## test problem 4A.5 continued

isochoric/isometric: $\Delta V = 0$
isothermal: $\Delta T = 0$
isobaric: $\Delta P = 0$

JosephineF
Posts: 49
Joined: Wed Sep 18, 2019 12:17 am

### test problem 4A.5 continued

Why does this problem use $w=-P\Delta V$ for an irreversible expansion but w=-nRTln(V2/V1) for a reversible expansion?

LBacker_2E
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Joined: Wed Sep 18, 2019 12:21 am
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### Re: test problem 4A.5 continued

You always use w=Pex x (delta)V for an irreversible expansion because the change in volume is measurable. For a reversible process you use the other equation because the change in volume is infinitestimally small. For the reversible expansion, pressure falls as the volume increases which is reflected by the nRT part of the equation from PV=nRT.

Grace Jansen 2A
Posts: 28
Joined: Sat Jul 20, 2019 12:16 am

### Re: test problem 4A.5 continued

If you look back at the notes, you can see Dr. Lavelle derive the equation for the reversible expansion. Additionally, it is also in the book.