j4yman
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Spontaneous reaction
I'm having trouble with this question...
For the process S8 (rhombic) --> S8 (monoclinic) at 110°C.
ΔH = 3.21 kJ mol-1 and ΔS = 8.70 J K-1 mol-1 (at 110°C).
Which of the following is correct?
a) This reaction is spontaneous at 110°C and S8 (monoclinic) is more stable than S8 (rhombic).
b) This reaction is spontaneous at 110°C and S8 (rhombic) is more stable than S8 (monoclinic).
c) This reaction is nonspontaneous at 110°C and S8 (rhombic) is more stable than S8 (monoclinic).
d) This reaction is nonspontaneous at 110°C and S8 (monoclinic) is more stable than S8 (rhombic)
e) Need more data.
So far i've used the formula to find ΔG to be -122.1
This means it is a spontaneous process, so it can't be c) or d). I'm pretty sure it isn't e)
How do i know which is more stable ?...a or b?
Thx.
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Darkblade48
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I'm getting an answer of -132.105 J for ΔG, using T = 384.15 K (If you use 384 K, you get -130.8 J for ΔG).
Anyhoo, since your ΔG is negative, it definitely means the reaction is spontaneous (at least, assuming that this is a homework problem, and since
you're given no other information...)
As for the whether or not S8 (monoclinic) is more stable than S8 (rhombic), I was under the impression that you could figure that out simply looking
at the ΔG value. Since it's negative, it means the reaction will prefer to proceed as written, and from thre, you can figure out which one is
more stable.
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Microtek
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Negative delta G does not necessarily mean that a reaction is spontaneous; if the activation energy is large enough, the reaction may never happen.
Think of diamond in air ( C + O2 --> CO2 ) or any stable explosive. If I got that question I would answer "need more data" ( and the professor
would probably count it as an error ).
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chemoleo
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I can't remember details, but doesn't the arrhenius equation answer at least part of your question? I hope I am not talking out of my backside...
Never Stop to Begin, and Never Begin to Stop...
Tolerance is good. But not with the intolerant! (Wilhelm Busch)
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guy
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If it is endothermic, then wouldn't it be less stable?
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neutrino
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Strictly speaking, a negative delta G does make a reaction spontaneous. It may not happen at any significant rate, but it will still technically be
spontaneous. In other words, the reaction will ultimately proceed to the right.
About stability, do you look at delta H or delta G? I thought it was H, but I'm not so sure.
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Darkblade48
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| Quote: | Originally posted by neutrino
About stability, do you look at delta H or delta G? I thought it was H, but I'm not so sure. |
Wouldn't you look at delta G? Doesn't stability depend on both the heat of reaction as well as entropy?
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guy
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Actually yeah I think free energy determines stability.
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j4yman
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BTW, the answer was
a) This reaction is spontaneous at 110°C and S8 (monoclinic) is more stable than S8 (rhombic).
Thanks for the help, I got it right.!
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chunkydrive
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Hey, do you go to UQ? Check your U2U
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