Midterm 2007 Q3B- Explanation of (delta)S total






Moderators: Chem_Mod, Chem_Admin

Amy Luong 1L
Posts: 11
Joined: Fri Sep 26, 2014 2:02 pm

Midterm 2007 Q3B- Explanation of (delta)S total

Postby Amy Luong 1L » Sat Feb 07, 2015 9:08 pm

Would someone mind explaining why "delta S knot" is not a criterion for assessing the spontaneity of a reaction but the "delta S total rxn" shows that a reaction is spontaneous when it is greater than 0?

Satvir Saggi 1I
Posts: 22
Joined: Fri Sep 26, 2014 2:02 pm

Re: Midterm 2007 Q3B

Postby Satvir Saggi 1I » Sat Feb 07, 2015 9:58 pm

According to the second law of thermodynamics, "A spontaneous change is accompanied by an increase in the total entropy of the system and its surroundings." Therefore, we can only determine if a reaction is spontaneous based off the total change in entropy.

Chem_Mod
Posts: 17949
Joined: Thu Aug 04, 2011 1:53 pm
Has upvoted: 406 times

Re: Midterm 2007 Q3B- Explanation of (delta)S total

Postby Chem_Mod » Sun Feb 08, 2015 4:32 pm

Satvir is correct. To be spontaneous, TOTAL entropy must be positive. If we don't want to care about the surroundings, then we must use deltaG. If deltaG at constant T and P of the system is negative, then it is also spontaneous.

Showing the equivalence of spontaneity conditions:






Justin Le 2I
Posts: 142
Joined: Fri Sep 26, 2014 2:02 pm

Re: Midterm 2007 Q3B- Explanation of (delta)S total

Postby Justin Le 2I » Wed Feb 11, 2015 1:47 pm

since deltaG = deltaH - TdeltaS, we can't determine if a reaction is spontaneous if we are simply given deltaS. We need more information to see if deltaG is less than 0


Return to “Gibbs Free Energy Concepts and Calculations”

Who is online

Users browsing this forum: No registered users and 2 guests