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Topic: Calculating Cv,m and Cp,m  (Read 28727 times)

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Offline zerokun

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Calculating Cv,m and Cp,m
« on: May 30, 2008, 10:29:54 PM »
When 229 J of energy is supplied as heat to 3.0 mol of Ar (g) ,
the temperature of the sample increases by 2.55K .
Calculate the molar heat capacities at constant volume and constant pressure of the gas.
(Exercise :Atkins physical chemistry 8th p.p71 2.12 (a)
Answer : Cp,m = 30 J /K mol   and Cv,m =22 J /K mol)

To start this question,
I first think of the change in temperature is positive, so it is not adiabatic change.
W=229
Ar=3.0 mol
temp : + 2.55K
So i use the formula
qp= Cp (Tf-Ti )
              229 = Cp (2.55K)
Cp = 89.8 J / mol
therefore Cp,m = 89.8 J mol-1 /3mol  = 30 J / K mol
which is the correct answer.

But i cant come out with Cv,m
i try to use Cv,m = Cv/ n = Cv/3.0
and i cant continue from here

i wonder is there any relation between Cv and Cp??

Offline Yggdrasil

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Re: Calculating Cv,m and Cp,m
« Reply #1 on: May 30, 2008, 11:49:40 PM »

Offline zerokun

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Re: Calculating Cv and Cp
« Reply #2 on: May 31, 2008, 12:20:08 AM »
thank you

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