Delta S

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AMahadi
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Joined: Thu Jul 11, 2019 12:17 am

Delta S

Postby AMahadi » Thu Feb 13, 2020 3:04 pm

What is delta S total, if not delta S universe? Also, do you need to factor in temperature when determining if a reaction is spontaneous?

Ally Huang- 1F
Posts: 103
Joined: Thu Jul 25, 2019 12:16 am

Re: Delta S

Postby Ally Huang- 1F » Thu Feb 13, 2020 3:11 pm

Delta S total is the entropy change of the surroundings and the system. If delta S total is positive then the reaction is spontaneous. If only the delta s of the system is known then temperature and enthalpy are needed to determine if delta G is negative, and therefore spontaneous.

Pegah Nasseri 1K
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Joined: Wed Feb 27, 2019 12:15 am

Re: Delta S

Postby Pegah Nasseri 1K » Thu Feb 13, 2020 9:48 pm

The total change in entropy is simply the sum of the change in entropy of the system and the change in entropy of the surroundings. For example, in a reversible isothermal reaction, the change in entropy of the system is Delta S= nRln(V2/V1) and the change in entropy of the surrounding would be the negative value of this because the surrounding is reversing whatever change is done on the system. As a result, you know that the total change in entropy of a reversible isothermal reaction is 0.

Yes, temperature is factored when determining the spontaneity of a reaction by looking at the equation:
Delta G= Delta H - T(Delta S)
A negative Delta G value corresponds to a spontaneous reaction. Based off the values of your change in enthalpy and change in entropy you can determine whether the reaction would be spontaneous at higher or lower temperatures (whether your Delta G value will be negative).

Astrid Lunde 1I
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Joined: Sat Sep 07, 2019 12:16 am

Re: Delta S

Postby Astrid Lunde 1I » Fri Feb 14, 2020 9:59 am

delta S is the total between delta S of the surroundings and the system.

kendal mccarthy
Posts: 109
Joined: Wed Nov 14, 2018 12:22 am

Re: Delta S

Postby kendal mccarthy » Sun Feb 16, 2020 9:40 pm

DeltaS total= DeltaS system + DeltaS surroundings

And temperature does help determine if a reaction is spontaneous. Using the formula deltaG=deltaH - TdeltaH you can see if a reaction will be spontaneous or not depending on T.

Alan Cornejo 1a
Posts: 98
Joined: Fri Aug 30, 2019 12:15 am

Re: Delta S

Postby Alan Cornejo 1a » Sun Mar 15, 2020 7:28 am

The total enthropy is described using the equation total entropy is equal to the entropy of the system and surrounding added to eachother. For tempurature change including entropy we use the equation, deltaG = deltaH - T*deltaS, if our value of deltaG is negative then our reaction is spontaneous, if positive it is not.

Frank He 4G
Posts: 50
Joined: Tue Nov 12, 2019 12:19 am

Re: Delta S

Postby Frank He 4G » Sun Mar 15, 2020 7:34 am

The universe in the way we use it sometimes in this class is to refer to the thermodynamic universe or the parts that are relevant to our consideration of the thermodynamics of something we're studying. It is not the same as the thermodynamics of the entire universe. Thus the S of the universe can actually just mean the S total. I'd pay attention to context if it's ever needed to differentiate between which is being asked about.
Last edited by Frank He 4G on Sun Mar 15, 2020 7:35 am, edited 1 time in total.

Bryce Barbee
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Joined: Wed Sep 18, 2019 12:20 am

Re: Delta S

Postby Bryce Barbee » Sun Mar 15, 2020 7:35 am

Total includes surroundings and system.

Catherine Daye 1L
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Joined: Wed Sep 11, 2019 12:16 am

Re: Delta S

Postby Catherine Daye 1L » Sun Mar 15, 2020 7:37 am

Delta S total is the change in entropy in the system and surrounds. You should just add the change in entropy of the system and change in entropy of the surroundings.


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