Physical and Chemical Changes


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 Physical changes are the change, which only affect the physical properties like colour, hardness, density, melting point etc. of matter, but do not affect the composition and chemical properties of matter.

 A physical change is temporary, while a chemical change is permanent.


 Crystallisation, sublimation, ‘boiling, melting, vaporisation, cutting of trees, dissolving sugar or salt in water etc. are physical changes.

 Chemical changes affect the composition as well as chemical properties of matter and result in the formation of a new substance

 Burning of fuel, burning of candle and paper, electrolysis of water, photosynthesis, ripening of fruits etc, are examples of chemical changes


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Coal
Coal is obtained by carbonization of vegetable matter and is available in different varieties:

 Peat- 60% C  Lignite or Brown Coal – 70% C  Bituminous – 60 to 80 % C  Anthracite Coal – 90% C


TRICK to Remember Coal Varities is PLBA ( carbon content increasing from peat to anthracite)


FLAME
Flame contains three parts


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1. Innermost Part- which is black due to the presence of unburned carbon particles- has lowest temperature.

2. Middle part – is yellow due to incomplete combustion of fuel.


3. Outermost part- which is blue due to complete combustion of fuel is the hottest and used by goldsmith to heat the gold.




Fire Extinguishers

 Water extinguishes fire because as it evaporates, the vapours surround the burning substance,


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cutting off the oxygen supply, thus inhibiting burning process.

 In case of electrical or oil (petrol) fires, water cannot be used as extinguisher.

This is because water is a conductor of electricity and heavier than oil. Thus, oil floats over it and continues to burn.  Carbon dioxide, which is generated by the reaction of baking soda with acid, is used for electrical or oil fires.

# Quality of petrol is measured in terms of octane number and that of diesel in terms of cetane number.

Safety Matches

The match heads contain sulfur (sometimes antimony trisulfide)


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and oxidizing agents (usually potassium chlorate), with powdered glass, colorants, fillers, and a binder made of glue and starch.

The striking surface consists of powdered glass or silica (sand), red phosphorus, binder, and filler