Midterm Question

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Kimberly 1H
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Midterm Question

Postby Kimberly 1H » Sun Feb 17, 2019 1:07 pm

On the midterm, the last questions asked for the change in entropy of nitrogen gas that went through a change in temperature and volume. Did it matter if we used the C value of an ideal gas or of nitrogen itself?

Lauryn Shinno 2H
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Re: Midterm Question

Postby Lauryn Shinno 2H » Sun Feb 17, 2019 1:24 pm

I think if you used the Cp value 5/2*R you would get a value around 20.785. The value they gave us during the exam was 20.81, so I think if you used either you would get around the same answer.

Lasya Gudipudi 1A
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Re: Midterm Question

Postby Lasya Gudipudi 1A » Sun Feb 17, 2019 3:39 pm

Yeah, I just used the equation for constant pressure of an ideal gas to solve for the heat capacity of nitrogen gas.

Gracie Ge 2E
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Re: Midterm Question

Postby Gracie Ge 2E » Wed Feb 20, 2019 10:30 pm

i think you're not supposed to use Cpm here because for the second part of the solution since it's at constant V. the constant given in the solutions also stated that 20.81 was the Cv,m of nitrogen gas, not Cp,m.
(i used 3/2*R to calculate the Cv,m and was given points as well.

Matthew Tran 1H
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Re: Midterm Question

Postby Matthew Tran 1H » Wed Feb 20, 2019 11:22 pm

It was also important to note that nitrogen is a diatomic gas. The values on the equation sheet are those for monatomic ideal gases, so you would have to add R to each for diatomic ideal gases (therefore Cv,m for N2 is about (5/2)R). You had to use Cv,m because you broke it up into two steps: increase in volume then increase in temperature (at the final volume).

abbydouglas1K
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Re: Midterm Question

Postby abbydouglas1K » Fri Feb 22, 2019 9:07 am

if you used the constant given for constant pressure 5/2R you should have gotten a value close the actual C that as even about an hour into the test.

Jocelyne Milke 1G
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Re: Midterm Question

Postby Jocelyne Milke 1G » Fri Feb 22, 2019 5:44 pm

I think they accepted either one

Carissa Young 1K
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Re: Midterm Question

Postby Carissa Young 1K » Fri Feb 22, 2019 8:49 pm

I used C=5/2R and I got full credit, maybe it doesn't matter that much?

Lopez_Melissa-Dis4E
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Re: Midterm Question

Postby Lopez_Melissa-Dis4E » Fri Feb 22, 2019 9:20 pm

I believe either one gave approximately the same answer.


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