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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
    dS=dq/T


    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
     
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