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4.10 - Exercises

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Conditions for Combustion

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Teacher
Teacher

Today, we're discussing the conditions needed for combustion. Can anyone tell me what those conditions are?

Student 1
Student 1

Does it need fuel?

Teacher
Teacher

Yes! Fuel is essential. What else must be present?

Student 2
Student 2

Oxygen from air, right?

Teacher
Teacher

Exactly! Oxygen is crucial. And lastly?

Student 3
Student 3

Heat is needed too!

Teacher
Teacher

Correct! These three elements: fuel, oxygen, and heat are necessary for combustion, often remembered by the acronym 'FOH'.

Student 4
Student 4

What happens if any of those is missing?

Teacher
Teacher

That's a great question! Without any one of these, combustion won’t occur. Can you think of a real-life example?

Student 1
Student 1

Like a candle going out when we cover it?

Teacher
Teacher

Exactly. Great observation! So remember, 'FOH' is key to combustion.

Different Fuels and Their Properties

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Teacher
Teacher

Now let’s explore different types of fuels. Can anyone name some fuels?

Student 2
Student 2

Wood, coal, petrol, and LPG!

Teacher
Teacher

Good list! Let's categorize them into solid, liquid, and gas. Which fits where?

Student 3
Student 3

Wood and coal are solid. Petrol and kerosene are liquids, and LPG is a gas.

Teacher
Teacher

Well done! Now, why do you think LPG is preferred over wood?

Student 4
Student 4

Because it burns cleaner and produces less smoke.

Teacher
Teacher

Exactly! Cleaner burning fuels like LPG or CNG help reduce air pollution. Remember, cleaner combustion means a healthier environment.

Understanding Ignition Temperature

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Teacher
Teacher

Let’s discuss ignition temperature. What do we mean by that term?

Student 1
Student 1

Is it the temperature when something catches fire?

Teacher
Teacher

Correct! It’s the lowest temperature required to ignite a fuel. Can you think of a fuel with a low ignition temperature?

Student 2
Student 2

Kerosene oil can catch fire easily when heated a bit!

Teacher
Teacher

Excellent example! Kerosene’s ignition temperature is lower than that of wood, which is why it catches fire more easily.

Student 3
Student 3

So that’s why we have to be careful with it!

Teacher
Teacher

Exactly! Understanding ignition temperature helps us handle fuels safely.

Introduction & Overview

Read a summary of the section's main ideas. Choose from Basic, Medium, or Detailed.

Quick Overview

This section provides exercises related to combustion and flame, aiming to reinforce understanding of key concepts through practical application.

Standard

The exercises focus on testing knowledge about combustion, the properties of fuels, and the characteristics of flames. They include fill-in-the-blank questions, comparisons, and problem-solving tasks, encouraging students to apply what they have learned in practical scenarios.

Detailed

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Grade 8 | Science | Combustion | Free Tutorial | CBSE | ICSE | State Board
Grade 8 | Science | Combustion | Free Tutorial | CBSE | ICSE | State Board

Audio Book

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Conditions for Combustion

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  1. List conditions under which combustion can take place.

Detailed Explanation

For combustion to occur, three essential conditions must be met: there must be fuel, oxygen (typically from the air), and heat. Fuel refers to any combustible material like wood, kerosene, or coal. Oxygen is necessary for the reaction to happen, as it supports the combustion process. Heat is needed to raise the fuel to its ignition temperature, allowing it to start burning. If any one of these conditions is absent, combustion cannot take place.

Examples & Analogies

Imagine trying to start a campfire. You need dry wood (fuel), a lighter or matches (heat), and a place where air can flow (oxygen). If you have wet wood, no matches, or if the campfire is in a closed box, you won’t be able to start the fire.

Fill in the Blanks

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  1. 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) Fire produced by oil cannot be controlled by     .

Detailed Explanation

This exercise emphasizes understanding key concepts related to combustion. For part (a), burning wood and coal leads to the depletion of oxygen in the air. Part (b) refers to kerosene as a common liquid fuel used in households. For part (c), the temperature to which a fuel must be heated to ignite is known as its ignition temperature. Finally, part (d) states that water is not effective for extinguishing oil fires because oil floats on top of water and continues to burn.

Examples & Analogies

Think of a firepit. As you burn wood, it uses up the oxygen in the air around it. If you’ve ever used kerosene to start a fire, you know it makes things go up in flames quickly! Just like how you can't put out an oil fire with water, you can't put a swimming pool on top of a water fountain; it just wouldn't work!

CNG and Pollution Reduction

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

Detailed Explanation

Compressed Natural Gas (CNG) has been adopted in many vehicles because it burns cleaner than gasoline or diesel. It produces fewer harmful emissions, such as carbon monoxide and carbon dioxide, which are responsible for air pollution and contribute to global warming. By switching to CNG, cities have experienced improvements in air quality and a reduction in smog and respiratory issues among residents.

Examples & Analogies

Consider a bustling city where cars once puffed out black smoke. By using CNG, it’s like replacing a smoky barbecue with a clean electric grill; the air is fresher, and people can breathe easier without the haze of pollution.

LPG vs Wood

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  1. Compare LPG and wood as fuels.

Detailed Explanation

Liquefied Petroleum Gas (LPG) is a cleaner, more efficient fuel compared to wood. LPG burns at a higher temperature, produces less smoke, and leaves no residue, making it more environmentally friendly. In contrast, burning wood can produce significant amounts of smoke and unburnt carbon particles, which are harmful to health. LPG is more convenient as it is easy to store and transport, while wood requires chopping and can be less readily available.

Examples & Analogies

If you think about cooking, using a gas stove (LPG) is like using a microwave oven—fast, clean, and efficient—whereas cooking over an open fire with wood is similar to using an old-fashioned campfire, a lot of effort and cleanup afterward!

Reasons for Observations

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  1. 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 aluminium pipe does not.

Detailed Explanation

For part (a), water can conduct electricity, making it dangerous to use on electrical fires, which could lead to electric shocks. Part (b) explains that LPG burns more cleanly and efficiently than wood, producing less harmful smoke. For part (c), the aluminum pipe acts as a heat sink, meaning the paper does not reach its ignition temperature, preventing it from burning, whereas exposed paper has direct access to heat.

Examples & Analogies

Picture pouring water on an electrical appliance that’s on fire—it could not only fail to extinguish the fire but could also hurt you! Cooking with LPG is like using the easiest tool in your toolbox instead of a hammer and a wedge (wood): it just works better without the mess and effort.

Candle Flame Diagram

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  1. Make a labelled diagram of a candle flame.

Detailed Explanation

Creating a diagram of a candle flame involves identifying and labeling its three distinct zones: the dark zone (where wax vaporizes), the luminous zone (where the flame glows due to combustion of wax vapors), and the non-luminous zone (which is significantly hotter and blue). Each of these zones plays a crucial role in understanding how a flame works.

Examples & Analogies

Think of a candle flame like an ice cream cone: the bottom (dark zone) is what holds it up, the middle (luminous zone) is the flavor everyone sees, and the top (non-luminous zone) is where it melts away and gets hot. Each part has its job in making the whole candle function.

Calorific Value Unit

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

Detailed Explanation

The calorific value, which measures the energy produced by the complete combustion of a fuel, is expressed in kilojoules per kilogram (kJ/kg). This unit helps us compare the energy content of various fuels, allowing us to choose the most efficient one for our needs.

Examples & Analogies

Think of calorific value like comparing the power of different batteries: just like you’d want to buy a battery that lasts longer, you want fuels that give you more energy. The higher the number in kJ/kg, the better the fuel!

CO2 and Fire Control

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  1. Explain how CO2 is able to control fires.

Detailed Explanation

Carbon dioxide (CO2) extinguishes fire by displacing oxygen around the fire. Since fire requires oxygen to sustain combustion, reducing the oxygen supply effectively extinguishes the flame. CO2 is also cooler than burning materials, further preventing combustion from continuing.

Examples & Analogies

Imagine blowing out a birthday cake candle. Just like your breath pushes away the oxygen around the flame, CO2 smothers the fire, making it impossible for it to keep burning. It’s like putting a blanket over a flame to quench it!

Green vs Dry Leaves

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

Detailed Explanation

Green leaves contain moisture, which makes it hard for them to reach their ignition temperature. When leaves are dry, they lack this moisture and can reach combustion temperatures much easier; hence they burn quickly. Dry leaves have lower water content and more combustibles, making them efficient fuel.

Examples & Analogies

Try lighting fresh spinach versus dried herbs for cooking. The spinach (green leaves) is too wet to catch fire as easily as the dried herbs are; it’s a bit like trying to start a campfire with wet matchsticks versus dry ones!

Goldsmiths and Flame Zones

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

Detailed Explanation

Goldsmiths usually use the outer zone of the flame because it is the hottest zone and provides sufficient heat to melt metals like gold and silver. This area of the flame has a higher temperature due to complete combustion, making it efficient for such tasks.

Examples & Analogies

Think of cooking on a stove: if you want to boil water quickly, you turn the burner to its highest setting, just like a goldsmith goes for the hottest part of the flame to get the job done efficiently!

Fuel Calorific Calculation

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

Detailed Explanation

To calculate the calorific value, divide the total heat produced by the mass of the fuel burned. The formula is: Calorific Value = Total Heat Produced / Mass of Fuel. Here, you divide 180,000 kJ by 4.5 kg, which gives you the calorific value in kJ/kg.

Examples & Analogies

It’s just like determining how much energy you get from a snack. If you know the total energy and the serving size, you can find out how many kilojoules are in each serving!

Rusting vs Combustion

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

Detailed Explanation

Rusting is a slow oxidation process involving iron reacting with oxygen and moisture, which results in iron oxide (rust). Unlike combustion, which is a rapid exothermic reaction releasing energy, rusting is a slow, generally non-exothermic process. Thus, while both involve oxygen, the nature and speed of the reactions differ significantly.

Examples & Analogies

Think of combustion like a fireworks show—quick and explosive—while rusting is like watching paint dry; it’s slow and unexciting but eventually leads to a change.

Heating Water Experiment

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  1. 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?

Detailed Explanation

Ramesh's water will get heated in a shorter time because the outermost part of the flame is the hottest zone. The yellow part of the candle flame (where Abida placed her beaker) is less hot compared to the blue flame (the outer zone) which burns at a higher temperature, allowing for quicker heat transfer and faster heating of the water.

Examples & Analogies

If you were drying clothes outside on a sunny day, those left in the sun (the hottest spot) dry faster than those left in the shade; similarly, Ramesh's water is being heated quicker!

Extended Learning Activities

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Extended Learning — Activities and Projects:
1. Survey the availability of various fuels in your locality...
2. Find out the number, type and location of fire extinguishers available in your school...
3. Survey 100 houses in your area...
4. Talk to people who use LPG at home...
5. Make a model of a fire extinguisher...

Detailed Explanation

These activities aim to engage students in real-world applications of concepts learned in class. Surveys on fuel availability and pollution help students understand fuel sources and their implications on the environment. Understanding fire safety through extinguisher locations establishes awareness of safety measures. Making a fire extinguisher model creatively illustrates principles explored in lessons about combustion and fire control.

Examples & Analogies

Think of these projects as a community treasure hunt: just like finding hidden gems teaches you about your surroundings, these activities deepen your understanding of how combustion affects your daily life and the importance of safety!

Definitions & Key Concepts

Learn essential terms and foundational ideas that form the basis of the topic.

Key Concepts

  • Fuel: A substance that can burn to produce energy.

  • Combustion: The process of burning that gives off heat and light.

  • Ignition Temperature: The lowest temperature at which a fuel will ignite.

  • Inflammable: A term describing materials that ignite easily.

Examples & Real-Life Applications

See how the concepts apply in real-world scenarios to understand their practical implications.

Examples

  • Candle wax is a common fuel that burns to produce light and heat.

  • Dry leaves catch fire easily due to their low ignition temperature compared to wet leaves.

Memory Aids

Use mnemonics, acronyms, or visual cues to help remember key information more easily.

🎵 Rhymes Time

  • Fire needs fuel that's dry and light, with oxygen to flare up bright!

📖 Fascinating Stories

  • Once in a forest, a small spark met dry leaves and said, 'Let's ignite!' And with air around, a fire danced into the night.

🧠 Other Memory Gems

  • Remember 'FOH' for Fire: Fuel, Oxygen, Heat!

🎯 Super Acronyms

F.O.H stands for Fuel, Oxygen, and Heat, the essentials for combustion.

Flash Cards

Review key concepts with flashcards.

Glossary of Terms

Review the Definitions for terms.

  • Term: Combustion

    Definition:

    A chemical process where a substance reacts with oxygen, producing heat and light.

  • Term: Ignition Temperature

    Definition:

    The minimum temperature at which a combustible substance catches fire.

  • Term: Fuel

    Definition:

    Any substance that can combust to produce energy.

  • Term: Inflammable Substances

    Definition:

    Materials that catch fire easily at low temperatures.