CHEMISTRY OF ETHENE
 
 
 
INTRODUCTION
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   Molecular formula = C2H4
   Empirical formula = CH2
   Molecular mass = 28
   Empirical mass = 14
   Homologous series = alkene
STRUCTURE OF ETHENE
 
   COMPOSITION OF EHTHENE:
   Ethene molecule consists of two carbon atoms and four H-atoms. i.e.    CH2=CH2
METHODS OF PREPARATION
 
   BY VICINAL DIHALIDE:
   When vicinal dihalide is heated with zinc dust, two halide atoms are removed from the compound and    ethene is formed.
            CH2-CH2 + Zn CH2=CH2 + ZnCl2
              |       |
              Cl     Cl
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   BY THE REDUCTION OF ETHYNE:
   Under control conditions ethyne adds two H-atoms to form ethene in the presence of Nickel(Ni) at    200oC.
             + H2  H-C=C-H
                  
   BY THE DEHYDROHALOGENATION OF ALKYL HALIDE:
   When alkyl halide (ethyl chloride) is treated with alcoholic KOH, b-elimination takes place and ethene is    obtained.
            CH3-CH2Cl + KOH CH2=CH2 + KCl + H2O
   BY THE DEHYDRATION OF ALCOHOL:
   When ethyl alcohol is heated with conc.H2SO4 at 170oC, dehydration of alcohol takes place and    ethene is formed.
            C2H5OH C2H4 + H2O
                      OR
   Ethyl alcohol may also be converted into ethene by passing vapours of ethyl alcohol over catalyst    (Al2O3, H3PO4/Al2O3).The reaction is carried out at 350C in the presence of Al2O3 and at 250C when    H3PO4/Al2O3 is used.
            C2H5OH C2H4 + H2O
CHEMICAL PROPERTIES
 
   ADDITION REACTIONS OF ETHENE:
   ADDITION OF CHLORINE:
            CH2=CH2 + Cl2 CH2Cl-CH2Cl (1,2-dichloroethane)
   ADDITION OF BROMINE:
            CH2=CH2 +Br2 CH2Br-CH2Br (1,2-dibromoethane)
   ADDITION OF IODINE:
            CH2=CH2 + I2 CH2I-CH2I (1,2-diiodoethane)
   ADDITION OF HYDROGEN:
   When a mixture of ethene and hydrogen is passed over finely divided nickel, hydrogen is added to    ethene with the formation of ethane.
            CH2=CH2 + H2 CH3-CH3
   ADDITION OF H2O:
            CH2=CH2 + HOH CH3-CH2-OH
   ADDITION OF HCl:
            CH2=CH2 + HCl CH3-CH2-Cl
   COMBUSTION REACTION:
            CH2=CH2 + 3O2 2CO2 + 2H2O
PHYSICAL PROPERTIES
 
Ethene is a colourless gas with very light sweetish smell.
It has melting point -169oC.
It has boiling point -104oC.
It is insoluble in water but soluble in alcohol and ether.
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