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Ideal gas  monatomic or diatomic? 
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#1
Jan1512, 02:16 PM

P: 102

1. The problem statement, all variables and given/known data
5 moles of an idea gas at 300K at a pressure of 1.00 x 10^5 Pa is heated to 500K at constant pressure. The amount of heat transferred is 29.1kJ. Determine whether a gas is monatomic or diatomic through consideration of the values of the molar heat capacity at constant pressure C sub c,m and at C sub v,m 2. Relevant equations PV = nRT C = dQ/dT Cp = Cv + nR Cv = f/2 nR where f = 3 for monatomic gas and f = 5 for diatomic gas 3. The attempt at a solution No idea where to start... help please! 


#2
Jan1512, 03:09 PM

HW Helper
P: 6,187

In a constant pressure process you have Cp=dQ/dT. Can you calculate Cp from that? What would you get if you divide Cp by nR? 


#3
Jan1512, 03:16 PM

P: 102

Where dQ = 29.1x10^3 and dT = 200K then Cp = 145.5 J K^1
Is nR = 5 x 8.314 = 41.57 ???? but why would you do this? so Cp/nr = 3.5 ???? How does this relate? 


#4
Jan1512, 03:19 PM

HW Helper
P: 6,187

Ideal gas  monatomic or diatomic?
Yep. That is correct.
What would Cp/nR be for a monatomic gas? And for a diatomic gas? 


#5
Jan1512, 03:37 PM

P: 102

Cp = (f/2 +1) nR so then Cp/nR = (f/2 +1)
so for a monatomic gas... 3/2 + 1 = 2.5 for a diatomic gas... 5/2 +1 = 3.5 so the gas is diatomic? 


#7
Jan1512, 03:40 PM

P: 102

Thank you so much! I've been stuck on this for ages!



#8
Jan1512, 04:04 PM

P: 102

Just one question though what equation would be referenced for dividing Cp by nR?



#9
Jan1512, 04:11 PM

HW Helper
P: 6,187

Not sure what you mean...?
You've used 3 of your relevant equations and solved for "f". 


#10
Jan1512, 04:12 PM

P: 102

doh! Yeah, just noticed  thanks again!



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