Revision Notes For CBSE Class 8 Science Chapter 6 - Combustion And Fame

1. Combustion:

The process in which a substance undergoes a chemical reaction in the presence of air (oxygen) to produce heat and light is called combustion.

The substance which undergoes combustion is called combustible. Combustion cannot take place in absence of oxygen. 

Ignition Temperature:

The lowest temperature at which a combustible substance catches fire under given pressure conditions is called ignition temperature. 

The substances which have very low ignition temperature and can easily catch fire with a flame are called inflammable substances.

Controlling Fire:

Fire can be controlled by removing one or more requirements essential for producing fire. 

Water is commonly used to control fires caused by substances other than oils and electrical equipment as it can worsen the conditions. 

As water cannot be used to control fires involving electrical equipment or oils, a fire extinguisher or sand is used to put out the fire.

Types of Combustion

The type of combustion depends upon the type of fuel used. Combustions are classified on the basis of nature and intensity, which are of three types. They are: 

1. Rapid Combustion:

When a substance burns rapidly and produces heat and light, such combustion is called rapid combustion. For example, the burning of a matchstick, gas stove.

2. Spontaneous Combustion: 

The type of combustion in which a material suddenly bursts into flames, without the application of any apparent cause is called spontaneous combustion. For example, burning of phosphorus, burning of camphor.

3. Explosion:

A large amount of gas formed in the reaction is liberated. Such a reaction is called an explosion. For example, a firecracker, missiles.

2. Flame:

It is a zone or burning vapour caused by substances during combustion. For example Kerosene oil and LPG gas, coal etc. 

Zones of a Flame:

There are Three Different Zones of a Flame – 

• Dark Zone: Near the surface of a combustible substance which is the least hot due to incomplete combustion.

• Luminous Zone: Brightest zone due to partial combustion.

• Non-luminous Zone: The outermost part of the flame which is the hottest zone due to complete combustion. 

3. Fuel:

Fuel is any substance that undergoes combustion to obtain energy that can be used to heat or move another object.

Property of a Good Fuel:

A good fuel must: 

• Be readily available.

• Be cheap.

• Burn easily at a moderate rate. 

• Should have high calorific value.

• Not leave behind any undesirable substances after combustion.

Fuel efficiency is expressed in terms of its calorific value which is the amount of heat energy produced on complete combustion of 1 kg of fuel and is expressed in units of kilojoule per kg(kJ/kg).

Types of Fuels: 

1. Solid Fuels: solid fuels are combustible substances that are solid at room temperature. For example: coal, camphor, wood, charcoal etc. 

2. Liquid Fuels: Volatile liquids which produce combustible vapour are called liquid fuels. These are widely used fuels in our vehicles. For example Petrol, kerosene, diesel etc. 

3. Gaseous Fuels: Combustible gases or a mixture of combustible gases are called gaseous fuels. For example: CNG, LPG, propane, biogas etc. 

Harmful Effects of Burning of Fuels: 

1. Fuels containing carbon like wood, coal or any fossil fuel release unburnt carbon particles (called suits). These are dangerous pollutants that cause respiratory diseases, such as asthma or even cancer. 

2. Incomplete combustion of carbon fuels gives carbon monoxide which is a poisonous gas and prolonged exposure can be fatal.

3. Increased concentration of carbon dioxide in the air which is called greenhouse gas is causing global warming.

4. Oxides of Sulphur and nitrogen dissolve in rainwater and form acids. Such rain is called acid rain. It is very harmful to crops, buildings and soil as it increases the acidity of the soil and corrodes the metal surface faster.

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A Brief Overview of A Few Topics Covered In Class 8 Science Chapter 6

Combustion

Combustion is defined as the chemical process in which substances with oxygen take place to give off light and heat. 

E.g., burning wood

Combustible Substances

Combustible substances are defined as those that can easily catch fire. 

E.g., paper, wood, etc. 

For combustion to take place, the presence of oxygen is essential. 

Non-Combustible Substances

Non-combustible substances are defined as those that do not readily catch fire. 

E.g., water, sand, etc. 

Fuels

Fuels are defined as those substances which produce energy on combustion. E.g., fossil fuel, nuclear energy, etc.

Fuels are obtained in the form of solid, liquid, or gas. 

They can be obtained both naturally or artificially. 

Ignition Temperature

It is the minimum temperature at which a particular substance catches fire. 

Inflammable Substances

These are substances with low ignition temperatures and can easily catch fire. 

E.g., acetone, diesel, etc. 

Fire

Fire is the result of a chemical combustion reaction taking place between fuel and oxygen. The fire lasts depending on the amount of fuel and oxygen available. 

Fire Triangle

To generate fire, there is a requirement of three things majorly:

• Fuel or combustible substance

• The heat source helps in increasing the ignition temperature

• Ample oxygen helps in sustaining the combustion

In case any of these elements are removed, fire can be controlled.

Candle Flame

The visible part of the fire, which contains gases, is called flame. 

Zones of Candle Flame

The outer zone of flame undergoes complete combustion and is the hottest part of the flame. It is blue. It is non-luminous. 

The middle zone of flame undergoes partial combustion and is moderately hot. It is the brightest part.

The innermost zone contains unburnt wax vapors and is black in color. 

Smoke

It is the unburnt particles present in solid form dispersed in the air. 

The black color appears due to the unburnt carbon particles in the smoke. 

Types of Combustion

Rapid combustion happens when both the heat and light are released in a brief period. 

E.g., LPG combustion.

Spontaneous combustion happens when substances catch fire spontaneously without any heat and happen on their own. E.g., forest fires.

Calorific Value of Fuel

Calorific value is the amount of heat energy production when complete combustion of 1kg of fuel occurs. The expression for calorific value is kilojoule/kg (kJ/kg).

Efficiency of Fuel

Efficiency is the energy released in a fuel combustion process converted into practical work.

Key Features of Class 8 Science Chapter 6 Revision Notes

• CBSE Class 8 Science Chapter, 6 revision notes are provided for free pdf download.

• Our subject experts prepare these revision notes after extensive research of the topics.

• The important points of the chapter are summarised in pointers to assure proper understanding of concepts.

• These revision notes are extremely helpful for preparing for the Class 8 Science exam and other competitive exams like Olympiad.

• Few concepts are explained with well-illustrate diagrams to help students understand the topic in a better way.

How To Score Good Grades In Class 8 Science Exam?

Students can easily score good grades in the Class 8 Science exam if they:

• Understand and learn all the topics covered in the Class 8 Science syllabus.

• Write while learning the topics. This process helps them to retain the concepts in their brain for a longer period.

• Revise timely without taking a long break.

• Understand concepts and attempt text series to analyze the preparation level.

Important Questions For Practice

Very Short Answer Type Questions

1. What is combustion?

2. What is known as ignition temperature?

3. What is an explosion?

4. What is rapid combustion?

5. Define caloric value.

Short Answer Type Questions

1. Explain the process of acid rain.

2. What is global warmimg?

3. Explain the two different types of combustion.

4. What are inflammable substances?

5. How carbon-di-oxide helps to control fires.

Long Answer Type Questions

1. Explain the structure of a flame.

2. How can we best control fire?

3. What harmful effects are caused to the environment due to an increase in fuel consumption?

Significance of Revision Notes for CBSE Class 8 Science Chapter 6 - Combustion and Flame

The significance of having well-structured revision notes for CBSE Class 8 Science Chapter 6, "Combustion and Flame," cannot be overstated. These notes condense the chapter's vast information into a concise format, making it easier for students to review and retain crucial concepts. Firstly, they offer a clear and organized overview of the topic, helping students grasp the intricate details of combustion processes, types of flames, and fire safety measures. Secondly, revision notes enhance time management during exam preparation, enabling students to allocate their study time effectively. They also serve as quick reference guides, allowing students to find specific information swiftly. Ultimately, revision notes foster better comprehension and retention, making the study of combustion and flame more manageable and contributing to academic success.

Conclusion

Class 8 Science Chapter 6 notes provide students with a helping hand when preparing a few days before the exams. Here, students can find the explanation of all the topics covered in the chapter in an easy-to-understand format. The information in notes is systematically arranged for the student's convenience. Download the pdf and ace your exam preparation.