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Topic: Pressure-volume work  (Read 3132 times)

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Offline Rimi

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Pressure-volume work
« on: February 16, 2012, 12:10:35 PM »
I just don't get this one at all..I've been trying it for a while now.



I have dW = -Pext*:delta:V  (not actually dW, but that fancy d like symbol. My professor calls it dW though).

If I integrate that I have...lets see if I can type this..



I can substitute Pgas with nRT/V so then my integral becomes

W= -nrT1/V dV

Which is -nRT1 ln(V2/V1)...but that's just going from A -> B right?

Is there even any work done from B -> C? I don't see any formulas that come with changing temperature with constant pressure. I'm not sure what to do with this.

And then here's the second part to the question.



I'm not really sure where to start. I can rewrite temperature as a function of p using the ideal gas law and then use that to find the differential. But just like before I don't see how temperature change factors into all of this.

Offline juanrga

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Re: Pressure-volume work
« Reply #1 on: February 17, 2012, 02:39:08 PM »
I just don't get this one at all..I've been trying it for a while now.



I have dW = -Pext*:delta:V  (not actually dW, but that fancy d like symbol. My professor calls it dW though).

If I integrate that I have...lets see if I can type this..



I can substitute Pgas with nRT/V so then my integral becomes

W= -nrT1/V dV

Which is -nRT1 ln(V2/V1)...but that's just going from A -> B right?

Is there even any work done from B -> C? I don't see any formulas that come with changing temperature with constant pressure. I'm not sure what to do with this.

And then here's the second part to the question.



I'm not really sure where to start. I can rewrite temperature as a function of p using the ideal gas law and then use that to find the differential. But just like before I don't see how temperature change factors into all of this.

There are two well-known thermodynamic coefficients that can be used to transform dV/V into (...)dp + (...)dT. One of those coefficients is the coefficient of isothermal expansion and is usually denoted by symbol ##\alpha##.
« Last Edit: April 03, 2012, 09:04:56 AM by Borek »
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