Chem 2 - The Second Law of Thermodynamics: Entropy and Heat IV

Chem 2 - The Second Law of Thermodynamics: Entropy and Heat IV

• 1.
  The Second Lawof 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 SecondLaw 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 Heatflows 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 Signof 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 ofFusion (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 GeneralizedPlot 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 PhaseTransitions 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 Signof S for Vaporization What is the sign of S for vaporization?
• 9.
  Predict the Signof 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 ThirdLaw and Standard Molar Entropy (S) (Pt 5)