Chemistry – Combustion And Flame – Notes For W.B.C.S Examination.
রসায়ন – দহন এবং শিখা – WBCS পরীক্ষার জন্য নোট।
- A chemical process in which a substance reacts with oxygen and give off heat is known as combustion.Continue Reading Chemistry – Combustion And Flame – Notes For W.B.C.S Examination.
- The substance that undergoes combustion is called as combustible or fuel.
- The fuel can be in the form of solid, liquid, or gas.
- During the combustion, light is also given off either in the form of a flame or as a glow.
- The substances which vaporize during burning time, give flames.
- There are three different zones of a flame dark zone, luminous zone and non-luminous zone.
- Different substances catch fire at different temperatures.
- The lowest temperature at which a substance catches fire is known as its ignition temperature.
- A match contains antimony trisulphide and potassium chlorate.
- The rubbing surface of match contains powdered glass and a little red phosphorus.
- Red phosphorus is much less dangerous.
- When the match stick is struck against the rubbing surface, some red phosphorus gets converted into white phosphorus; the process immediately reacts with potassium chlorate present in the matchstick head and produce enough heat to ignite antimony trisulphide; likewise, combustion starts.
- The substances, which have very low ignition temperature and can easily catch fire with a flame, are known as inflammable substances. E. g. petrol, alcohol, Liquified Petroleum Gas (LPG), etc.
Fire Extinguisher
- Water is the most common fire extinguisher.
- Water, as fire extinguisher, works only when things like wood and paper are on fire.
- If electrical equipment is on fire, water may conduct electricity and damage those trying to douse the fire.
- Water is also not a good extinguisher for fires involving oil and petrol.
- For fires that involve electrical equipment and inflammable materials such as petrol, Carbon Dioxide (CO2) is the best extinguisher.
- One of the ways to get CO2 is to release plenty of dry powder of chemicals such as sodium bicarbonate (baking soda) or potassium bicarbonate.
- Phosphorus burns in air at room temperature.
- The amount of heat energy produced on complete combustion of 1 kg of a fuel is known as its calorific value.
- The calorific value of a fuel is measured in a unit called kilojoule per kg (kJ/kg).
- The following table illustrates the Calorific Values of Different Fuels −
Fuel | Calorific Value (kJ/kg) |
---|---|
Cow dung cake | 6000-8000 |
Wood | 17000-22000 |
Coal | 25000-33000 |
Petrol | 45000 |
Kerosene | 45000 |
Diesel | 45000 |
Methane | 50000 |
CNG | 50000 |
LPG | 55000 |
Biogas | 35000-40000 |
Hydrogen | 150000 |
- Combustion of most fuels releases carbon dioxide in the environment.
- Increased concentration of carbon dioxide in the air is most likely causes global warming.
- The rise in temperature of the atmosphere of the earth is known as Global Warming.
- Global warming causes melting of polar glaciers, which leads to a rise in the sea level that ultimately causing floods in the coastal regions.
- Oxides of sulphur and nitrogen dissolve in rain water and form acids; such type of rain is known as acid rain.
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