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Topic: Change in Enthalpy, delta H  (Read 4276 times)

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Offline a confused chiral girl

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Change in Enthalpy, delta H
« on: January 25, 2007, 11:11:36 PM »
Hi, I am having trouble with this problem --> 0.39 litre of an ideal monatomic gas (Cv = 3R/2) initially at 59 deg C and 2.3 atm pressure undergo an expansion against a constant external pressure of 1.13 atm, and do 2 kJ of work. The final pressure of the gas is 1.13. Calculate the change in enthalpy, Delta H.

I used deltaH = nCpdT, and found n, Vfinal, and T final. but I am not getting the correct answer which is supposed to be 4884 J .

Please show me the steps to this question, instead of dropping hints if possible. I need to know the steps for tomorrow's test. Thank u very much!!  :-*

Offline enahs

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Re: Change in Enthalpy, delta H
« Reply #1 on: January 26, 2007, 12:18:56 AM »
The equation you are using is correct. The first thing I would say to check is your units (because you did not show your actual work, or steps, I can only guess).

The reason I say so is, because you said the answer should be 4884J, enthalpy is usually given in kJ.

So the question is, what are you using for R and what are the units of R?
Do they cancel properly? Are you using the correct R that will work with liters and atm, or did you convert those units?

Offline Yggdrasil

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Re: Change in Enthalpy, delta H
« Reply #2 on: January 26, 2007, 12:27:50 PM »
What value are you using for Cp?

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