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Thermal Processes

  1. Mar 18, 2008 #1
    [SOLVED] Thermal Processes

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

    With the pressure held constant at 240 kPa , 42 mol of a monatomic ideal gas expands from an initial volume of 0.75 meters cubed to a final volume of 2.0 meters cubed.

    a)How much work is done by the gas during expansion?
    b)What were the initial and final temperatures?
    c)what was the change in the internal energy of the gas?
    d)How much heat was added?

    I know the anwser for a) is 3.0*10^5
    i cant find the other three

    can someone please help
  2. jcsd
  3. Mar 18, 2008 #2

    Chi Meson

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    Where have you looked?
  4. Mar 18, 2008 #3

    Andrew Mason

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    Use ideal gas law: PV = nRT. You know P, V and n so just work out T for intial and final states.
    What is Cv for a monatomic gas? How is [itex]\Delta U[/itex] related to Cv and [itex]\Delta T[/itex]?
    Use first law: dQ = dU + dW

    As a short-cut, since it is a constant pressure process, you can just use: dQ = CpdT. What is Cp for a monatomic gas?


  5. Mar 18, 2008 #4
    the units for the first answer are Joules

    How do i wotk out the T for inital and final states
  6. Mar 18, 2008 #5
    the Cv for a monatomic gas is 12.465

    delta U is 3/2*n*R*deltaT
  7. Mar 18, 2008 #6
    Cp for a monatomic gas is 20.775
  8. Mar 18, 2008 #7


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    Use the ideal gas law PV=nRT like Andrew suggested in post #3. You were given all the information you need to solve this for T.
  9. Mar 18, 2008 #8
    For T i get 859.5 How do i get the inital temperature
  10. Mar 18, 2008 #9


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    You just use the ideal gas law twice. Once for the initial state (so before it expands), and once for the final state (after it expands).

    Be very careful with your units.
  11. Mar 18, 2008 #10
    thanks for all your help
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