Delta S


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Lucia H 2L
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Joined: Mon Nov 14, 2016 3:00 am
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Delta S

Postby Lucia H 2L » Sat Mar 17, 2018 12:32 pm

What exactly is the second law of thermodynamics in relation to delta S? I thought it was that delta s universe is always zero, but then a question on a practice final said that delta S total was positive so therefore a reaction was spontaneous.

What is delta S total, if not delta S universe? Also, don't you also need to factor in temperature when determining if a reaction is spontaneous, not just entropy?

Lily Sperling 1E
Posts: 49
Joined: Tue Oct 10, 2017 7:14 am

Re: Delta S

Postby Lily Sperling 1E » Sat Mar 17, 2018 12:37 pm

The second law can be written many ways, I know it as the entropy is always increasing in the universe. delta S only = 0 if the system is at equilibrium. deltaS universe=deltaSsys + deltaSsurr, meaning if deltaSuniv > 0, the process is spontaneous because both the entropy of the system, and the surroundings would have to be positive, which is what occurs naturally in the universe.

Justin Bui 2L
Posts: 51
Joined: Fri Sep 29, 2017 7:06 am

Re: Delta S

Postby Justin Bui 2L » Sat Mar 17, 2018 6:26 pm

I agree with Lily when she says that the main takeaway from the second law is that delta S total is always increasing and not 0 or decreasing. And yes, for spontaneity, you have to check delta H enthalpy and temperature as well to be sure about whether or not a process will be spontaneous.


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