candle flame.

Soln:

7. Name the unit in which the calorific value of a fuel is expressed.

Soln:

Calorific value is defined as the energy contained in the fuel. It is expressed in the form kJ/kg kJ=kilo joules and kg=kilogram

8. Explain how CO ₂ can control fires.

Soln:

As a non-flammable gas, CO2 puts out the fire in two ways: (i) Because it weighs more than oxygen, it blankets the flames and prevents oxygen from coming into touch with fuel. (ii) CO2 is stored in liquid form in cylinders. When it is released, it greatly expands. This lowers the fuel's temperature, aiding in the containment of the fire.

9. It is difficult to burn a heap of green leaves but dry leaves catch fire easily. Explain.

Soln:

The high igniting temperature of a pile of green leaves is caused by their high moisture content. It does not readily catch fire as a result. However, dried leaves have a low ignition temperature because they are devoid of moisture. As a result, they burn easily.

10. Which zone of a flame does a goldsmith use for melting gold and silver and why?

Soln:

The non-luminous flame, which is thought to be the outermost portion of the flame, is mostly used by goldsmiths. Because the outermost flame completely burns and is thought to be the hottest component of the flame, this portion of the flame is used.

11. In an experiment, 4.5 kg of fuel was completely burnt. The heat produced was measured to be 180,000 kJ. Calculate the calorific value of the fuel.

Soln:

12. Can the process of rusting be called combustion? Discuss.

Soln:

No, because heat is released during the rusting process, rusting is an exothermic reaction. In contrast, combustion is a chemical reaction that releases energy in the form of light or heat when a material combines with oxygen.

13. Abida and Ramesh were doing an experiment in which water was to be heated in a beaker. Abida kept the beaker near the wick in the yellow part of the candle flame. Ramesh kept the beaker in the outermost part of the flame. Whose water will get heated in a shorter time?

Soln:

Given that it is the hottest area of the flame and is considered non-luminous, water placed in its outermost part will heat up quickly. Thus, we shall heat Ramesh's beaker first. On the other hand, Abida, who positioned the beaker in the yellow flame, is relatively less heated.

Read More: What is Temperature?

Mastering Combustion and Flame Class 8 Questions and Answers

To excel in your exams, you don't just need to memorize; you need to understand that combustion is a chemical reaction. When a substance reacts with oxygen to give off heat, we call it combustion. Some materials catch fire easily, while others don't. These are classified as combustible and non-combustible substances. Knowing the difference is a vital part of your science foundation.

What is Ignition Temperature?

Every type of fuel has a certain "tipping point." This is the lowest temperature at which something will catch fire. You probably know that a piece of paper burns up virtually right away, while a thick log of wood takes a while. The wood needs more heat to achieve the temperature at which it will catch fire. LPG and petrol are two examples of flammable substances. These are things that catch fire easily when a spark hits them.

Detailed Breakdown of Combustion and Flame Class 8 Questions and Answers NCERT

Conditions Necessary for Combustion

For a fire to start and keep going, three components must be present at the same moment. The fire will go out if you take away even one of these.

• Fuel: There has to be something to burn.

• Air (Oxygen): Oxygen helps things burn.

• Heat: To make the fuel hotter than the point at which it will catch fire.

When we use a fire extinguisher, we are either cutting off the air supply or lowering the temperature of the fuel. For example, carbon dioxide ($CO_2$) is heavier than oxygen. It wraps around the fire like a blanket, keeping the oxygen from getting to the fuel.

Different Types of Combustion

Fires don't all act the same way. We put them into groups based on how quickly they happen:

• Fast Combustion: Imagine a cooker that runs on gas. When you put a lit matchstick close to it, the gas catches fire right away, generating heat and light.

• Combustion on its own: This is quite risky. It happens when something unexpectedly catches fire for no clear reason. This can happen when coal dust in mines catches fire.

• Blast: This happens when crackers are lit. A quick reaction happens, and a lot of gas, heat, light, and sound are released.

The Zones of a Flame

If you look attentively at a candle flame, you'll discover that it's not just one colour. There are three separate areas:

• Outer Zone: This is the hottest region of the outer zone. It's blue because this is where full combustion happens.

• Middle Zone: This area is yellow and moderately heated. Here, combustion is not complete.

• Innermost Zone: This is the portion that is the least heated. It looks dark because there are carbon particles that haven't burned.

Combustion and Flame Class 8 Extra Questions and Answers 

How to Control Fire

Water is the most common fire extinguisher, but it doesn't work for everything. You can't use water on electrical fires because water conducts electricity and might give you a shock. Similarly, you shouldn't use water for oil fires. Since oil is lighter than water, it floats to the top and keeps burning. In these cases, $CO_2$ is the best option because it doesn't harm electrical equipment and effectively smothers the flames.

Choosing the Right Fuel

A good fuel is one that is readily available, cheap, and burns easily in air at a moderate rate. It should produce a large amount of heat without leaving behind undesirable residues. At the end of the day, there's probably no fuel that we can consider a "perfect" fuel. We look for the one that fulfills most requirements for a specific use.

The efficiency of a fuel is measured by its Calorific Value. This is the amount of heat energy produced on complete combustion of 1 kg of a fuel. It's expressed in a unit called kilojoule per kg ($kJ/kg$).

Environmental Hazards of Burning Fuel

When you burn fuels, they let off carbon particles, carbon monoxide, and carbon dioxide.

• Global Warning: People think that more $CO_2$ in the air makes the Earth warmer.

• Acid Rain: Burning coal and fuel releases sulphur dioxide, which causes acid rain. Petrol engines make nitrogen oxides. When it rains, these gases mix with the water to make acids that harm buildings and crops.

• Problems with breathing: Unburnt carbon particles are harmful pollutants that can cause respiratory illnesses like asthma.

Read More: Light

How CuriousJr Online Tuition Classes Help Your Child Learn Better

CuriousJr’s online tuition classes are thoughtfully designed for students from Class 3 to Class 8, focusing on building strong academic foundations and improving overall learning confidence. These school tuition classes follow a structured and child-friendly approach that makes learning simple, engaging, and effective.

One of the key highlights of CuriousJr is its daily interactive classes. These sessions encourage active participation, helping students understand concepts clearly instead of memorising them. Interactive teaching methods make lessons enjoyable and improve long-term retention.

CuriousJr offers complete coverage of core subjects such as Maths, Science, English, and Social Studies, strictly following the latest school syllabus. This ensures that students stay in sync with their classroom learning and perform better in school exams.

Regular tests and assessments play an important role in tracking a child’s progress. Detailed feedback helps identify strengths and learning gaps, allowing students to improve step by step without pressure. Overall, CuriousJr online tuition classes create a supportive learning environment that helps children learn better and succeed academically.