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Emma Ward 2C
Posts: 32
Joined: Fri Sep 29, 2017 7:05 am


Postby Emma Ward 2C » Sun Feb 11, 2018 1:42 pm

the question states that "during the test of an internal combustion engine, 3.00 L of nitrogen gas at 18.5 degrees C was compressed suddenly (and irreversibly) to .500 L by driving in a piston. In the process, the temp of the gas increased to 28.1 degrees C. Assume ideal behavior and 1 mole of Nitrogen gas. What is the entropy of the gas?"

I understand that you can split this problem into two separate entropy problems, one for the change in volume and one with a change in temp because it's a state function. Lavelle identified that this problem is wrong in the solution manual but on his correction on his website, when solving delta S= nCvlnT2/T1, it says that Cv= 5/2R, but on the equation sheet it says Cv= 3/2R for an ideal gas. If someone could just help me see whether I am making a mistake or misunderstanding something or if that was just a typo? thanks!

Sarah Rutzick 1L
Posts: 50
Joined: Tue Oct 10, 2017 7:13 am

Re: 9.13

Postby Sarah Rutzick 1L » Sun Feb 11, 2018 2:44 pm

I believe it is a typo and I would trust the formula sheet.

Kyle Sheu 1C
Posts: 87
Joined: Fri Jun 23, 2017 11:39 am

Re: 9.13

Postby Kyle Sheu 1C » Sun Feb 11, 2018 2:48 pm

N2 is a diatomic gas and has more degrees of freedom due to greater rotational energy. Cv is 5/2R

Tia Tomescu 2D
Posts: 42
Joined: Fri Sep 29, 2017 7:06 am

Re: 9.13

Postby Tia Tomescu 2D » Sun Feb 11, 2018 2:59 pm

Page 281 of the textbook gives a good summary of the Cp and Cv for atoms, linear molecules, and nonlinear molecules.

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