Most positive value of Delta S

Discussion in 'DAT Discussions' started by Awuah29, Apr 28, 2007.

  1. Awuah29

    Awuah29 Christian predent
    7+ Year Member

    Joined:
    Oct 13, 2003
    Messages:
    294
    Likes Received:
    0
    Ok, here another chem question!
    Why is the answer here #3 ? We going here from liquid to gas (exothermic)
    Delta H (-) Delta S (+) spontaneous at all temp
    Delta H (+) Delta S (-) Nonspontaneous at all temp ???

    How do I tackle this question here ?
    Thanks
     

    Attached Files:

  2. Note: SDN Members do not see this ad.

  3. llopop

    2+ Year Member

    Joined:
    Apr 7, 2007
    Messages:
    15
    Likes Received:
    0
    Okay first thing entropy is always increasing in the universe. As far as an individual reaction count the #of moles on each side. Whenever there is an increase in the #of moles there is a positive value for "Delta S". Another concept in this problem is that liquids have a lower state of order therefore going from a liquid to a gas would be a positive increase in "Delta S." The only answer that has both of these concepts is #3.

    As far as your other question a +H,-S will be spontaneous under low temps. -H,+S will be spontaneous under all temps. Hope that helped
     
  4. Lonely Sol

    Lonely Sol cowgoesmoo fan!
    10+ Year Member

    Joined:
    Dec 13, 2005
    Messages:
    684
    Likes Received:
    0
    Status:
    Pre-Dental
    I always thought +H, -S = non spontaneous at all temp and
    -H and -S, spontaneous only at low temp.

    Someone correct me if I am wrong
     
  5. llopop

    2+ Year Member

    Joined:
    Apr 7, 2007
    Messages:
    15
    Likes Received:
    0
    My bad i think I wrote that out wrong. If G=H-TS then -H,-S would occur under low temps, +H,-S would not occur under any temps and -H,+S would occur at all temps.
     
  6. jackbauer!

    jackbauer! Guest

    Joined:
    Jul 2, 2006
    Messages:
    1,703
    Likes Received:
    4
    Status:
    Dental Student
    not necessarily true. you must count the # of moles of gas on each side.

    d:thumbdown: = (# moles of gas as products) - (# moles of gas as reactants)

    if d:thumbdown: > 0, then d(S) is + (i.e. higher entropy, less order)
    if d:thumbdown: < 0, then d(S) is - (i.e. lower entropy, more order)
    if d:thumbdown: = 0, then must look at # of moles of solids & liquids

    hope this helps, jB!:)
     
  7. Awuah29

    Awuah29 Christian predent
    7+ Year Member

    Joined:
    Oct 13, 2003
    Messages:
    294
    Likes Received:
    0

    thanks Jack !:thumbup:
     
  8. jdmsamurai

    2+ Year Member

    Joined:
    Feb 11, 2007
    Messages:
    237
    Likes Received:
    1
    Status:
    Dental Student
    when i think of delta S think of total destruction and chaos...the world wants to be chaotic (less ordered)...if you have a book on the shelf...it wants to fall down into a pile......so if you tear apart a solid into a liquid...you increase the entropy...if you tear apart a liquid into a gas you increase the entropy because now this molecules are more chaotic......and if you tear two moles of gas into 3 moles of gas its more chaotic....imagine tearing apart a car into all its pieces....thats chaotic....aka increase of S
     
  9. BodybldgDoc

    BodybldgDoc Guest

    Joined:
    Jan 13, 2007
    Messages:
    712
    Likes Received:
    0
    Status:
    Pre-Health (Field Undecided)
    going from liquid ( more ordered state ) ---> to gas ( less ordered state) increases the entropy. If you look at the answer choices only #3 does this.
     

Share This Page