COMBUSTION AND FLAMES

COMBUSTION AND FLAME

 The burning of any substance is considered a chemical change because a new substance is produced along with the change in the chemical structure. (burning means reacting with oxygen)

eg:- burning of magnesium ribbon (where magnesium is converted to magnesium oxide)





COMBUSTION

A chemical process in which a substance reacts with oxygen to produce heat energy is called combustion. During combustion carbon-di-oxide and water is also produced

ie, substance burn + oxygen -----> carbon-di-oxide+ water + heat/light energy

A substance that undergoes combustion is said to be combustible and it is also known as fuel eg:-wood, paper, petrol, kerosene, diesel etc 

A substance which does not undergo combustion is said to be non-combustible. eg:- iron nail, stone, glass etc

NOTE:- Oxygen gas is necessary for the combustion reaction. If oxygen supply is not there means burning doesn't happen or if oxygen supply is insufficient means it will result in the production of carbon-mono-oxide instead of carbon-di-oxide. (carbon-mono-oxide is a poisonous gas)

FOREST FIRE

A distractive fire spread over a forest area or an area of woodland. Reasons for forest fire are natural and man-made like lightning, cigarette, electric spark etc. During summer normally forest fire occurs because of severe dryness of grasses and tree leaves and also due to high temperature and enough supply of air

IGNITION TEMPERATURE

The lowest temperature at which a substance catches fire is called its ignition temperature. The ignition temperature of the different substances is different

  CHEMISTRY OF MATCH STICK

*In ancient time a small piece of pinewood dipped in sulphur were used as a matchstick ( in ancient Egypt). 

*The modern safety matchstick was developed only 200 years ago. Chemicals used in the modern matchsticks are antimoney trisulphide, potassium chlorate and white phosphorus also some glue and starch are applied to the head of the matchstick. When the match stick was struck against a rough surface due to friction heat is produced and the white phosphorus is ignited ( since white phosphorus is dangerous instead of that red phosphorus is used). 

* Nowadays the head of a matchstick contains only antimony trisulphide and potassium chlorate and the rubbing rough surface has powdered glass and a little red phosphorus. when matchstick is struck against a rough surface red phosphorus gets converted to white phosphorus, this immediately reacts with potassium chlorate in the matchstick head to produce enough heat to ignite antimony trisulphide and start combustion

INFLAMMABLE SUBSTANCE

The substance which has very low ignition temperature and can easily catch fire with a flame is called inflammable substances  eg:- LPG, petrol, diesel, kerosene etc

HOW TO CONTROL FIRE

Three essential requirements for producing fire are fuel, the supply of oxygen and heat. so the fire can be controlled by controlling these three factors. That is fire can be extinguished by cutting the supply of the air, bringing down the temperature of the fuel and by eliminating the available fuel.

( Mainly water can be used as a fire extinguisher because it can absorb the heat and evaporate resulting In the reduction of temperature and also the production of water vapour cutting the supply of air. According to the type of fire different types of extinguishers to be used)

TYPE OF COMBUSTION

  • Some materials  can burn rapidly and produce heat and light such combustions are known as RAPIDE COMBUSTION
  • Some materials suddenly burst into flames without any application of any apparent cause is called SPONTANEOUS COMBUSTION
  • For some materials like crackers when ignited, a sudden reaction takes place with the evolution of heat light and sound. A large amount of gas is also liberated such reaction is called EXPLOSION

 FLAME

When a substance undergoes combustion it produces heat along with that flame is also produced(not all the combustion results in flame). The substance which vapourises during burning gives flame. 

eg:- when a candle burns the molten wax rises through the wick vapourised  and produces a flame

If no vapours are produced while burning then there will be no flame, only the substance will become red hot

eg:- when charcoal is burned no flame is produced

STRUCTURE OF THE FLAME


FUEL

Fuel is a source of heat energy that can be used for domestic as well as industrial purposes 

eg:- firewood, petrol, diesel, kerosene etc

CHARACTERISTIC OF A GOOD/IDEAL FUEL

  • Readily available
  • it should be cheap
  • Burn easily in the air at a moderate rate
  • It produces a large amount of heat energy
  • Does not leave behind any undesirable substances
(THERE IS PROBABLY NO FUEL THAT COULD BE CONSIDERED AS AN IDEAL FUEL)

FUEL EFFICIENCY ( CALORIFIC VALUE )

The efficiency of fuel can be expressed in terms of calorific value. The calorific value of a fuel is the amount of heat energy produced on complete combustion of 1 kg of that fuel
unit:-kilojoule per kilogram (kJ/kg)

CALORIFIC VALUE OF DIFFERENT FUELS



HARMFUL EFFECTS OF FUEL CONSUMPTION

Increasing fuel consumption has a lot of harmful effects on the environment

  1. carbon fuels like firewood, charcoal, and petroleum release unburned carbon particles (carbon particles are fine (nano)particles) are dangerous pollutants causing respiratory diseases like asthma
  2. incomplete combustion of fuel resulted in the production of carbon monoxide which is a very poisonous gas (combustion happens with insufficient oxygen supply led to the production of carbon monoxide)
  3. combustion of most fuels releases carbon dioxide, as the amount of carbon dioxide in the atmosphere increases it cause global warming
  4. Byproducts of fuel combustion such as sulphur dioxide, nitrogen dioxide, carbon dioxide etc resulted in acid rain. When coal and diesel burn it produces sulphur dioxide(it is a suffocating and corrosive gas) and the combustion of petrol led to the production of nitrogen dioxide, carbon dioxide is also produced during the combustion of fuels. These oxides of sulphur, nitrogen, and carbon dissolve in rainwater and produce acids such rain is called acid rain
(using firewood as a fuel because of its easy availability and low cost led to deforestation and burning of wood gives a lot of smoke which is harmful to the living beings)

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