COMBUSTION AND FLAME Fuel: Combustible substance which provides energy on burning in air. Fuel may be solid, liquid or gaseous. Solid fuels: Wood, coal, cowdung, charcoal, etc. Liquid fuels: kerosene, petrol, diesel, etc. Gaseous fuels: Compressed Natural Gas(CNG), liquid Petroleum Gas(LPG), Coal gas, etc. Combustion is a chemical process in which a combustible substance reacts with oxygen to give off energy in the form of heat and light. Magnesium (Mg) burns to form Magnesium oxide (MO) and produces heat and light Burning of charcoal in air produce carbon dioxide (CO2), heat and light. In the sun, heat and light are produced by nuclear reaction. Ignition temperature is the lowest temperature at which a substance catches fire. Below ignition temperature, a substance can’t catch fire. Conditions required to produce fire: Fuel, air (Oxygen) and heat (to raise ignition temperature). Inflammable substances are substances which have very low ignition temperature and can easily catches fire with flame. Examples: Alcohol, petrol, LPG, etc. Early matchsticks were made of mixture of antimony trisulphide, potassium chlorate and white phosphorus with some glue and starch. Modern matchstick head is made by potassium chlorate and trisulphide. Rubbing surface of match stick is made of powdered glass and little red phosphorus. When head of the match stick is rubbed against rubbing surface, red phosphorus in rubbing surface get converted into white phosphorus which reacts with Potassium chlorate in head in order to generate enough heat to ignite antimony trisulphide and start combustion. Water lowers ignition temperature to prevent fire from spreading. Water vapour cut air supply and extinguishes fire. Water extinguishes fire of burning wood ad paper. Water is not suitable for fires involving oil, petrol and electricity. Carbondioxide (CO2) extinguisher suits best for electrical equipment and inflammable materials like petrol. CO2 is heavier than oxygen, covers the fire like a blanket and cuts oxygen. Carbondioxide has least harm to electrical equipments. Sodium bicarbonate/baking soda and potassium bicarbonate powder are source of CO2 i.e. release CO2. TYPES OF COMBUSTION Rapid combustion is a type of combustion where combustible substance like gas burns rapidly and produces heat and light. Spontaneous combustion is a type of combustion in which a material suddenly burst into flames, without application of any apparent cause. Example: Burning of phosphorus in air at room temperature, burning of coal dust, etc. Explosion is a sudden reaction where large amount of gas is liberated along with heat, light and sound. Example: Cracking of fire crackers. FLAME Substance which vapourise during burning gives flame. Unburnt carbon particles deposits as black coloured substances on burning FUEL Ideal fuel is one which is readily available, cheap, burns easily in air at moderate rate and produces a large amount of heat. It does not leave behind any undesirable substances. Calorific value is the amount of heat energy produced on complete combustion of 1 kg of a fuel. It is expressed in Kilojoule per kg(KJ/Kg). BURNING OF FUELS LEAD TO HARMFUL PRODUCTS Increasing fuel consumption has following harmful effect; 1) Cause disease and pollute environment: Carbon fuels like wood, coal, petroleum release unburnt carbon particles which are pollutants and cause respiratory disease like asthma. 2) Produce Carbon monoxide gas: Incomplete combustion of these fuels gives carbon monoxide gas which is very poisonous gas which may kill the person inhaling it. 3) Cause Global Warming: Combustion of most fuels releases carbon dioxide in environment which may finally cause global warming. Global warming is rise in temperature of atmosphere of earth resulting in melting of polar glacier leading to rise in sea level, causing floods in the coastal areas. Low lying coastal areas may even be permanently submerged under water. 4) Acid rain: Burning of coal and diesel release sulphur dioxide gas. It is an extremely suffocating and corrosive gas. Oxides of nitrogen are produced by petrol engines. Oxides of nitrogen and sulphur dissolve with rain water to form acid rain which is very harmful for crops, buildings and soil. Use of petrol and diesel as fuels in automobiles is replaced by CNG(Compressed Natural Gas) because CNG produce less harmful products.
CELL ORGANELLES
STRUCTURE OF NUCLEUS
CHLOROPLAST
MITOCHONDRIA