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Postby Christina_F_3F » Sun Jan 22, 2017 9:49 pm

Q 8.31: "Calculate the heat released by 5.025 g of Kr (g) at 0.400 atm as it cools from 97.6 degrees C to 25 degrees C at a constant pressure"

The solution for this question says "The molar heat capacity of a monatomic ideal gas at constant is C=5/2R."

Where was this number derived from? Is it simply something we should know, or is there a way to prove this?

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Re: 8.31

Postby Taravat_Lakzian_1C » Sun Jan 22, 2017 11:38 pm

I believe it is derived from the equation:
Cp,m=Cv,m + R
Cp,m=3/2R + R
Cp,m = 5/2 R

Section 8.10 in the book provides more information about the molar heat capacity at a constant volume/pressure for monatomic gases. I don't think we have to memorize this since it is also found on the back of our periodic table of elements. Hope this helps!

Kristen Hazama 1I
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Re: 8.31

Postby Kristen Hazama 1I » Sun Jan 22, 2017 11:46 pm

I believe it was from the Constants and Equations sheet on the back of our periodic tables. It says: Monatomic ideal gas: U=3/2nRT; Cv = 3/2R; Cp = 5/2R. Since the problem says to assume krypton behaves as an ideal gas, I used these equations.

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