Combustion and flame

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Combustion and flame

  1. 1.  The process of burning of substances in air with the release of heat and light is called combustion.
  2. 2.  A substance that Burns in air to produce heat and light is called  Eg: Wood, Petrol
  3. 3.  A substance that does not burn in air is called a  Eg: Stone, Metal
  4. 4.  During combustion substances like coal or charcoal react with oxygen in air to form carbon dioxide.  Carbon + Oxygen= Carbon dioxide + Heat  Hydrogen reacts with oxygen to form water.  Hydrogen + Oxygen = Water + Heat  Methane reacts with oxygen which burns to produce carbon dioxide and water.  Methane + Oxygen = Carbon dioxide + Water + Heat
  5. 5.  Combustion takes place only if there is  Combustible Substance  Air( Oxygen)  Temperature
  6. 6.  A substance has to heated to a certain minimum temperature before it can catch a fire. This temperature is different in different objects. In petroleum the ignition temperature is very less.  The minimum temperature at which a substance catches fire is called its ignition temperature.
  7. 7.  http://www.youtube.com/watch?v=9d6tseOh 21Y  http://videos.howstuffworks.com/discovery/ 29392-assignment-discovery-combustion- video.htm
  8. 8.  Rapid combustion – occurs when a substance burns rapidly to produce heat and light. Ex- LPG , paper , wick of an oil lamp.  Spontaneous combustion – occurs when a substance starts burning suddenly even without being heated. Ex- white phosphorus whose ignition temperature is 35°C  Explosion – is a combustion reaction that occurs suddenly when a material is heated liberating a large amount of heat , light and sound.Ex- firecrackers.
  9. 9.  An uncontrolled fire can be disastrous – it can destroy life and property in minutes.  For the prevention of an uncontrolled fire each city has fire stations equipped with fire-fighting equipment . Water and fire extinguishers are used to put out fires.
  10. 10. . Remove the combustible material. . Reduce temperature to the ignition temperature of the combustible substance. . Cut off air supply.
  11. 11.  Dry powder fire extinguisher – it contains baking soda (NaHCO3).When this mixture is thrown over a fire , baking soda decomposes to release carbon di oxide which extinguishes the fire.  Soda-acid fire extinguisher – it consists of a small glass bottle filled with sulphuric acid that is supported in a strong iron vessel containing sodium bicarbonate. On striking the knob, the bottle containing acid breaks and carbon di oxide is liberated by the action of the acid on baking soda.
  12. 12.  Foam fire extinguisher – in this a solution of aluminium is taken in the glass bottle instead of sulphuric acid. It releases a foam of carbon di oxide that surround the burning substance and cuts off its air supply. This type of fire extinguisher is especially used to extinguish oil fires.
  13. 13.  http://www.youtube.com/watch?v=uUpuR4 BoAzQ
  14. 14. Combustible materials such as wood,coal,gas or oil which are burnt to produce heat or power are known as fuels.  Solid fuels are easy to store but difficult to use.  Gaseous fuels are difficult to store; they have to be compressed at high pressures and are stored in sealed cylinders or tankers. These can be dangerous if a leak develops because the fuel can spread very fast. However gaseous fuels are easy to use.  Liquid fuels can be stored easily and are easy to use.
  15. 15. calorific value of fuel. note: the higher the calorific value the better the fuel. joule per kilogram kilojoule per kilogram
  16. 16.  It should have a high calorific value.  It ignition temperature should be neither too low nor too high.  It should be cheap and readily available.  It should be easy and safe to transport, handle and store.  It should not cause air pollution upon burning.  It should not leave behind solid residue upon burning. No fuel really meets all the characteristics listed here. Natural gas is the closest to an ideal fuel. Considerable research is being done to produce efficient fuel cells that use hydrogen and oxygen to produce electricity.
  17. 17. Carbon monoxide and soot are also produced during the combustion of other fuels. They are highly undesirable byproducts of combustion. The fine particles of soot are called suspended particulate matter (spm).They are dangerous pollutants of air and can cause respiratory problems. Some fuels like diesel & coal contain sulphur, which changes to sulphur dioxide (SO2) upon combustion. Engines give out oxides of nitrogen. Both sulphur dioxide and the oxides of Nitrogen are undesirable and harmful byproducts of combustion. Besides being poisonous themselves, they dissolve in rainwater to form acids and cause acid rain.
  18. 18. The carbon dioxide released during combustion can result in an increased percentage of gas in air. An atmosphere with excess carbon dioxide traps more heat- this is called greenhouse effect. Many scientists believe that this can result in the average temperature of the earth. This phenomenon is called global warming. Global warming can lead to the melting of polar ice causing flooding of low lying costal lands and also cause climate changes.
  19. 19.  https://www.youtube.com/watch? v=dP- tg4atr5M&feature=player_detailpage
  20. 20.  The process of burning of substances in air with the evolution of heat and light is known as combustion.  A substance that burns in air to produce heat and light is called a combustible substance. A substance that does not burn in air is called a non-combustible.  The conditions that must be met for combustion are: presence of a combustible substance, presence of oxygen(air) and attainment of ignition temperature.  The minimum temperature at which a substance catches fire is called it’s ignition temperature.  The three types of combustion are rapid combustion, spontaneous combustion and explosion.
  21. 21.  A fire can be extinguished by removing the combustible substance, reducing the temperature to below the ignition temperature or by cutting out the air supply.  Fire extinguishers mainly use carbon dioxide to extinguish fires.  The important criteria for the selection of a fuel are physical state, calorific value, ignition temperature, combustion residue, emissions and cost.  The candle flame has four zones dark zone, luminous zone, non luminous zone and blue zone.  The luminous zone produces light due to the glowing of carbon particles. The non-luminous zone is the hottest.
  22. 22.  Calorific value of a fuel an be defined as the amount of heat liberated when one kilo-gram of the fuel is completely burnt in an sufficient supply of oxygen.  Natural gas is the closest to an ideal fuel.  Some harmful substances given off during combustion are suspended particulate matter (SPM), carbon dioxide, carbon monoxide, sulphur dioxide and oxides of nitrogen.
  23. 23. 1.The chemical reaction in which a fuel is burned to release heat energy is called __________ . Ans. Combustion 2.Wood, paper, kerosene and LPG are examples of ________ . Ans. Combustible substances 3.The _________ temperature is the minimum temperature at which a fuel can catch fire. 4.Combustion of wood can be classified as __________ combustion. Ans. Rapid 5.A soda-acid type fire extinguisher gives out _________ to extinguish a fire. Ans. Carbon dioxide 6._________ extinguisher is used to extinguish a fire. Ans. Foam fire
  24. 24. 7.The zone that produces light in a candle flame is called the _______ zone. Ans. Luminous 8.The amount of heat evolved, in kilojoules, when one kilogram of fuel is burnt completely is called ________ value of the fuel. 9._________ is caused by sulphur dioxide and oxides of nitrogen. Ans. Acid rain 10. ______ _______ can cause flooding of low lying coastal land. Ans. Global warming 11.A substance burnt to obtain heat energy is called a _______ . Ans. Fuel
  25. 25. 12.A foam fire extinguisher gives out a foam of _________ . Ans. Carbon dioxide 13.The glowing ________ particles in the luminous zone of a candle flame make it look yellow. Ans. Unburnt carbon particles.

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