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ΔH vs ΔU?

Posted: Wed Feb 13, 2019 9:00 am
by Anna O 2C
Can someone explain why heat transfer is ΔU at constant volume and interpreted as ΔH at constant pressure?

Re: ΔH vs ΔU?

Posted: Wed Feb 13, 2019 9:24 am
by Becky Belisle 1A
The formula for internal energy is: ΔU= q + w, so when volume is constant, w=0. Thus, when no work is done, ΔU = q. ΔH = q at constant pressure because if the pressure changed that would affect the enthalpy, but not the heat transfer.

Re: ΔH vs ΔU?

Posted: Wed Feb 13, 2019 4:46 pm
by haleyervin7
Can deltaU ever equal deltaH?

Re: ΔH vs ΔU?

Posted: Wed Feb 13, 2019 8:59 pm
by Cole Elsner 2J
Yes at constant pressure. If there is no net change in moles, there will be no work done. So there is the potential for deltaU=deltaH.

Re: ΔH vs ΔU?

Posted: Wed Feb 13, 2019 9:10 pm
by Soumya Ravichandran 4H
Yes, this can occur when there is no volume change (free expansion), but generally speaking, delta H will only equal delta U when there is no work done and pressure is held constant

Re: ΔH vs ΔU?

Posted: Wed Feb 13, 2019 11:53 pm
by Anjali_Kumar1F
If enthalpy is given do we automatically assume the reaction is at constant pressure.

Re: ΔH vs ΔU?

Posted: Tue Mar 05, 2019 6:41 pm
by Destiny Diaz 4D
When enthalpy is given I would not say it is safe to assume that pressure is constant, unless other wise stated.

Re: ΔH vs ΔU?

Posted: Tue Mar 12, 2019 1:20 pm
by Pritish Patil 1K
When volume is constant, work = 0 J. This means that deltaU = q.

Re: ΔH vs ΔU?

Posted: Thu Mar 14, 2019 2:35 pm
by CHEM 14B Lover
Can't there be expansion with constant pressure? Wouldn't that still be work done?