Change in Entropy Equations


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Angela 1K
Posts: 80
Joined: Fri Sep 29, 2017 7:05 am

Change in Entropy Equations

Postby Angela 1K » Fri Mar 16, 2018 8:14 pm

I'm having difficulty differentiating between when to use the equation and .

If someone could please explain, that would be appreciated.

Thanks!

Curtis Wong 2D
Posts: 62
Joined: Sat Jul 22, 2017 3:00 am

Re: Change in Entropy Equations

Postby Curtis Wong 2D » Fri Mar 16, 2018 9:11 pm

Alright, so the first equation is typically the base for all the equations. It is useful for all scenarios because you can modify it. It's based on a constant temperature too.

The only instance where I found the second equation is when it talked about phase change. So, when there's a phase change, you use the second equation.

Angela 1K
Posts: 80
Joined: Fri Sep 29, 2017 7:05 am

Re: Change in Entropy Equations

Postby Angela 1K » Fri Mar 16, 2018 11:51 pm

Then how come, for example, in question 9.15, which asks to calculate the entropy change for (a) the freezing of 1.00 mol H2O(l) at 0.00 C and the vaporization of 50.0g of ethanol at 531.5K, the solutions manual uses the equation ? Why isn't it negative?


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