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Thermodynamics Chemistry

  1. Nov 17, 2014 #1
    1. The problem statement, all variables and given/known data
    How much energy is required to decompose 765 g of PCl3, according to the reaction below? The molar mass of PCl3 is 137.32 g/mol and may be useful.

    4 PCl3(g) → P4(s) + 6 Cl2(g) ΔH°rxn = +1207 kJ

    3. The attempt at a solution

    765 g PCl3 x 4 mol PCl3/137.32 g PCl3 = 22.28 mol PCl3

    22.28 mol PCL3 x 1207 kJ/4 mol PCl3 = 6.72 x 103 kJ

    Which is incorrect...


    I converted from grams to mols then i converted mols to kJ, which did not give me the correct answer.
    Im probably using a wrong sign somewhere or completely approaching the problem correctly.

    Thank you for your help
     
  2. jcsd
  3. Nov 17, 2014 #2

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    The highlighted operators are incorrect. Pay attention to number of moles in the equation for enthalpy.
     
  4. Nov 17, 2014 #3
    the number of moles is 4? I got 4 from the balanced equation?


    could you explain more on what I'm doing wrong?
     
  5. Nov 17, 2014 #4

    Bystander

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    Step at a time: PCL3 is 137.32 gram per mole (gram mole, gram molecular weight), also written 137.32 g/mol. How many moles in 765 g?
     
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