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Calculate resonance energy

  1. Oct 16, 2012 #1

    utkarshakash

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    1. The problem statement, all variables and given/known data
    Determine the resonance energy of gaseous benzene from the following data
    [itex]ΔH^{o}_{diss}(H,g)=435.9kJmol^{-1}, ΔH^{o}_{sub} C_{graphite}=718.4kJmol^{-1}
    ΔH^{o}_{f} Benzene(g)=82.9kJmol^{-1}[/itex]

    [itex]ε_{C-H}=416.3kJmol^{-1},ε_{C-C}=331.4kJmol^{-1},ε_{C=C}=591.3kJmol^{-1}[/itex]

    2. Relevant equations

    3. The attempt at a solution
    I have the following reaction

    [itex]6C+3H_{2} \rightarrow C_{6}H_{6}[/itex]

    To calculate ΔH
    [itex]\left[ 6 \times ΔH^{o}_{sub} C_{graphite} + 6 \times ΔH^{o}_{diss}(H,g) \right] - \left[ 6 \times ε_{C-H} + 3 \times ε_{C-C} + 3 \times ε_{C=C} \right][/itex]

    Now resonance energy can be calculated by
    [itex]R.E. = ΔH_{observed}-ΔH_{calculated}[/itex]

    Substituting the values does not give me the correct answer.
     
  2. jcsd
  3. Oct 16, 2012 #2

    AGNuke

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    To calculate ΔH
    [itex]\left[ 6 \times ΔH^{o}_{sub} C_{graphite} + 3 \times ΔH^{o}_{diss}(H,g) \right] - \left[ 6 \times ε_{C-H} + 3 \times ε_{C-C} + 3 \times ε_{C=C} \right][/itex]

    I believe you are dissociating 3 H-H bonds.
     
  4. Oct 16, 2012 #3

    utkarshakash

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    OK So I got my answer(not exactly but very close) but the answer given in my book is positive unlike mine.
     
  5. Oct 17, 2012 #4

    AGNuke

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    Its because you did mistake there again.

    R.E. = H(calculated) - H(observed)
     
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