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: 2nd Law of Thermo: Specific entropy

  1. Feb 6, 2012 #1
    1. The problem statement, all variables and given/known data

    A parcel of dry air is lifted isothermally such that its pressure decreases from 1000 hPa to 850 hPa. Calculate the change in specific entropy of the parcel.

    2. Relevant equations


    3. The attempt at a solution

    Using R=8.314 J/mol K

    And assuming n=1



    The problem is that's just the change in entropy. I need the change in specific entropy, which units are in J/g*K.

    The problem gives no information on the amount of mass within the parcel. Even if I had the mass, I'm not sure how I would find the specific entropy with it. What am I missing?

    edit: Nevermind. R is specific for dry air which is R=287 J/kg*K
    Last edited: Feb 6, 2012
  2. jcsd
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Can you offer guidance or do you also need help?
Draft saved Draft deleted