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Homework Help: What is the mass of the helium present - Thermodynamics

  1. Jan 10, 2006 #1
    A sample of helium behaves as an ideal gas as energy is added by heat at constant pressure from 273 K to 383 K. If the gas does 23.0 J of work, what is the mass of helium present?

    I tried this and think u use m=Q/c*change in T, but not sure where to go from there
     
  2. jcsd
  3. Jan 10, 2006 #2
    The expression for the work done by the gas is:
    [tex]dW=PdV[/tex]
    Since there is constan pressure we can write:
    [tex]V=\frac{nRT}{P}[/tex]
    [tex]dV=\frac{nR}{P}dT[/tex]
    So
    [tex]dW=nRdT[/tex]
    and
    [/tex]W=\int_{T_1}^{T_2}nRdT[/tex]
    Do the integral, use the molar mass of He to convert the # of moles of He to the mass, and then solve for the mass.
     
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