Enthalpy Equation


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Andrew Nguyen 2I
Posts: 68
Joined: Fri Sep 29, 2017 7:07 am

Enthalpy Equation

Postby Andrew Nguyen 2I » Wed Jan 17, 2018 4:46 pm

So, I know how the enthalpy equation is derived to equal the heat added to a system. Though - why is it possible to say enthalpy = U+PV

I'm a little confused about what enthalpy is I guess and why its equation makes sense.

Also in H = delta U + PdeltaV
what is PdeltaV symbolizing, since delta U = q + PdeltaV ?

Jasmine Botello 2F
Posts: 67
Joined: Fri Sep 29, 2017 7:04 am

Re: Enthalpy Equation

Postby Jasmine Botello 2F » Wed Jan 17, 2018 6:52 pm

PdeltaV represents work. so the equation would be deltaU= q+w and w=-PdeltaV.

Ya Gao
Posts: 52
Joined: Fri Sep 29, 2017 7:04 am
Been upvoted: 1 time

Re: Enthalpy Equation

Postby Ya Gao » Wed Jan 17, 2018 7:24 pm

Hey, P∆V represents work done to the system. Since w=FxD and F=PxA D (distance) and A (area), we can get the equation w=P ∆V.
Hope it helps.

Yutian Zhao -1J
Posts: 30
Joined: Fri Sep 29, 2017 7:05 am

Re: Enthalpy Equation

Postby Yutian Zhao -1J » Sat Jan 20, 2018 1:44 pm

according to U=q+w, under constant P(delta H=qp),when there is an expansion, work is done by the system, therefore w=-P*delta V (P is constant so only V changes, and since work is done by the system, there is a negative sign in the front); and:
=delta H+w
=delta H+(-P*delta V)
=delta H- P*delta V
deltaH =U+P*delta V (put -P*delta V in the last equation to the left side of the equation)

Hope it helps!

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