Chemical Forums
Chemistry Forums for Students => Physical Chemistry Forum => Topic started by: zerokun on May 30, 2008, 10:29:54 PM
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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??
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http://en.wikipedia.org/wiki/Heat_capacity#Relation_between_specific_heats
Note that Ar can be treated as an ideal gas.
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thank you