Internal Energy

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William Lan 2l
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Joined: Fri Sep 29, 2017 7:07 am

Internal Energy

Postby William Lan 2l » Wed Jan 24, 2018 10:51 pm

If delta P = 0 (constant pressure), why is delta U = q + w? I thought that w = -PdeltaV. If P is 0, there would be no work then right?

Nancy Dinh 2J
Posts: 59
Joined: Fri Sep 29, 2017 7:07 am

Re: Internal Energy

Postby Nancy Dinh 2J » Wed Jan 24, 2018 10:52 pm

William Lan 2l wrote:If delta P = 0 (constant pressure), why is delta U = q + w? I thought that w = -PdeltaV. If P is 0, there would be no work then right?


In w = -P * delta V, you would plug in the constant pressure for P, not the change in P which would be delta P.

Chloe1K
Posts: 23
Joined: Fri Sep 29, 2017 7:05 am

Re: Internal Energy

Postby Chloe1K » Thu Jan 25, 2018 12:10 am

no change in pressure means ∆P=0, not P=0. the equation for work uses P not ∆P and it is unlikely P=0

Sophie 1I
Posts: 51
Joined: Fri Sep 29, 2017 7:04 am

Re: Internal Energy

Postby Sophie 1I » Thu Jan 25, 2018 9:43 pm

A change in pressure(delta P) does not necessarily mean that pressure is 0 it just means that the pressure is constant. The equation for work uses the actual pressure not the change in the pressure.

Cristina Sarmiento 1E
Posts: 52
Joined: Wed Nov 16, 2016 3:02 am

Re: Internal Energy

Postby Cristina Sarmiento 1E » Thu Jan 25, 2018 9:52 pm

If it was delta P instead of P in the equation, then pressure would equal 0 when it is constant.

JamesAntonios 1E
Posts: 70
Joined: Fri Sep 29, 2017 7:04 am

Re: Internal Energy

Postby JamesAntonios 1E » Thu Jan 25, 2018 10:42 pm

William Lan 2l wrote:If delta P = 0 (constant pressure), why is delta U = q + w? I thought that w = -PdeltaV. If P is 0, there would be no work then right?

That is a variation of the original equation. It all depends on what the environment/surrounding/situation is and whether the reaction is reversible or not.


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