1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    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


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    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?
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted

Similar Discussions: Thermodynamics Chemistry
  1. In chemistry }}} (Replies: 3)

  2. Chemistry enthalpy (Replies: 5)