How to derive ΔH = ΔU + nRΔT


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Hannah Lee 2F
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Joined: Thu Jul 11, 2019 12:15 am

How to derive ΔH = ΔU + nRΔT

Postby Hannah Lee 2F » Fri Jan 31, 2020 9:02 pm

I'm confused about this equation: ΔH = ΔU + nRΔT, which is mentioned in the textbook.

I understand how to derive/use ΔH = ΔU + ΔnRT, but how could ΔU = ΔH - nRΔT be possible? I thought that in order to use any variation of ΔU = ΔH - PΔV, pressure had to be constant. However, in the book, it says you can use ΔU = ΔH - nRΔT to calculate the enthalpy of an ideal gas heated at a constant volume (not pressure). How would you derive that equation from the ideal gas law if volume is constant?

Jared Khoo 1G
Posts: 107
Joined: Wed Sep 18, 2019 12:16 am

Re: How to derive ΔH = ΔU + nRΔT

Postby Jared Khoo 1G » Fri Jan 31, 2020 10:23 pm

The standard formula for the first law of thermodynamics is . Here, W is equivalent to P , which by the ideal gas law is the same as nR , which is where this equation came from.


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