1. Not finding help here? Sign up for a free 30min 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!

Enthalpy Change and Bond Energies

  1. Dec 27, 2015 #1
    1. The problem statement, all variables and given/known data
    upload_2015-12-27_11-25-13.png

    2. Relevant equations


    3. The attempt at a solution
    6C-H bonds= 410 x 6 = 2460 kJ/mol
    3C-C bonds
    H of formation= +53.3 kJ/mol
    H of atomisation = +717 kJ/mol
    H-H = 436 kJ/mol

    as H of formation is 53.3, can't I just do:
    2460+3x=53.3?
    But then I am not using a lot of the values provided and the answer in not in the options.
     
  2. jcsd
  3. Dec 27, 2015 #2

    Bystander

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    You have to make a "good faith" effort.
     
  4. Dec 27, 2015 #3
    Actually, I don't know what to do at all. I know that I have make a Hess's cycle so that I can form equations. But I can't figure out the Hess's cycle here.
     
  5. Dec 27, 2015 #4

    Bystander

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    What is Hess's cycle?
     
  6. Dec 27, 2015 #5
    The total enthalpy change is the same for all the routes the reaction can take to produce the product.
     
  7. Dec 27, 2015 #6

    Bystander

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    Correct. What route are you taking?
     
  8. Dec 27, 2015 #7
    Snapshot.jpg
    Let the C-C bond energy be x
    (3*-717) + (-436*3) + (410*6) + 3x = 53.3
    -2151-1308+2460+3x=53.3
    -999+3x=53.3
    3x=1052.3
    x=350.767
    approx. 351 kJ/mol

    But the answer should be 315kJ/mol.
     
  9. Dec 27, 2015 #8

    Bystander

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    Were you to use conventional notation, you might be more successful.
     
  10. Dec 28, 2015 #9
    What do you mean by conventional notation?
     
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: Enthalpy Change and Bond Energies
  1. Bond Enthalpies (Replies: 1)

  2. Bond Enthalpy (Replies: 2)

  3. Bond Enthalpy (Replies: 0)

Loading...