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!

Homework Help: Entropy of vaporisation

  1. May 3, 2017 #1
    1. The problem statement, all variables and given/known data

    5 moles of liquid argon undergoes vaporization at its normal boiling point (87.5 K) and the resulting argon gas is subsequently heated to 150 K under constant volume conditions. Calculate the change of entropy for this process. The standard enthalpy change of vaporization, ∆ ⊖ is +6.5 kJ mol-1 for argon. Treat gaseous argon as an ideal gas in your calculations.
    2. Relevant equations
    ΔS= ΔvapH/ T
    ΔS= q/T
    ΔS= nCvln(Tf/Ti)
    3. The attempt at a solution
    For entropy of vaporisation at 87.5 K
    ΔvapH= 6.5 kJ mol-1 for one mole ∴ 5 moles = (6.5⋅5)⋅1000= 32500 J mol-1
    Using Trouton's Rule ΔS1= 32500/87.5 = 371.43 J K-1

    Entropy from 87.5 K to 150 K
    ΔS2= 5⋅ 3/2R⋅ ln(150/87.5)
    ΔS2= 33.61 J K-1

    Total entropy change= ΔSsys= ΔS1 + ΔS2
    ΔSsys= 371.43 + 33.61 = 405.04 J K-1
  2. jcsd
  3. May 3, 2017 #2
    Your methodology looks correct. I haven't checked your arithmetic.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted