deltaG

[tRNA]

kaplan says
The minimum temprature at which the rxn is spontaneous is when deltaG=0

1)what is the minimum Temp. at which the rxn is nonspontaneous? is it also when deltaG=0?

2) what is the max Temp. at which the rxn is spontaneous? nonspontaneous?

any help, thanks

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[tRNA]

just wanted to clarify, only the statement above was made by kaplan, i got the questions from somewhere else,
please help me out guys, any ideas would help just to guide in the right direction, thanks

 

[jleefe]

A reaction is spontaneous when G is 0 or less. You can't know the min/max temp at which rxn is spontaneous without knowing the enthalpy (H) and entropy (S) of the reaction.

Following the G = H - TS formula, whenever H is smaller than TxS, G will be negative and thus the rxn will be spontaneous.

 

[TheWiredNerv]

A reaction is spontaneous when G is 0 or less. You can't know the min/max temp at which rxn is spontaneous without knowing the enthalpy (H) and entropy (S) of the reaction.

Following the G = H - TS formula, whenever H is smaller than TxS, G will be negative and thus the rxn will be positive.

What jleefe said. You have to know some information to apply the formula to the problem. The questions you asked can have different answers depending on what reaction and systems you are dealing with.

 

[113zami]

hmm... lets say the question is delta H= 120 and deltaS=60
if you were trying to find the mininum Temprature at which the rxn is spontaneous you just set deltaG=0 and solve for the T from the equation deltaG= deltaH-TdeltaS

but what about the minimum temp. at which the rxn is nonspontaneous??
can you find that out from the equation too? I think you can but I don't know how??



and for the max temp. at which the rxn is spont/nonspont, I don't think you can find that because under these conditions, when H and S are (+), above the minimum temp at which the rxn is spont. the rxn will always be spont regardless of how hi that temp is since G will always be (-) and above the minimum temp. at which the rxn is nonspont. the rxn will always be nonspont. regardless of how hi that temp is since delta G will always be (+)



but I have a feeling that i am missing something, anyone else please help us out because i think this is important to know for the dat

 

[rose786]

Ok, you need to know two things:

1) At equilibrium, G = 0
If it's negative, the reaction is spontaneous. If positive it's non spontaneous. You can look up why in your book.

2) Look in your review book or textbook and find a table relating G, H, S, and T. It will tell you the sign of G given the signs of two other variables. Memorize this table! It makes these type of questions much easier to solve.

 

[113zami]

believe me, I know that table and I have it memorized long time ago, but it seems that my problem is with applying stuff, and that table doesn't give you min/max values it just tells you at hi or low temp. but for this question you can actually find the value of the mininum Temprature at which the rxn is spontaneous from the deltaG equation which i have calculated to be = 2 ( whatever the units are),

so my question, is there a way to also find the actual value of the minimum temp. at which the rxn is nonspontaneous from the G equation or however?

thanks

 

[Smileen]

believe me, I know that table and I have it memorized long time ago, but it seems that my problem is with applying stuff, and that table doesn't give you min/max values it just tells you at hi or low temp. but for this question you can actually find the value of the mininum Temprature at which the rxn is spontaneous from the deltaG equation which i have calculated to be = 2 ( whatever the units are),

so my question, is there a way to also find the actual value of the minimum temp. at which the rxn is nonspontaneous from the G equation or however?

thanks

You can set the equation as : G=120-T60
For rxn to be spontanous; Delta G is negative or (0)
For rxn to be nonspontanous, Delta G is possitive
As you see from the equation, T=2k is the min temp for rxn to be spontanous. As T decreases (T<2K), delta G will become more positive, the reaction is nonspontanous. We can approximated the the min value of T for nonspontanous but we cannot know the actual value base on just the equation above. Hope this help somehow. Please correct me if I am wrong!

 

[113zami]

well, I don't know smileen, i guess, but I finally sent an email to my gchem prof. when he replies i'll let you know