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### DeltaU and DeltaH

Posted: **Thu Jan 25, 2018 8:38 pm**

by **104969854**

When does deltaU equal deltaH?

Does this happen in isochoric or isobaric conditions? What about at constant heat?

### Re: DeltaU and DeltaH

Posted: **Thu Jan 25, 2018 9:03 pm**

by **Angela 1K**

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.

### Re: DeltaU and DeltaH

Posted: **Thu Jan 25, 2018 9:47 pm**

by **Cristina Sarmiento 1E**

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.

### Re: DeltaU and DeltaH

Posted: **Wed Jan 31, 2018 6:55 pm**

by **Adrian Lim 1G**

What if there were a change in pressure?

### Re: DeltaU and DeltaH

Posted: **Wed Feb 14, 2018 12:20 am**

by **104969854**

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.