1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Work by an ideal gas in a thermodynamic cycle

  1. Feb 12, 2008 #1
    1. The problem statement, all variables and given/known data

    Two moles of an ideal gas are carried around the thermodynamic cycle shown in Fig. 18-29. The cycle consists of (1) an isothermal expansion A to B at a temperature of 700 K, with the pressure at A given by pA = 9 atm; (2) an isobaric compression B to C at PC = 4 atm; and (3) an isochoric pressure increase C A. What work is done by the gas per cycle? (See attached picture)

    2. Relevant equations

    pv=nRT

    W=pdv

    P=nRT/V


    3. The attempt at a solution

    W=nRT*ln(v2/v1)

    For Pa:
    9 atm= [2 mol*(.08205784 L*atm/k*mol)*700K]/V2

    For Pb:

    4 atm= [2 mol*(.08205784 L*atm/k*mol)*700K]/V1

    V2/V1= 4/9

    W=nRT(ln(4/9)) = 93.16 J (for A to B)

    Here is where I got stuck. I can't seem to find the work for B to C without having variables in the answer. Once I can find the work from B to C I can add the work quantities to find the total (and ignore the value for C to B because the total work with no volume change is zero).

    Any help in finding work from B to C would be appreciated.

    Thank you
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     

    Attached Files:

  2. jcsd
  3. Feb 12, 2008 #2

    George Jones

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    What is the pressure at C? What is the volume at C?
     
  4. Jan 28, 2011 #3
    You can use PV=nRT to find the volume at point A and C
    Then, pluge into the formula W=nRT*ln(V2/V1)
    Final subtract it with the area below that triangla W - 3*101325*(V2-V1)
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Work by an ideal gas in a thermodynamic cycle
Loading...