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Homework Help: Thermodynamics [IdealGases,W,Q, etc.] Much Help Needed-Detailed questions in descrip.

  1. Jan 10, 2013 #1
    I'm sorry I cannot conform to the default format Physicsforums.com; it is because I do not even know the first step to solving these sorts of problems, I don't know which equations to use which is a major problem. Here are the types of questions I require understanding.
    An ideal gas goes through three processes (A>B>C>[A]) (Triangular form) (PV Chart)
    How would I figure out The Q, W, and ΔU (internal energy) for A to B, B to C, C to A?
    On another graph using variables but this time with numerical values for P and V on the axis, how would I find the work done by a monatomic ideal gas as it expands from point A to point C along the path shown in the figure? Also, how much heat would be absorbed BY the gas during this process?
    Finding the net work, heat, and ΔU in another PV Graph with data on the axis-es?
    Calculating temperature, work, and/or internal energy in another PV Graph?
    Whether or not W, Q, or ΔU is positive(gained) or negative(released) in an ideal gas system as well as how those three (Q,W,..U) are related?

    I really wish to work on the problems myself, so I have only asked what procedures I should take.
    Here is a list of equations I have scavenged.

    ΔU = Won + Q

    ΔU = (3/2)nRΔT

    Won = -PΔV

    P1V1 = P2V2

    (P1V1)/T2 = (P2V2)/T2

    PV = nRT

    Is there any important equation that I am missing?
  2. jcsd
  3. Jan 10, 2013 #2


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  4. Jan 11, 2013 #3
    Re: Thermodynamics [IdealGases,W,Q, etc.] Much Help Needed-Detailed questions in desc

    A couple of errors it seems are to be found on the website but it has been very helpful so far I've read. Thank you ehild. :)
  5. Jan 12, 2013 #4

    Andrew Mason

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    Re: Thermodynamics [IdealGases,W,Q, etc.] Much Help Needed-Detailed questions in desc

    These problems are all about the First Law of Thermodynamics:

    ΔU = Q + W where W is the work done ON the gas. I prefer to use:

    Q = ΔU + W where W is the work done BY the gas.

    To determine the values, we would need to see the exact problem.

    Again, this requires application of the first law of thermodynamics.

    From the PV diagram you can determine T (if you are given n or an initial T) and W = PΔV (or -PΔV, depending on which version of the first law you are using). From T you can determine ΔU using ΔU = nCvΔT (you have given this equation for a monatomic ideal gas where Cv = 3R/2). From W and ΔU you can determine Q.

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