Example 8.6


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

Example 8.6

Postby Angela 1K » Thu Jan 11, 2018 9:00 pm

The question asks:
Calculate the final temperature and the change in internal energy wen 500. J of energy is transferred as heat to 0.900 mol O2(g) at 298 K and 1.00 atm at (a) constant volume; (b) constant pressure. Treat the gas as ideal.

I understand how the textbook determine CV,m and CP,m, but I don't understand where they get the equations for parts (a) and (b) from. This is the work that the textbook show:

(a) From ,


Find the final temperature.
T = 298 + 26.7 K = 325 K
From at constant volume,


(b) From

Find the final temperature.
T = 298 + 19.1 K = 317 K

Heat at constant volume: Transfer enough energy to raise the temperature to its final value (317 K), and use


Expand at constant temperature: Allow the sample to expand isothermally to its final volume.
Because U is independent of volume for an ideal gas,

Now add the two changes in internal energy.


Sorry for the long problem but if someone could please explain it to me (step-by-step) regarding why they used each equation and how they got to each step, that would be greatly appreciated. Thank you so much!

Lena Nguyen 2H
Posts: 51
Joined: Fri Sep 29, 2017 7:06 am
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Re: Example 8.6

Postby Lena Nguyen 2H » Thu Jan 11, 2018 9:22 pm

For part (a), the first formula is the equation from the textbook but modified so that is on its own side. From , the final temperature is calculated.

at constant volume because no expansion work is done (assuming no nonexpansion work is done either), so w = 0.

Sorry, I'm not sure I completely understand the ideal gas has when expanding isothermally in part (b), but I hope this helped with part (a).


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