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CHEM105: Physical Chemistry I

Unit 5: The Third Law of Thermodynamics   The third law of thermodynamics is the odd man out, so to speak. The 0th (zeroth) law states that two bodies having the same temperature as a third have the same temperature as each other; the first law states that energy is conserved; and the second law states that heat cannot flow from a cold object to a hot object. These principles seem reasonably clear, although not beyond dispute. However, the third law is not as straightforward. It states that as a system approaches absolute zero, the entropy of the system, in turn, approaches a minimum value. However, despite the fact that the interpretation of the third law becomes rather confusing when quantum effects are included, there is no experimental example or reasonable theoretical result that violates the third law.

Unit 5 Time Advisory
Completing this unit should take approximately 9 hours.

☐  Subunit 5.1: 7 hours
☐  Subunit 5.2: 2 hours

Unit5 Learning Outcomes
Upon successful completion of this unit, you should be able to: - state the third law of thermodynamics; - define absolute entropy; and - define and calculate the entropy of mixing.

5.1 Fundamental Equation, Absolute Entropy, and the Third Law   - Lecture: The Massachusetts Institute of Technology OpenCourseWare: Dr. Moungi Bawendi and Dr. Keith Nelson’s “Lecture 11: Fundamental Equation, Absolute S, Third Law” Link: The Massachusetts Institute of Technology OpenCourseWare: Dr. Moungi Bawendi and Dr. Keith Nelson’s “Lecture 11: Fundamental Equation, Absolute S, Third Law”

 Also available in:  

[iTunesU](http://ocw.mit.edu/courses/chemistry/5-60-thermodynamics-kinetics-spring-2008/video-lectures/lecture-11-fundamental-equation-absolute-s-third-law/)  

[MP4](http://ocw.mit.edu/courses/chemistry/5-60-thermodynamics-kinetics-spring-2008/video-lectures/lecture-11-fundamental-equation-absolute-s-third-law/)  

 Instructions: Watch the video (approximately 52 minutes long),
which describes the third law of thermodynamics and the definition
of absolute entropy. Although we can never reach absolute zero of
temperature, it is an important reference point for defining an
absolute entropy scale. You can find the lecture notes for this
video here (PDF).  

 Watching this lecture should take approximately 1 hour.  

 Terms of Use: This resource is licensed under a [Creative Commons
Attribution-NonCommercial-ShareAlike 3.0 United States
license](http://creativecommons.org/licenses/by-nc-sa/3.0/us/).
  • Reading: The University of Windsor: Introductory Physical Chemistry: Dr. Rob Schurko’s Course Notes: “Lecture 12: Entropy Changes and Processes” Link: The University of Windsor: Introductory Physical Chemistry: Dr. Rob Schurko’s Course Notes: “Lecture 12: Entropy Changes and Processes” (PDF)

    Instructions: Read Dr. Schurko’s course notes. Read the set of notes, but pay special attention to the first part, which deals with the third law of thermodynamics.

    Reading this material should take approximately 1.5 hours.

    Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

  • Reading: McGill University: Dr. David Ronis’s “Entropy Calculations and the Third Law of Thermodynamics” Link: McGill University: Dr. David Ronis’s “Entropy Calculations and the Third Law of Thermodynamics” (PDF)

    Instructions: Read the online PDF of Dr. Ronis’s handout. This reading gives you a short, concise description of the third law of thermodynamics. It also presents several examples of how absolute third-law entropies are determined.

    Reading this material should take approximately 1.5 hours.

    Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

  • Reading: Dr. Howard DeVoe’s Thermodynamics and Chemistry (2nd ed.): “Chapter 6: The Third Law and Cryogenics” Link: Dr. Howard DeVoe’s Thermodynamics and Chemistry (2nd ed.): “Chapter 6: The Third Law and Cryogenics” (PDF)

5.2 Entropy of Mixing   - Reading: The University of Notre Dame OpenCourseWare: Dr. Joseph M. Powers’s Lecture Notes on Thermodynamics: “Chapter 8: Entropy” Link: The University of Notre Dame OpenCourseWare: Dr. Joseph M. Powers’s Lecture Notes on Thermodynamics: “Chapter 8: Entropy (Section 8.8)” (PDF)

 Instructions: Read and review chapter 8, which has been assigned
earlier in this course. As you read this time, focus specifically on
section 8.8, titled “Entropy of thermo-mechanical mixing,” beginning
on page 261. This section of the text focuses on the
entropy-of-mixing phenomenon. The entropy-of-mixing phenomenon
accounts for the spontaneous mixing of two or more substances under
conditions in which the mixing process is isoenergetic.  

 Reading this material should take approximately 2 hours.  

 Terms of Use: This resource is licensed under a [Creative Commons
Attribution 2.5 Generic
license](http://creativecommons.org/licenses/by/2.5/).