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Topic: A question about reversibility  (Read 4171 times)

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Offline mortalapeman

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A question about reversibility
« on: September 19, 2010, 12:09:01 AM »
Ok the question I am working on is:

Calculate the final temperature of a sample of CO2 (16g) that is expanded reversibly and adiabatically from 0.5 L at 298.15 K to 2.0 L.

I know that adiabatic means the delta q = 0, however I'm really sure how that helps me with this problem. It seems more like the key word here is "reversibly". From my current understanding of this problem, that keyword means to solve this I need to hold pressure constant and just algebraically solve for T2. Is my understanding of this problem correct or am I missing something?

Thanks in advance,
ApeMan

Offline mortalapeman

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Re: A question about reversibility
« Reply #1 on: September 19, 2010, 11:54:30 AM »
I meant to say "I'm not really sure how that helps me", not "I'm really sure how that helps me". And btw where is the edit post button on this forum? I went straight to this page from my book marks and tried to edit it but i saw no link to do so.

Offline Jorriss

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Re: A question about reversibility
« Reply #2 on: September 19, 2010, 12:58:39 PM »
Next to quote there is a button that says modify, that's edit. Except, for me, it's only there about half the time...

Offline Borek

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Re: A question about reversibility
« Reply #3 on: September 19, 2010, 04:12:02 PM »
You can modify your posts only for a limited amount of time.
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Offline mortalapeman

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Re: A question about reversibility
« Reply #4 on: September 19, 2010, 09:39:13 PM »
Ah and i just realized that i forgot to say what i was asking to find. I'm looking for w,q, delta U and delta H. So since nobody seems to have an idea what i'm talking about, maybe someone could solve for one of those variable and it would answer my question xD

Offline MrTeo

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Re: A question about reversibility
« Reply #5 on: September 20, 2010, 03:02:02 PM »
If a transformation is reversible you can evaluate the work done using this expression:

$$ W=\int_{V_i}^{V_f}pdV /$$

And no, the pressure is not constant... here is the formula for a reversible adiabatic:



where



Now you have all the infos you need to solve your problem... use for CO2 the cV and cp values of a biatomic gas (if I remember well...).
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