Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Math Check on Thermo Problem

  1. Aug 26, 2010 #1
    1. The problem statement, all variables and given/known data

    2 moles of an ideal gas, P1 = 10 atm V1 = 5L, are taken reversibly in a clockwise direction around a circular path given by (V-10)^2 + (P-10)^2 = 25. All I have left to solve for is the minimum temperature.

    2. Relevant equations

    PV = nRT

    3. The attempt at a solution

    I found T1 = PV/nR = (10atm * 5L) / (2 moles * .08206) = 304.66K

    From the equation I found out that the center of the circle is (V, P) = (10,10) with a Radius of 5.

    From there I broke the circle up into 4 different sections starting at (5,10) and going clockwise. I found the max by saying that P = V and between (10, 15) and (15,10),

    (V-10)^2 = (P-10)^2 = 12.5
    P-10 = 3.536 Vmax = Pmax = 13.536 and Vmin = Pmin = 6.464

    PV = nRT

    Tmax = (13.536^2)/(2 moles * .08206) = 1116K (correct answer)
    Tmin = (6.464^2)/(2moles * .08206) = 255K (Answer:Tmin = 225K)

    Did I miscalculate where PV is a minimum between the section of (10,5) and (5,10) of the circle?
     
  2. jcsd
  3. Aug 26, 2010 #2

    presbyope

    User Avatar
    Gold Member

    No you're fine. Mathematically you are minimizing [itex]PV=(5\sin{t} +10)(5\cos{t}+10)[/itex]. Graphing is easiest. For any real data that's what you'd have to do anyway.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook