EDEXCEL IGCSE CHEMISTRY: DOUBLE SCIENCE 复习笔记:4.1.3 Classifying Organic Reactions

EDEXCEL IGCSE CHEMISTRY: DOUBLE SCIENCE 复习笔记:4.1.3 Classifying Organic Reactions

Classifying Organic Reactions

 

  • The reactions of organic compounds can be classified into substitution, addition and combustion

 

Substitution

  • A substitution reaction takes place when one functional group is replaced by another
    • Example: Methane reacts with bromine under ultraviolet light

     

 

CH4    +    Br2       →            CH3Br   +    HBr

 

    Methane + Bromine   →   Bromomethane + Hydrogen Bromide

Addition

  • An addition reaction takes place when two or more molecules combine to form a larger molecule with no other products
    • Example: Bromine will react with ethene and the bromine molecule will react and add across the double bond of the ethene

     

 

C2H4     +       Br2         →         C2H4Br2

 

Ethene   +   Bromine   →   Dibromoethane

 

 

Combustion

  • This is the scientific term for burning. In a combustion reaction, an organic substance reacts with oxygen to form carbon dioxide (or carbon monoxide if incomplete combustion) and water.
    • Example: Alkenes burn when heated in air of oxygen
    • If there is an unlimited supply of air / oxygen, the products are carbon dioxide and water:

     

 

CH4   +   2O2   →   CO2   +   2H2O

 

C3H8   +   5O2   →   3CO2   +   4H2O

 

  • This is termed complete combustion
    • If there is a limited supply of air / oxygen, the products are carbon monoxide and water:

     

 

CH4   +   ½O2   →   CO   +   2H2O

  • This is termed incomplete combustion

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