Calculating final pressure

  • Thread starter fiziks09
  • Start date
  • #1
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Homework Statement




As a 1.00 mol sample of a monoatomic gas expands adiabatically the work done on it is
-2.50x10^3J. The initial temperature and pressure of the gas are 500k and 3.60atm. Calculate
a. The final temperature and b. The final pressure.


Homework Equations



First law of thermodynamics
Eint = Q + W

The Attempt at a Solution


I was able to solve the first part of the question. Since it was an adiabatic process Q = 0 and then used Eint = nCv(Tb - Ta) to get the final temperature which is 300k.

But i can't seem to get the final pressure. I have no idea on how to begin. Please any help will be very much appreciated.
 

Answers and Replies

  • #2
263
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Use the state equation for an adiabatic process i.e. p*T^(k/(1-k))=constant. Where k is the quotient of the heat capacities.
 
  • #3
28
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quotient of heat capacities?? please i don't understand that part!!!!
 
  • #4
263
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Its just that k=C_p/C_v. The quotient of the heat capacities at constant pressure and constant volume.
 
  • #5
28
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okay..i get that part.. is the constant R??
 
  • #6
263
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No... that equation means that this quantity p*T^(k/(1-k)) is constant throughout the process. Which means that its the same in the beginning and at the end. U know the pressure and temperature at the beginning you know tht temp at the end...
 
  • #7
28
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ok.. but i'm getting a wrong answer which is 5.9atm but it should be 1atm...
 
  • #8
263
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Are you making your calculations correctly? whats the value you got for k for the gas?
 
  • #9
28
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i got 1.5
i used C_v to be 3/2R since the gas is monoatomic and C_p to be 5/2R
 
  • #10
263
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shouldnt it be 1.667? And then whats the next step? show the whole calculation otherwise i cant see wtz wrong...
 

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