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Homework Help: Adiabatic expansion, isobaric return and a constant volume process at the end...

  1. Jun 29, 2017 #1
    1. The problem statement, all variables and given/known data
    1.0 mol sample of an ideal monatomic gas originally at a pressure of 1 atm undergoes a 3-step process as follows:

    It expands adiabatically from T1 = 588 K to T2 = 389 K

    It is compressed at constant pressure until its temperature reaches T3 K

    It then returns to its original pressure and temperature by a constant volume process.

    a. Plot these processes on a PV diagram

    b. Determine the temperature T3

    c. Calculate the change in internal energy, work done by the gas and heat added to the gas for each of these three processes

    d. Calculate the change in internal energy, work done by the gas and heat added to the gas for the complete cycle.

    2. Relevant equations

    I have included on my work sheet.

    3. The attempt at a solution
    Please see attached, I currently have a LATeX allergy ;-) I am stuck at the point of not knowing for sure if I have come to a logical conclusion. I have seen adiabatic charts before that have a second isotherm under the first. The wording of the problem leads me to believe that I have drawn the proper PV diagram. If this is the case, then part ii) would indicate that the gas should return to its initial volume, which means its getting compressed under constant pressure. If that is the case, the gas must be losing heat. At least that is what I posited. My next thought was to continue with Charles Law since pressure is constant. Have I got it right or have I wasted half a day and two pages?

    Thanks for any input.

    Attached Files:

  2. jcsd
  3. Jun 29, 2017 #2
    It's very difficult to read your uploaded files. Any chance of enlarging?
  4. Jun 29, 2017 #3
    I tried to upload the word file, but I guess it wasn't allowed. Let me try pdf.

    Attached Files:

    • 2.pdf
      File size:
      70.7 KB
  5. Jun 29, 2017 #4
    Thanks. So far, what you've done is OK. You can continue with Charles law, knowing that V3=V1. This will give you T3.
  6. Jun 29, 2017 #5
    That is a load off of my chest. I thought I was right, but with 1/2 a days work in this I didn't want to proceed with a false assumption. Thanks!!
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