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: Thermodynamics Entropy Question

  1. Nov 17, 2013 #1
    1. The problem statement, all variables and given/known data

    45g of H2O(g) are condensed at 100 degrees C, and H2O(l) is cooled to 0 degrees C and then frozen to H2O solid. Find the Change in Entropy

    H2O(l): 4.2 J K-1g-1
    vaporization at 100 degrees C: 2258 J g-1;
    fusion at 0 degrees C: 334 J g

    2. Relevant equations

    3. The attempt at a solution
    q1=(45g)(2258J/g) = -101610J
    q2=(45g)(4.2J/K/g)(100K) = -18900J
    q3=(45g)(334J/g)= -15030J

    Total q=-135540J / 273.15K
    delta S = -496.2J/K

    I'm not sure if I did that right, can anybody double check? Thank you
    Last edited: Nov 17, 2013
  2. jcsd
  3. Nov 17, 2013 #2
    I think I solved my mistake, I'm not supposed to divide by T at the end, I need to do it for each step.

    So q1= -101610J/373.15K = -272.3J/K
    q2= 45gx4.2J/K/g x ln(273.15K/373.15K) = -58.96J/K
    q3= -15030J/273.15K = -55.02J/K

    Total Change in Entropy= -386.3J/K
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted