2012 practice final#2A

Volume:
Temperature:

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Lily Wei 1D
Posts: 10
Joined: Fri Sep 25, 2015 3:00 am

2012 practice final#2A

Postby Lily Wei 1D » Sat Mar 12, 2016 10:23 pm

For this problem, why is the change in entropy calculated using only
and not ? The problem states that "The He in the metal case is initially held at a pressure of 1.0 atm", so doesn't that mean that the pressure is going to change and we should take that into account?

Irena Roy 4H
Posts: 40
Joined: Fri Sep 25, 2015 3:00 am

Re: 2012 practice final#2A

Postby Irena Roy 4H » Sat Mar 12, 2016 10:48 pm

The question gives you no other information that could lead you to conclude that the pressure did actually change in the process of He leaking.

Alex Nguyen 3I
Posts: 100
Joined: Fri Sep 25, 2015 3:00 am

Re: 2012 practice final#2A

Postby Alex Nguyen 3I » Sat Mar 12, 2016 10:48 pm

Using the equation with volume change already accounts for the pressure change because of PV=nRT. Therefore you can use one or the other when finding the entropy. Only when there's a temperature change with a volume/pressure change do you need 2 equations with a combined entropy.

Suraj Palaparty 2F
Posts: 27
Joined: Fri Sep 25, 2015 3:00 am

Re: 2012 practice final#2A

Postby Suraj Palaparty 2F » Sat Mar 12, 2016 10:50 pm

The case is initially at 1.00 atm, taking into account the change in pressure later in the problem, while the safe is isolated.


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