Results are out! Find what you need...fast. Get quick advice or join the chat
Hey! Sign in to get help with your study questionsNew here? Join for free to post

Bond Enthalpy Calculations

Announcements Posted on
Don't forget to check out our results day hub. See you on the day for celebration and support, good luck! 22-06-2015
Will you get the grades you need for uni? Get prepared today and de-stress, sign up to email alerts for course places! 02-06-2015
  1. Offline

    ReputationRep:
    Ok Hess cycles next lesson - Want to consolidate this first though, so the answer will be either exothermic or endothermic. This process should show what exactly... it doesnt show how much energy the reactants have, just the energy required to break their bonds.

    C2H6+3.5O2 = 2CO2+3H2O

    Excuse the equals, ok so this reaction is exothermic, how much so?
    Method,

    Energy in (to break bonds)
    6 * C-H (6*413=2478)
    3 * O=O (3*498) (Theres a 0.5 here, how is that bonded and calculated?)

    Energy out (create bonds)
    4 * C=O (4*805=3220)
    6 * O-H (6*464=2784)

    Questions
    I guess its then Energy out - Energy in for your answer?
    I just want to make sure i know all the main points about this, does it show how much energy a molecule has, or just how much is released/sucked in when it reacts?
    Does this method of calculating enthalpy change have name?
    Answer is always negative for exothermic reaction?

    Any other related theory welcome, AS level. Thanks
  2. Offline

    ReputationRep:
    energy required (endo, +)
    1 x C-C
    6 x C-H
    3.5 x O=O

    energy released (exo, -)
    4 x C=O
    6 x O-H

    sum

    (1 x C-C) + (6 x C-H) - (4 x C=O) - (6 x O-H)

    as straightforward as that.
  3. Offline

    ReputationRep:
    Can someone answer the questions :confused:
  4. Offline

    ReputationRep:
    (Original post by LearningMath)

    Questions
    I guess its then Energy out - Energy in for your answer?
    1. I just want to make sure i know all the main points about this, does it show how much energy a molecule has, or just how much is released/sucked in when it reacts?
    2. Does this method of calculating enthalpy change have name?
    Answer is always negative for exothermic reaction?

    Any other related theory welcome, AS level. Thanks
    1. This calculation shows the energy change when 1 mole of ethane is burned in excess air or oxygen.
    A combustion is always exothermic therefore it's always a negative value.

    2. No specific name. Reaction enthalpy by the bond energy method.

    3. By definition the enthalpy change of an exothermic process is negative.
  5. Offline

    ReputationRep:
    Thank you... Had an idea it was more complicated.... Meh oh well, cheers

Reply

Submit reply

Register

Thanks for posting! You just need to create an account in order to submit the post
  1. this can't be left blank
    that username has been taken, please choose another Forgotten your password?
  2. this can't be left blank
    this email is already registered. Forgotten your password?
  3. this can't be left blank

    6 characters or longer with both numbers and letters is safer

  4. this can't be left empty
    your full birthday is required
  1. By joining you agree to our Ts and Cs, privacy policy and site rules

  2. Slide to join now Processing…

Updated: September 24, 2008
New on TSR

How high will tuition fees go?

Students share their thoughts on possible increases

Study resources
Article updates
x

Think you'll be in clearing or adjustment?

Hear direct from unis that want to talk to you

Get email alerts for university course places that match your subjects and grades. Just let us know what you're studying.

Quick reply
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.