Irreversible expansion


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Cristian Carrasco 1F
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Irreversible expansion

Postby Cristian Carrasco 1F » Mon Jan 29, 2018 2:47 pm

For irreversible expansion, why is w=P x delta V used instead of w= -nRt lnV2/V1?

Chem_Mod
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Re: Irreversible expansion

Postby Chem_Mod » Mon Jan 29, 2018 2:50 pm

For
P is constant

For
T is constant.

So they're used for different conditions.

Mike Vinci 2B
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Re: Irreversible expansion

Postby Mike Vinci 2B » Mon Jan 29, 2018 3:03 pm

For W=-nRTln v2/v1, we account for the infinitesimal and consistent change in expansion of the system. In class, we saw the curve Professor Lavelle drew whose shape was that of exponential decay. This comes from the use of the natural log. However, the important aspect to understand is that such a curve like that increases the space beneath the curve, and for that reason shows an increase in the change of enthalpy. For w=-p * delta V, we have only the change of space given by delta v, and with constant pressure, the space becomes fixed and therefore represents a fixed rectangle as Professor Lavelle also drew.

Amelia Georgius 1K
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Re: Irreversible expansion

Postby Amelia Georgius 1K » Wed Feb 07, 2018 5:28 pm

When pressure is constant, you can use the equation w= -PdeltaV, but when temperature is constant, you can use the other equation, w= -nRT lnV2/V1.

Shanmitha Arun 1L
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Re: Irreversible expansion

Postby Shanmitha Arun 1L » Wed Feb 07, 2018 5:38 pm

Simply put, it matters when P and T are constant. Based on that, certain equations are used.


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