Physical And Chemical Change


INTRODUCTION 


Everyday you come across many changes in your surroundings out of these changes some are temporary in nature, while some are permanent in nature and hence these changes are broadly categorised into two types


(i) Physical Changes        
(ii) Chemical Changes

PHYSICAL CHANGES

 (a) Physical changes are those changes which are reversible in nature. 
 (b) These are temparory in nature and also called short duration changes.
 (c) These changes are those in which after the accomplishment of the reaction no new substance is formed. 
 (d) Properties such as shape, size, colour and state are called physical properties any change in these properties of a substance is                 called a physical change.
 (e) For example
 (i) Melting of wax            (ii) Melting of ice        (iii) Evaporation of water
 (iv) Formation of dew            (v) Sublimation of comphor    
 (vi) Crystallization of sugar from its solution
 (vii) Lightning of a bulb

CHEMICAL CHANGES 

  (a) Those changes in which new substances are formed are called chemical changes, the substances changes their identity and get converted into entirely new substance. 
  (b) The new substances usually cannot be reformed back in to their original form, simply these are usually irreversible in nature.
  (c) These changes are parmanent in nature.
  (d) The properties of products are totally different from that of reactants.
  (e) For example
   (i) Burning of candle
   (ii) Burning of fuels (coal, wood, and LPG)
   (iii) Digestion of food
   (iv) Cooking of food
   (v) Formation of curd from milk
   (vi) Decomposition of water into H2 and O2 by passing electricity
         When magnesium wire or ribbon, burn it starts burning with a dazzling white flame.
   (vii) 2Mg + O2 ® 2MgO , MgO + H2O ® Mg(OH)2
   (viii) CuSO4 + Fe ®     FeSO4   + Cu
               Blue             Light green
   (ix) CH3COOH + NaHCO3 ® CH3COONa + CO2 + H2O
           CO2 + Ca(OH)2 ® CaCO3 + H2O
                          white ppt.  

 DURING CHEMICAL CHANGES

(i) Heat, light or any other radiation (ultraviolet for example) may be given off or absorbed
  (ii) Sound production may take place
  (iii) A change in smell may takes place
  (iv) there may be change in the state
  (v) there may be change in the colour
  (vi) evolution of gas may takes place
  (vii) Change in temperature may be observed.
  (viii) Formation of precipitate may be observed.

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