DeltaU and DeltaH


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104969854
Posts: 36
Joined: Fri Sep 29, 2017 7:05 am

DeltaU and DeltaH

Postby 104969854 » Thu Jan 25, 2018 8:38 pm

When does deltaU equal deltaH?
Does this happen in isochoric or isobaric conditions? What about at constant heat?

Angela 1K
Posts: 80
Joined: Fri Sep 29, 2017 7:05 am

Re: DeltaU and DeltaH

Postby Angela 1K » Thu Jan 25, 2018 9:03 pm

occurs when the volume is constant. If you want to derive this, the equation for is . Thus, when there is no change in volume, and so . Thus, . Not 100% sure, but I hope this helped.

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

Re: DeltaU and DeltaH

Postby Cristina Sarmiento 1E » Thu Jan 25, 2018 9:47 pm

Delta U = Delta H when there is constant pressure and constant volume. Remember that Delta U = q +w. Delta H = q when there is constant pressure. w= -P Delta V. So when volume is constant, Delta V = 0. Therefore when there is constant pressure and volume, you can substitute q & w and get delta U = delta H.

Adrian Lim 1G
Posts: 88
Joined: Fri Sep 29, 2017 7:03 am

Re: DeltaU and DeltaH

Postby Adrian Lim 1G » Wed Jan 31, 2018 6:55 pm

What if there were a change in pressure?

104969854
Posts: 36
Joined: Fri Sep 29, 2017 7:05 am

Re: DeltaU and DeltaH

Postby 104969854 » Wed Feb 14, 2018 12:20 am

Angela 1K wrote: occurs when the volume is constant. If you want to derive this, the equation for is . Thus, when there is no change in volume, and so . Thus, . Not 100% sure, but I hope this helped.


Hi, I'm looking back at this and I'm just confused because your explanation totally makes sense with the equation you gave, and because I know that with constant volume work equals 0 so q=delta U. with your explanation, would this make delta H=delta U=q under constant volume, and people are saying that q is only equal to delta H under constant pressure....I'm just lost with the inconsistency and was wondering if you could elaborate a bit.


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