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The Second Law of Thermodynamics: Entropy and Heat IV

The Second Law of Thermodynamics: Entropy and Heat IV

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The Second Law of Thermodynamics: Entropy and Heat IV

  1. 1. The Second Law of Thermodynamics: Entropy and Heat, plus Examples (Pt 4) By Shawn P. Shields, Ph.D. This work is licensed by Shawn P. Shields-Maxwell under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.
  2. 2. Recall: The Second Law of Thermodynamics The total entropy change for any spontaneous process is positive Positional disorder- The distribution of molecules (particles) in space (related to volume) Thermal disorder- The distribution of energy states among the particles (related to temperature)
  3. 3. Entropy and Heat Heat flows occurs spontaneously from hot objects to colder ones. Objects in contact will end up at the same temperature. “Heatflow" from http://www.chem1.com/acad/webtext/thermeq/TE1.html
  4. 4. Predicting the Sign of S for Changes in Temperature Entropy increases with increasing temperature. As heat is added to the system, the number of accessible energy states increases.
  5. 5. Example: Entropy of Fusion (Sfus) The entropy associated with fusion (melting) is ∆Sfus = qrev T = ∆Hfus T qrev is the heat associated with a reversible process.
  6. 6. Heating and Entropy “A Generalized Plot of Entropy versus Temperature for a Single Substance Absolute” from http://2012books.lardbucket.org/books/principle s-of-general-chemistry-v1.0m/s22-04-entropy- changes-and-the-third-.html Entropy increases steadily with T. Large jumps are observed during phase transitions.
  7. 7. S for Phase Transitions Fusion (melting): S increases as a substance melts. In the solid, particles are essentially fixed into place. As the substance melts, a larger number of positions are accessible to the molecules (in the liquid state)
  8. 8. Predict the Sign of S for Vaporization What is the sign of S for vaporization?
  9. 9. Predict the Sign of S for Vaporization What is the sign of S for vaporization? As the liquid vaporizes, more positions are available to the gas molecules. S is positive.
  10. 10. Next up… The Third Law and Standard Molar Entropy (S) (Pt 5)

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