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Chapter - 6, Combustion and Flame, Science, Class 8
The document discusses the process of combustion, types of fuels, and their effects on the environment. It details different types of combustion, such as slow, rapid, spontaneous, and explosive, and the conditions necessary for combustion to occur. Additionally, it addresses the environmental impacts of burning fossil fuels, including global warming and acid rain, and describes measures like fire extinguishers to manage combustion.
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Chapter - 6, Combustion and Flame, Science, Class 8
- 1. CHAPTER – 6 COMBUSTIONAND FLAME Email for more PPTs at a very reasonable price. Email: [email protected]
- 2. INTRODUCTION • We usedifferent kinds of fuel for various purposes at home, in industry and for running automobiles. • The materials which produce heat energy on burning in air are called fuels.
- 3. COMBUSTION AND ITS TYPES Whatis combustion ? • The process of production of heat and light by the burning of a combustible substance in the presence of air is called combustion. e.g. magnesium burn to form magnesium oxide and produces a dazzling white flame and a large amount of heat energy.
- 4. Substance Combustible E.g. wood, paper, magnesium, Keroseneoil, charcoal etc. Non-Combustible E.g. Iron nails, Stone piece, Glass etc.
- 5. IGNITION TEMPERATURE / KINDLINGTEMPERATURE “The lowest temperature at which a substance catches fire is called its ignition temperature”. E.g. Ignition temperature of phosphorous is 35oC. So unless the phosphorous is heated to 35oC, it will not catch fire. However if temperature of air is 35oC or more, phosphorous will catch fire without heating.
- 6. INFLAMMABLE SUBSTANCES • Thesubstances which have very low ignition temperature and can easily catch fire with a flame are called inflammable substance. e.g. Petrol, alcohol, LPG etc., have low ignition temperatures. • Ignition temperature of inflammable substances is generally less than 100oC. Excess supply of supporter of combustion leads to complete combustion.
- 7. CONDITIONS NECESSARY FORCOMBUSTION There must be a combustible substance. There must be a continues supply of oxygen or air. The temperature of combustible material should be above its ignition temperature.
- 8. SOURCE OF SOLAR ENERGY •Sun neither use conventional combustible materials nor does it use oxygen or air as supported combustion. • The 98% mass of sun is made of hydrogen which is at very high temperature. • At this high temperature hydrogen atoms fused in one another to form helium atoms.
- 9. TYPES OF COMBUSTION There arefour types of combustion a) Slow combustion b) Rapid Combustion c) Spontaneous Combustion d) Explosive Combustion
- 10. SLOW COMBUSTION • Whena combustible material burns at a slow or moderate rate, it is called slow combustion. • During slow combustion there is not sufficient supply of air, thus, combustion is never complete and as a result more or harmful gases are formed. e.g. cow-dung cakes, wood, kerosene oil lamp.
- 11. RAPID COMBUSTION • When acombustible material (generally gas) burns rapidly to produce heat and light, it is called rapid combustion. e.g. LPG and CNG, magnesium ribbon, match stick, dry grass etc. • During rapid combustion, there is sufficient supply of air and hence the combustion is complete.
- 12. SPONTANEOUS COMBUSTION • The combustionin which a material suddenly bursts into flames, without the application of any apparent cause is called spontaneous combustion or combustion that occurs without the aid of any external heat is known as spontaneous combustion. • When a small piece of phosphorous or sodium is kept in air for some time, it suddenly burst into flames.
- 13. • These materialsinitially form their oxides and produce heat energy which increases the temperature above ignition temperature and they suddenly burst into flame. • Forest fires are also the result of spontaneous combustion because there is a combustible material, a supporter of combustion and the right ignition temperature.
- 14. EXPLOSIVE COMBUSTION • When amixture of combustible material and air completely burns in a very short span of time in same closed space, explosion combustion takes place. • When a sudden reaction takes place with the evolution of heat, light and a large amount of gas formed in the reaction is liberated is called explosion. • Examples: Bursting of crackers, shot of a gun etc.
- 15. • Explosion canalso take place if pressure is applied on the cracker. • During explosive combustion, generally there is internal supply of oxygen or air.
- 16. FIRE EXTINGUISHER • Thejob of fire extinguishers is to cut off the supply of air to bring down the temperature of the fuel or both. • One of the most common fire extinguisher is Soda Acid. • Water is the most common fire extinguisher for wood or paper.
- 17. • Combustion ofmost fuels releases carbon dioxide in the environment. Increased concentration of carbon dioxide in the air is believed to cause Global Warming. It happens due to rise in temperature of the atmosphere of the earth, melting of polar glaciers, which leads to rise in the sea level causing floods in the coastal area. • Burning of coal and diesel releases Sulphur dioxide gas. It is an extremely suffocating and corrosive gas.
- 18. • Petrol enginesgive off gaseous oxides of nitrogen. • Oxides of Sulphur and nitrogen dissolve in rain water and from acids. Such rain is called Acid Rain. It is very harmful for crops, buildings and soil. • Now use of diesel and petrol is replaced by Compressed Natural Gas (CNG) because it produces the harmful product in very small amount and is a cleanser fuel.
- 19. FLAMES • A regionof burning gases is called flame. • A flame is a zone where the burning of gases or vapour takes place with the production of light and heat. A flame results due to rapid combustions of fuel.
- 20. FUELS AND THEIRTYPES “Any substance which is easily available cheaper and burns in air at a moderate rate, producing a large amount of heat energy, without leaving behind any undesirable residue is called a fuel”.
- 21. FUEL EFFICIENCY • Different typesof fuels have different efficiency, which is measured in their calorific value. • Fuel may be categorized on the basis of their individual calorific value.
- 23. GLOBAL WARMING • The CO2in air traps the heat of the sun radiated back by the earth. This makes the air warm and comfortable for living beings and in-fact makes it possible for life on earth to exist.
- 24. EFFECT OF GLOBAL WARMING • Scientistsbelieve that the average global temperature may rise as much as 2oC by the end of the century. • This can cause large scale melting of ice in the polar regions and also expansion of ocean water.
- 25. ACID RAIN • Sulphuris present in coal as an impurity. When coal is burnt in homes, factories or power plants Sulphur dioxide is given off. Sulphur dioxide is poisonous, it affects our lungs. • It combines with the oxygen in the air to form Sulphur trioxide (SO3). This reacts with water in the clouds to form Sulphuric acid (H2SO4).
- 26. EFFECT OF ACID RAIN •The water of lakes and rivers becomes acidic and thus unsuitable for aquatic plants and animals. • The soil becomes acidic and therefore unsuitable for cultivation. • Sculptures, monuments and buildings are eroded.
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