Classifying Organic Reactions (Edexcel IGCSE Chemistry)

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Classifying organic reactions

  • The reactions of organic compounds can be classified into
    • Substitution
    • Addition
    • 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
      • This is termed complete combustion

CH4   +   2O2   →   CO2   +   2H2O

C3H8   +   5O2   →   3CO2   +   4H2O

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

CH4   +   begin mathsize 14px style bevelled bold 3 over bold 2 end styleO2   →   CO   +   2H2O

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Stewart

Author: Stewart

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Stewart has been an enthusiastic GCSE, IGCSE, A Level and IB teacher for more than 30 years in the UK as well as overseas, and has also been an examiner for IB and A Level. As a long-standing Head of Science, Stewart brings a wealth of experience to creating Exam Questions and revision materials for Save My Exams. Stewart specialises in Chemistry, but has also taught Physics and Environmental Systems and Societies.