## 8.31

$\Delta U=q+w$

Christina_F_3F
Posts: 21
Joined: Fri Jul 22, 2016 3:00 am

### 8.31

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?

Taravat_Lakzian_1C
Posts: 18
Joined: Wed Sep 21, 2016 2:56 pm

### Re: 8.31

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
Posts: 10
Joined: Wed Nov 18, 2015 3:00 am

### Re: 8.31

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.