Hey there! Sign in to join this conversationNew here? Join for free
x Turn on thread page Beta
    • Thread Starter
    Offline

    10
    ReputationRep:
    Name:  Screenshot_2016-02-17-20-32-06.png
Views: 31
Size:  136.6 KB why is there another - sign on the -248?
    Offline

    11
    ReputationRep:
    (Original post by gomc)
    Name:  Screenshot_2016-02-17-20-32-06.png
Views: 31
Size:  136.6 KB why is there another - sign on the -248?
    ΔHr = Σ[ΔHf(products)] - Σ[ΔHf(reactants)] = ΔHf(CH3CHOHCH3) - [ΔHf(CH3COCH3) + ΔHf(H2)]ΔHf(H2) = 0 by definition

    Therefore ΔHr = ΔHf(CH3CHOHCH3) - ΔHf(CH3COCH3)
    ΔHf(CH3CHOHCH3) = -318 kJ mol-1
    ΔHf(CH3COCH3) = -248 kJ mol-1

    ΔHr = -318 -(-248)
    = -318 + 248
    = -70 kJ mol-1

    There's two minus signs because you have to subtract the enthalpy of formation of CH3COCH3 which is negative itself.


    Hope this helps you out.
    • Thread Starter
    Offline

    10
    ReputationRep:
    (Original post by Jpw1097)
    ΔHr = Σ[ΔHf(products)] - Σ[ΔHf(reactants)] = ΔHf(CH3CHOHCH3) - [ΔHf(CH3COCH3) + ΔHf(H2)]ΔHf(H2) = 0 by definition

    Therefore ΔHr = ΔHf(CH3CHOHCH3) - ΔHf(CH3COCH3)
    ΔHf(CH3CHOHCH3) = -318 kJ mol-1
    ΔHf(CH3COCH3) = -248 kJ mol-1

    ΔHr = -318 -(-248)
    = -318 + 248
    = -70 kJ mol-1

    There's two minus signs because you have to subtract the enthalpy of formation of CH3COCH3 which is negative itself.


    Hope this helps you out.
    Thank you!
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: February 17, 2016
Poll
Do you agree with the proposed ban on plastic straws and cotton buds?

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.