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Unit 25. Burning of fuels and fire-fighting. Heat content. Heat content – the total amount of energy stored in a substance. Symbol for the heat content: H. Heat of reaction. Symbol : 

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unit 25

Unit 25

Burning of fuels and fire-fighting

heat content
Heat content
  • Heat content – the total amount of energy stored in a substance.
  • Symbol for the heat content: H
heat of reaction
Heat of reaction
  • Symbol : 
  • The heat of reaction is the difference in the heat content of the products and the heat content of the reactants.
  •  = Hproducts - Hreactants
exothermic reaction1
Exothermic reaction
  • Heat is given out.
  • The total heat content of products is less than the total heat content of reactants.
  • Feeling warm (temperature increases)
endothermic reaction1
Endothermic reaction
  • Heat is absorbed.
  • The total heat content of products is more than the total heat content of reactants.
  • Feeling cold (heat is absorbed and temperature drops.)
fire triangle
Fire Triangle
  • Necessary conditions for burning
  • Fuel – combustible materials
  • Oxidant – usually oxygen from air.
  • Heat – a high enough temperature to start the ignition (burning).
fire fighting
Fire-fighting
  • Remove one or more conditions for putting put fire.
  • e.g., cooling down the fire by spraying cold water.
  • Excluding air (oxidant) by sand / fire-blanket.
  • Cut off the fuel supply.
hill fire
Hill fire
  • Cut down a line of trees in front of the fire.
  • Dig a trench to separate the fire from other trees.
  • Removing fuels.
fire in a cooking pan
Fire in a cooking pan
  • Cover the fire with a lid.
  • For excluding air.
  • Don’t spray water onto the pan. Why ?
  • Oil does not mix water. Spraying water helps to spread the fire.
types of fire
Types of fire
  • Class A – burning ordinary materials such as paper, and wood.
  • Class B – Burning of flammable liquids.
  • Class C – Burning of fiammable gases
  • Class D – Burning metals
fire extinguishers
Fire extinguishers
  • 4 types
  • Water-type fire extinguisher
    • Water fire extinguisher / soda acid fire extinguisher
    • Foam type fire extinguisher
  • Carbon dioxide fire extinguisher
  • Dry powder fire extinguisher
  • Haloform fire extinguisher
water type fire extinguisher1
Water type fire extinguisher
  • Producing a spray of cold water to lower the temperature of fire (to cool the fire)
  • Not for electrical fire
  • For putting fire involving the burning of papers and woods
2 types of water type fire extingusihers
2 types of water type fire extingusihers
  • Water fire extinguisher – forcing a jet of water out when a samll can of compressed carbon dioxide is broken.
  • Soda acid fire extinguisher – carbon dioxide is formed from the reaction of carbonate witrh dilute acid. The building up of pressure forces a jet of water out.
foam fire extinguisher
Foam fire extinguisher
  • Foam keeps the air out.
  • Suitable for putting fire due to flammable liquids.
  • Not suitable for electrical fire.
carbon dioxide fire extinguisher
Carbon dioxide fire extinguisher
  • A denser gas than air, covers the fire and keeps the air out.
  • Used for metal fire and electrical fire.
dry powder fire extinguisher
Dry powder fire extinguisher
  • The powder is solid sodium hydrogencarbonate.
  • Covers the fire and keeps the air out.
  • Decomposes to solid sodium carbonate and carbon dioxide which help to exclude the air.
  • For most fires, including electrical fire.
haloform fire extinguisher
Haloform fire extinguisher
  • BCF ? BTM ?
  • BCF : bromochlorodifluoromethane
  • BTM: Bromotrifluoromethane
  • Volatile and denser than air
  • Forms a blanket over the fire.
  • Keeps the air out and put out the fire.
  • For electrical fire
  • Poisonous vapours
ionic equation for the soda acid fire extinguishers
Ionic equation for the soda acid fire extinguishers
  • CO32-(aq) + 2H+(aq) → CO2(g) + H2O(l)
safety precautions in using gaseous fuels
Safety precautions in using gaseous fuels
  • Why town gas is poisonous?
  • Carbon monoxide, one of the component in town gas, combines with the haemoglobin in red blood cell to form a stable complex – carboxyhaemoglobin which can no longer carries oxygen. Man will be then killed because of lack of oxygen.
  • To keep the room well ventilated (with windows open).
using lpg
Using LPG
  • In limited supply of air’
  • Carbon soot, carbon monoxide and steam are formed.
  • Keep the room well ventilated (with windows open)
fire fighting equipments in the laboratory
Fire-fighting equipments in the laboratory
  • Carbon dioxide fire extinguisher
  • Dry powder fire extinguisher
  • A bucket of sand
  • Fire blanket
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