## Internal Energy

William Lan 2l
Posts: 73
Joined: Fri Sep 29, 2017 7:07 am

### Internal Energy

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

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

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

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

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

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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