Most positive value of Delta S

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

1. Awuah29 Christian predent 7+ Year Member

Joined:
Oct 13, 2003
Messages:
294
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:

• clip_image002.zip
File size:
13 KB
Views:
73
Stop hovering to collapse... Click to collapse... Hover to expand... Click to expand...
2. llopop 2+ Year Member

Joined:
Apr 7, 2007
Messages:
15
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

3. Lonely Sol cowgoesmoo fan! 10+ Year Member

Joined:
Dec 13, 2005
Messages:
684
1
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

4. llopop 2+ Year Member

Joined:
Apr 7, 2007
Messages:
15
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.

5. jackbauer! Guest

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

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

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

hope this helps, jB!

Stop hovering to collapse... Click to collapse... Hover to expand... Click to expand...
6. OP

Awuah29 Christian predent 7+ Year Member

Joined:
Oct 13, 2003
Messages:
294
0

thanks Jack !

Stop hovering to collapse... Click to collapse... Hover to expand... Click to expand...
7. jdmsamurai 2+ Year Member

Joined:
Feb 11, 2007
Messages:
237
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

8. BodybldgDoc Guest

Joined:
Jan 13, 2007
Messages:
712
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.

We’ve been on the Internet for over 20 years doing just one thing: providing career information for free or at cost. We do this because we believe that the health education process is too expensive and too competitive.

We believe that all students deserve the same access to high quality information. We believe that providing high quality career advice and information ensures that everyone, regardless of income or privilege, has a chance to achieve their dream of being a doctor.