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Lindsay H 2B
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Postby Lindsay H 2B » Thu Feb 01, 2018 11:42 pm

This question asks for ∆S and ∆Stotal for 50.0 g H20 (l) at 20.0ºC mixing with 65.0 g H20 (l) at 50.0ºC at constant pressure in a thermally isolated vessel. Does ∆Stotal still refer to ∆S of the universe when the reaction happens in an isolated system?

Sammy Thatipelli 1B
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Re: 9.43

Postby Sammy Thatipelli 1B » Fri Feb 02, 2018 1:54 am

I believe deltaS is referring to the reaction happening, so it would be delta S of the reaction. I guess if the "universe" being referred to is the entire system in our reaction of hot and cold water, where you are adding hot and cold water's entropies, then you would be finding the deltaS Universe.

The definition of deltaS universe is the deltaS of the system+deltaS of the surroundings.

Angel Gomez 1K
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Joined: Fri Sep 29, 2017 7:04 am

Re: 9.43

Postby Angel Gomez 1K » Fri Feb 02, 2018 2:25 am

I also don't understand this question. Are we supposed to convert the grams of water to moles and use the molar heat capacity instead? I see that it says constant pressure, and that almost lead me to believe that I needed to use 5/2R for heat capacity. However, given that it's a liquid, doesn't that mean that pressure is insignificant?

Nha Dang 2I
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Re: 9.43

Postby Nha Dang 2I » Fri Feb 02, 2018 4:48 am

I believe you use 75.3 J/(molxK) which is the molar heat capacity.

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