Delta U (Concept Clarification)


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Frenz Cabison 1B
Posts: 54
Joined: Fri Sep 29, 2017 7:07 am

Delta U (Concept Clarification)

Postby Frenz Cabison 1B » Sun Feb 04, 2018 5:29 pm

Why does gas expand if delta U is zero? I quite don't understand the concept behind this statement.

Masih Tazhibi 2I
Posts: 33
Joined: Fri Sep 29, 2017 7:06 am

Re: Delta U (Concept Clarification)

Postby Masih Tazhibi 2I » Sun Feb 04, 2018 5:46 pm

While the internal energy is zero, the gas is expanding against a vacuum which has no resistance.

Niyanta Joshi 1F
Posts: 30
Joined: Thu Jul 13, 2017 3:00 am

Re: Delta U (Concept Clarification)

Postby Niyanta Joshi 1F » Sun Feb 04, 2018 6:02 pm

There is no net change in internal energy as all the heat is used to to do expansion work against the surroundings.

Nora Sharp 1C
Posts: 53
Joined: Sat Jul 22, 2017 3:00 am

Re: Delta U (Concept Clarification)

Postby Nora Sharp 1C » Sun Feb 04, 2018 8:10 pm

viewtopic.php?f=130&t=26453

Here's a thread with some more information on the question you asked.

Helen Shi 1J
Posts: 78
Joined: Sat Jul 22, 2017 3:00 am

Re: Delta U (Concept Clarification)

Postby Helen Shi 1J » Mon Feb 05, 2018 11:58 am

In what cases is delta U=0? Why is delta U zero in an isothermal expansion?
Last edited by Helen Shi 1J on Mon Feb 05, 2018 12:10 pm, edited 1 time in total.

Wenjie Dong 2E
Posts: 53
Joined: Fri Jun 23, 2017 11:40 am

Re: Delta U (Concept Clarification)

Postby Wenjie Dong 2E » Mon Feb 05, 2018 12:04 pm

There is no change in internal energy in the system when delta U=0.

Sophia Kim 1C
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Re: Delta U (Concept Clarification)

Postby Sophia Kim 1C » Tue Feb 06, 2018 1:48 am

I think I read in the book that delta U is 0 because the molar internal energy of an ideal gas is U=3/2 RT and since internal energy and temperature are state dunctions DeltaU = 3/2 R DeltaT. So in an isothermal expansion where delta t = 0 , DeltaU would equal 0 as well.


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