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More Entropy

  1. Nov 28, 2008 #1

    a.a

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    1. The problem statement, all variables and given/known data

    Cyclohexanol has a heat of vaporization of 54 kJ/mol and the absolute entropies of the liquid and gas are 200 and 328 J/K-mol, respectively. Which of the following is false?


    a. The entropy of vaporization is positive.

    b. The heat of formation of liquid cyclohexanol is less than that of the vapour.

    c. At 80oC the free energy change for the vaporization is negative.

    d. At the boiling point the free energy change for vaporization is zero.

    e. At 80oC, cyclohexanol vapour spontaneously condenses into a liquid.


    2. Relevant equations

    delta G = delta H - TdeltaS

    3. The attempt at a solution

    I know statements a, b, and d are true for all substances, so they are not false.

    I calculated deltaG at 80degrees and got -45203146 KJ/mol, but that seems a little tp big. I cant figure out where I'm going wrong...

    deltaG= 54 Kj/mol - (80 + 273.15 K)(128 J/Kmol)
    = 54 KJ/mol- (353.15)(128000KJ/mol)
    = -45203146 KJ/mol
     
  2. jcsd
  3. Nov 28, 2008 #2

    a.a

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    Oh, wow... I can't belive I made this mistake... hope it doesn't happen agian; exams are comming up.

    I converted to KJ wrong, it should be 128J= 0.128KJ,
    and that would make deltaG = + 8.797

    So that means that statement c is false. :)
     
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