AP Notes, Outlines, Study Guides, Vocabulary, Practice Exams and more!

Bond Enthalpy

bond enthalpy - enthalpy change for breaking of a bond

 

  • strength of covalent bond determined by amount of energy needed to break it
  • always positive value
  • DHrxn = (bond enthalpies of bonds broken) - (bond enthalpies of bonds formed)
  • derived for gaseous molecules, only averaged values

Find the DH for 2C2H6 + 7O2>> 4CO2 + 6H2O  

  • C2H6
  • CO2
  • H2O
  • Given bond enthalpies:
    • C-H 413 kJ/mol
    • C-C 348 kJ/mol
    • C=O 799 kJ/mol
    • H-O 463 kJ/mol
    • O2 495 kJ/mol
  • 2 C-C, 12 C-H, 7O2 bonds broken
  • 8 C=O, 12 H-O bonds created
  • [2(348) + 12(413) + 7(495)] - [8(799) + 12(463)] = -2831 kJ

Find the DH for N2H4 >> N2 + 2H2  

  • N2H4
  • N2
  • Given bond enthalpies:
    • N-H 391 kJ/mol
    • H-H 436 kJ/mol
    • N=N 941 kJ/mol
    • N-N 163
  • 1 N-N, 4 N-H bonds broken
  • 1 N=N, 2 H-H bonds created
  • [163 + 4(391)] - [941 + 2(436)] = -86 kJ
Subject: 
Chemistry
Subject X2: 
Chemistry

Need Help?

We hope your visit has been a productive one. If you're having any problems, or would like to give some feedback, we'd love to hear from you.

For general help, questions, and suggestions, try our dedicated support forums.

If you need to contact the Course-Notes.Org web experience team, please use our contact form.

Need Notes?

While we strive to provide the most comprehensive notes for as many high school textbooks as possible, there are certainly going to be some that we miss. Drop us a note and let us know which textbooks you need. Be sure to include which edition of the textbook you are using! If we see enough demand, we'll do whatever we can to get those notes up on the site for you!