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    Struggling with this summary question in my textbook about bond enthalpy:
    The difference between the enthalpy change of combustion of successive straight chain alkanes is around -650kJmol-1. This is because each alkane differs from the previous one by a methyl fragment, -CH2.
    a. Write an equation for the combustion of one of the carbon and two hydrogen atoms in this fragment.
    I've done this and my answer is correct, its CH2 + 1/2O2 → CO2 + H2O.
    b. Use bond enthalpies to calculate a value for the enthalpy change of the reaction in part a (including the breaking of the C-C bond).
    The answer in the back of the book says -618kJmol-1, but I've managed to work it out to -1116kJmol-1 and have no idea how you get to -618.

    Help will be much appreciated!!!!!
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    (Original post by uselessdoctor)
    Struggling with this summary question in my textbook about bond enthalpy:
    The difference between the enthalpy change of combustion of successive straight chain alkanes is around -650kJmol-1. This is because each alkane differs from the previous one by a methyl fragment, -CH2.
    a. Write an equation for the combustion of one of the carbon and two hydrogen atoms in this fragment.
    I've done this and my answer is correct, its CH2 + 1/2O2 → CO2 + H2O.
    b. Use bond enthalpies to calculate a value for the enthalpy change of the reaction in part a (including the breaking of the C-C bond).
    The answer in the back of the book says -618kJmol-1, but I've managed to work it out to -1116kJmol-1 and have no idea how you get to -618.

    Help will be much appreciated!!!!!


    Your answer is not correct - the equation you have given is not balanced!.
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    (Original post by charco)
    Your answer is not correct - the equation you have given is not balanced!.
    What a stupid mistake haha, I completely missed the 1 1/2 in the answers and just read it as 1/2. Balancing equations - not my strong point. Thanks!
 
 
 
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