1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Entropy, thermaldynamics

  1. Oct 5, 2011 #1
    1. The problem statement, all variables and given/known data

    A cylinder contains 1000mol o He gas at an initial temp o 2000k and initial pressure of 1MPa. The He gas is now cooled to a final temp o 500k in a reversible process in which the volume and pressure are constrained to vary as PV3 = constant. Assume that the He is a monatomic ideal gas. Denote the initial and final states of the gas by A and B, respectively.

    a) Find the initial volume VA of the gas

    b) use the 1st law o thermodynamics to show that

    dQin = (3/2)nRdT + (PAVA3dV)/V3

    c) eleminate P from the two process equations PV = nRT and PV3 = PAVA3

    and hence that

    blah blah blah

    d) Use dS/dQinrev/T to find the entropy change ΔS = SB - SA

    2. Relevant equations

    all given in the question


    3. The attempt at a solution

    I solved a) b) c) with no trouble, but i'm just uncertain about d)

    doing the integral i found that the change in entropy ΔS = -1.152x104 and i was wondering i this is reasonable, because i thought entropy is supposed to be ≥0.

    I thought to myself that the ΔSuniverse = 0 such that ΔS + ΔSsurrounding = 0

    would this be a good assumption?
     
  2. jcsd
  3. Oct 5, 2011 #2

    Mapes

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Yes; that's what "reversible" implies.
     
  4. Oct 5, 2011 #3
    derp :facepalm: thanks for the help
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Entropy, thermaldynamics
  1. Entropy and such (Replies: 12)

  2. Entropy and Gasoline (Replies: 6)

  3. Entropy concept (Replies: 3)

Loading...