Turn on thread page Beta
    • Thread Starter
    Offline

    11
    ReputationRep:
    Hi. When you are calculating enthalpy changes and in one question you use mean bond enthalpies and in the other you use standard enthalpies of formation, it will often ask you why the values are different or why one value is more accurate. However, im not sure what to write for this as in two different mark schemes it gave different answers?
    It said:mean bond enthalpies are not exact

    and in another for 2 marks it said: bond enthalpies are mean/average values
    1 from a range of compounds
    What do i write in the exam?
    Offline

    10
    ReputationRep:
    (Original post by Bertybassett)
    Hi. When you are calculating enthalpy changes and in one question you use mean bond enthalpies and in the other you use standard enthalpies of formation, it will often ask you why the values are different or why one value is more accurate. However, im not sure what to write for this as in two different mark schemes it gave different answers?
    It said:mean bond enthalpies are not exact

    and in another for 2 marks it said: bond enthalpies are mean/average values
    1 from a range of compounds
    What do i write in the exam?
    you should write "bond enthalpies are mean values from a range of compounds" as the standard model answer.
    this will also correctly cover the answer "mean bond enthalpies are not exact" as mean bond enthalpy will not be the same as the true bond enthalpy for a particular bond in a particular compound.
    • Community Assistant
    • Study Helper
    Offline

    17
    ReputationRep:
    Community Assistant
    Study Helper
    (Original post by dip0)
    you should write "bond enthalpies are mean values from a range of compounds" as the standard model answer.
    this will also correctly cover the answer "mean bond enthalpies are not exact" as mean bond enthalpy will not be the same as the true bond enthalpy for a particular bond in a particular compound.
    You MUST also include "when measured over a range of GASEOUS compounds"
    Offline

    10
    ReputationRep:
    (Original post by charco)
    You MUST also include "when measured over a range of GASEOUS compounds"
    Yes thats correct I forget to mention that - thanks for bringing that point up.
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: March 5, 2018
The home of Results and Clearing

3,239

people online now

1,567,000

students helped last year

University open days

  1. London Metropolitan University
    Undergraduate Open Day Undergraduate
    Sat, 18 Aug '18
  2. Edge Hill University
    All Faculties Undergraduate
    Sat, 18 Aug '18
  3. Bournemouth University
    Clearing Open Day Undergraduate
    Sat, 18 Aug '18
Poll
A-level students - how do you feel about your results?

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

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