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Homework Help: Pressure vs Vlume graph questions

  1. Mar 9, 2010 #1
    1. The problem statement, all variables and given/known data

    0.20 moles of a monatomic ideal gas is initially at a temperature of –23 0C.
    Call this state “A.” The gas is now compressed slowly and adiabatically to
    state “B” in which it has one third of its initial volume. Next it is isothermally
    expanded back to its initial volume in state “C.” Finally it undergoes a
    constant volume process that returns it to its initial state.

    a) Sketch this cyclic process with reasonable care on a PV diagram and
    label the three states—A, B, and C.

    b) Show that the temperature of state B is 247 0C.

    c) Find the heat input to the gas along each leg of the cycle—QAB, QBC,
    and QCA. [Note: Use the result of part b whether or not you got it!]

    d) Use the results of part c) and the first law of thermodynamics to find the
    net work done by the gas around the entire cycle.

    2. Relevant equations



    3. The attempt at a solution

    Part A) Note the attachment. Its a little crude but the two lines (ab) & (bc) are suppose to nice curves

    Part B) I'm not really sure what forumla to use here. Because the temp changes I know i cant use and of the PV formulas. Heres what I know...

    T_o = 250 Kelvin, T = 520 Kelvin, V = 1/3 V_o, Q = 0
     
  2. jcsd
  3. Mar 10, 2010 #2
    oops forgot the attachment.

    Should i be using

    PV - P_oV_o = Nk(T - T_o) and solve for T

    first i need to find P

    PV = P_oV_o ....P(1/3 V_o) = P_o V_o.... P = 3P_o

    3P(1/3V) - PV = Nk(T - 250) where N = .2*6.02E^23 & k = 1.38E^-23

    0 = NkT - NK250 this is not right what ami doin wrong
     

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