isothermal and deltaU=0


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Hannah Guo 3D
Posts: 56
Joined: Fri Sep 29, 2017 7:06 am

isothermal and deltaU=0

Postby Hannah Guo 3D » Tue Feb 13, 2018 8:27 pm

In homework 9.47(b) and also from Lavelle's slides, it says when there is an isothermal expansion, deltaU=0. Can someone explain how to lead to this conclusion? Thank you!

Andy Nguyen 1A
Posts: 56
Joined: Thu Jul 27, 2017 3:00 am

Re: isothermal and deltaU=0

Postby Andy Nguyen 1A » Tue Feb 13, 2018 8:33 pm

Using U=(3/2)*R*T, we know that this is the internal energy for an ideal gas. So that means the only thing changing U is temperature since (3/2) and R are constants. So since isothermal means the temperature doesn't change, deltaU=0.

Ramya Lakkaraju 1B
Posts: 67
Joined: Fri Sep 29, 2017 7:03 am

Re: isothermal and deltaU=0

Postby Ramya Lakkaraju 1B » Thu Feb 15, 2018 5:34 pm

Once we determine that delta U = 0, we can manipulate q and w and set q=-w.

Amanda Wu 2C
Posts: 31
Joined: Sat Jul 22, 2017 3:00 am

Re: isothermal and deltaU=0

Postby Amanda Wu 2C » Thu Feb 15, 2018 8:23 pm

For an ideal gas, delta U = (3/2)*R*delta T. If a system with an ideal gas is isothermal, then temperature remains constant, meaning delta T=0. Hence, if you calculate delta U with the aforementioned formula, delta U is also 0.

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