Delta U = n*Cv,m*deltaT

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Samuel G Rivera - Discussion 4I
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Delta U = n*Cv,m*deltaT

Postby Samuel G Rivera - Discussion 4I » Wed Feb 12, 2020 11:01 am

Why does Delta U = n*Cv,m*deltaT apply for both constant pressure and constant volume?

Fatemah Yacoub 1F
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Re: Delta U = n*Cv,m*deltaT

Postby Fatemah Yacoub 1F » Wed Feb 12, 2020 9:27 pm

For constant pressure the Cv would actually be switched to CP.

Sean Cheah 1E
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Re: Delta U = n*Cv,m*deltaT

Postby Sean Cheah 1E » Thu Feb 13, 2020 11:16 am

Fatemah Yacoub 1F wrote:For constant pressure the Cv would actually be switched to CP.

Is this actually true? I thought that this equation for delta U only works with Cv. For example, in an isobaric process, q = nCp(delta T) and w = -P(delta V) = -nR(delta T). Thus delta U = q + w = n(Cp - R)(delta T). Since Cv = Cp - R, delta U = nCv(delta T).

Robin Cadd 1D
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Re: Delta U = n*Cv,m*deltaT

Postby Robin Cadd 1D » Thu Feb 13, 2020 2:40 pm

Sean Cheah 1E wrote:
Fatemah Yacoub 1F wrote:For constant pressure the Cv would actually be switched to CP.

Is this actually true? I thought that this equation for delta U only works with Cv. For example, in an isobaric process, q = nCp(delta T) and w = -P(delta V) = -nR(delta T). Thus delta U = q + w = n(Cp - R)(delta T). Since Cv = Cp - R, delta U = nCv(delta T).


I'm pretty sure it works for systems under both conditions.

Samuel G Rivera - Discussion 4I
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Re: Delta U = n*Cv,m*deltaT

Postby Samuel G Rivera - Discussion 4I » Fri Feb 14, 2020 1:50 pm

My TA sent us a list of equations and Cv wasn't changed to Cp when pressure is constant so Delta U = n*Cv,m*deltaT under constant pressure and constant volume. I was just wondering why since I thought you would need to use Cp under constant pressure.

Jarrett Peyrefitte 2K
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Re: Delta U = n*Cv,m*deltaT

Postby Jarrett Peyrefitte 2K » Fri Feb 14, 2020 4:14 pm

For constant volume, Cv is used.
For constant pressure, Cp is used.

Jaci Glassick 2G
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Re: Delta U = n*Cv,m*deltaT

Postby Jaci Glassick 2G » Fri Feb 14, 2020 5:33 pm

For constant pressure Cv is used and for constant volume Cp is used. My TA kind of mentioned that most of the time you are just going to end up using Cv but they both should work.

AniP_2D
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Re: Delta U = n*Cv,m*deltaT

Postby AniP_2D » Sun Feb 16, 2020 9:57 am

From information I gained from the book, discussion, and videos, I also believe that when talking about constant pressure, you use Cp, but when talking about constant volume, you use Cv.


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