# The Second Law of Thermodynamics: Entropy and Heat IV

Lumen Learning
2 de Jun de 2016
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### The Second Law of Thermodynamics: Entropy and Heat IV

• 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. 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. 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. 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. 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. 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. 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. Predict the Sign of S for Vaporization What is the sign of S for vaporization?
• 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. Next up… The Third Law and Standard Molar Entropy (S) (Pt 5)