#4 on practice midterm


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Lucia H 2L
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#4 on practice midterm

Postby Lucia H 2L » Wed Feb 14, 2018 12:37 am

You have a system consisting of 0.60 moles of an ideal gas contained in a 50.0L container at 1.0 atm.
You just love chemistry to a fault, so you perform a series of steps to the system. First, you perform an
isobaric compression of the container to 20.0L. Then, you pressurize the system to 8.0 atm using an
isochoric method. Finally, you perform a reversible, isothermal expansion (now at 1,234 K) on your
system back to a 50.0L volume at 1.0 atm. Now, to apply your knowledge, you must calculate ∆U, q, w,
and ∆S of the system specifically over the entire process. Much fun!

Can someone explain what they did for step 3?
I have:
step 1: work= -PdeltaV = 3039.5 J
step 2: work = 0
step 3: work = -nRTln(V2/V1)? How do you get the pressure back down from 8 atm? or is it assumed that it will automatically return to 1atm in the expansion?

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Re: #4 on practice midterm

Postby Chem_Mod » Wed Feb 14, 2018 9:49 am

The system should have returned to the same initial state, so the formula for reversible isothermal expansion would be used. That formula accounts for pressure changes.

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