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Thermodynamics - Please help me to calculate the final gas pressure.

  1. Feb 26, 2012 #1
    1. The problem statement, all variables and given/known data
    A fixed mass of gas at a constant pressure of 1 x 105 N/m2 (pascal) expands to twice its volume at constant temperature of 27°C. The volume is then kept constant, and the gas is heated to 87°C. Calculate the final gas pressure.

    2. Relevant equations
    I think this is the equation PV/nT=R that I need for this question.

    3. The attempt at a solution
    I am clueless to be honest. I am only given pressure and temperature to work this out. Can anyone please help me?
     
  2. jcsd
  3. Feb 26, 2012 #2

    Astronuc

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    Staff: Mentor

    Well the system is closed to the number of atoms (or moles) is fixed. Given three variables P, V, T, if one is fixed, then there is a linear relationship between the other two. For example if T is fixed (constant), then by the ideal gas law, PV = some constant. So if V doubles, what happen to P?
     
  4. Feb 26, 2012 #3
    Then, volume is constant, apply pressure law.
    [itex]\frac{p_{1}}{T_{1}}[/itex] = [itex]\frac{p_{2}}{T_{2}}[/itex]
    *Remember to change the temperature from oC to K
     
    Last edited: Feb 26, 2012
  5. Feb 26, 2012 #4
    Thank you guys for your help. I worked it out and I have got the answer 12 x 104..is this correct?
     
  6. Feb 26, 2012 #5

    Astronuc

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    Staff: Mentor

    It would help if one were to show the steps (equations) and provide units with the numbers.
     
  7. Feb 26, 2012 #6
    I worked it out using the formula mentioned above on this thread. So P1 = 1x105 N/m2, T1 = 27°C + 273 = 300K, P2 = ? & T2 = 87°C + 273 = 360K.

    1 x 105N/m2 / 300 = P2 / 360
    1x105 x 360 = P2 x 300
    1x105 x 360 / 300 = P2
    P2 = 12 x 104 N/m2
     
  8. Feb 26, 2012 #7
    p1 is not correct because "a constant pressure of 1 x 105 N/m2 (pascal) expands to twice its volume at constant temperature of 27°C"
     
  9. Feb 27, 2012 #8
    th4450 thank you so much for your help. I have done it right now and got it checked by my teacher. Thanks :)
     
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