Loading...

CHEM105: Physical Chemistry I

Unit 6: Spontaneous Changes, Chemical Potential, and Equilibrium   A chemical system is in equilibrium when the activities and concentrations of the reactants and products do not change with time. This usually comes about when the forward reaction rate and the reverse reaction rate are the same. In this situation, known as dynamic equilibrium, chemical reactions are still in progress, and specific atoms move between molecules, but the total amount of the various chemical species remains the same. As we will see, a chemical system in dynamic equilibrium tends to remain in equilibrium even when it is disturbed by a change in the conditions associated with the original equilibrium. Equilibrium is associated with a global minimum in the relevant free energy function. Metastability is associated with local minima in the free energy that are separated from the global minimum by activation energy barriers. Many chemical processes lead to metastable states rather than an equilibrium state, thus allowing for the possibility of further, spontaneous change (in the direction of a true, thermodynamic equilibrium state). Controlling and changing chemical equilibria is perhaps the most important skill that a chemist must develop.

Unit 6 Time Advisory
Completing this unit should take approximately 25.5 hours.

☐  Subunit 6.1: 8 hours
☐  Subunit 6.2: 5 hours
☐  Subunit 6.3: 5 hours
☐  Subunit 6.4: 1 hour
☐  Subunit 6.5: 5 hours
☐  Subunit 6.6: 1 hour
☐  Subunit 6.7: 30 minutes

Unit6 Learning Outcomes
Upon successful completion of this unit, you should be able to: - define the Gibbs and Helmholtz energies, and calculate these energies for various state changes in chemical systems; - describe the relationship between spontaneity of reactions and Gibbs free energy; - define chemical potential and its relationship to free energy in multicomponent systems; - calculate DG for multicomponent systems; - describe Le Chatelier’s principle; - define chemical equilibrium, and calculate it; - describe the relationship among T, P, and equilibrium; - calculate K for different conditions; and - apply equilibrium principles to drug discovery.

6.1 Spontaneous Changes in Chemical Systems   - Reading: Dr. Howard DeVoe’s Thermodynamics and Chemistry (2nd ed.): “Chapter 5: Thermodynamic Potentials” Link: Dr. Howard DeVoe’s Thermodynamics and Chemistry (2nd ed.): “Chapter 5: Thermodynamic Potentials” (PDF)

 Instructions: Navigate to chapter 5, starting on page 135, and read
the chapter through page 149. Pay special attention to section 5.8,
titled “Criteria for Spontaneity,” beginning on page 145. Also, be
sure to work through the problems presented at the end of the
chapter. Note that the criteria for spontaneous change in the
thermodynamic state of a system depend on both the compositional and
P-V-T (physical) variables of the system, as well as whether the
system is isolated, closed, or open with respect to its boundary
with surroundings. Pay very close attention to how the criteria for
spontaneous change are expressed in terms of changes in various
thermodynamic state functions.  

 Reading this material should take approximately 4 hours.  

 Terms of Use: This resource is licensed under a [Creative Commons
Attribution-NonCommercial-NoDervis 3.0 Unported
License](http://creativecommons.org/licenses/by-nc-nd/3.0/).  
  
  • Optional: Dr. Stephen Lower’s Chem1 Virtual Textbook: “Thermodynamics of Chemical Equilibrium: All about Entropy and Free Energy (Sections 1-3)” Link: Dr. Stephen Lower’s Chem1 Virtual Textbook: “Thermodynamics of Chemical Equilibrium: All about Entropy and Free Energy (Sections 1-3)” (HTML)

    Instructions: Read the material presented in sections 1-3 (from “Energy spreading drives spontaneous change” to “The Second Law and the availability of energy”) of the webpage, including all the hyperlinked material within each section. Note that this reading is optional, but it will provide you with an excellent review of the thermodynamic concepts and principles you have learned thus far (and will most likely deepen your understanding of thermodynamics as an applied science). If you choose to complete this reading, you may also wish to peruse the supplementary material provided via the related links found at the bottom of the webpage.

    Terms of Use: This resource is licensed under a Creative Commons Attribution-NonCommercial-NoDervis 3.0 Unported License.
     

  • Lecture: The Massachusetts Institute of Technology OpenCourseWare: Dr. Moungi Bawendi and Dr. Keith Nelson’s “Lecture 12: Criteria for Spontaneous Change” Link: The Massachusetts Institute of Technology OpenCourseWare: Dr. Moungi Bawendi and Dr. Keith Nelson’s “Lecture 12: Criteria for Spontaneous Change”

    Also available in:

    iTunesU

    MP4

    Instructions: Watch the video (approximately 48 minutes in length) to learn about how we judge whether a system is moving spontaneously toward an equilibrium state or is already there. You also will learn about the Gibbs and Helmholtz free energies, which are ways of predicting spontaneity under different conditions. 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.

  • Reading: McGill University: Dr. David Ronis’s “Thermodynamic Stability: Free Energy and Chemical Equilibrium” (PDF) Link: McGill University: Dr. David Ronis’s “Thermodynamic Stability: Free Energy and Chemical Equilibrium” (PDF)

    Instructions: Read the online PDF of Dr. Ronis’s handout. Read the handout to acquire an understanding of the thermodynamic criteria for a spontaneous change of state in a material system.

    Reading this material should take approximately 3 hours.

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

6.2 Gibbs Free Energy   - Lecture: Massachusetts Institute of Technology OpenCourseWare: Dr. Moungi Bawendi and Dr. Keith Nelson’s “Lecture 13: Gibbs Free Energy” Link: Massachusetts Institute of Technology OpenCourseWare: Dr. Moungi Bawendi and Dr. Keith Nelson’s “Lecture 13: Gibbs Free Energy”

 Also available in:  

[iTunesU](http://ocw.mit.edu/courses/chemistry/5-60-thermodynamics-kinetics-spring-2008/video-lectures/lecture-13-gibbs-free-energy/)  

[MP4](http://ocw.mit.edu/courses/chemistry/5-60-thermodynamics-kinetics-spring-2008/video-lectures/lecture-13-gibbs-free-energy/)  

 Instructions: Watch the video (approximately 50 minutes in length)
to learn about what is arguably the most important thermodynamic
function in chemistry: the Gibbs free energy. This function helps us
determine the direction of spontaneity in any chemical reaction. You
can find the lecture notes for this video here (PDF).  

 Watching this lecture should take you 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: Dr. Howard DeVoe’s Thermodynamics and Chemistry (2nd ed.): “Chapter 5: Thermodynamic Potentials” Link: Dr. Howard DeVoe’s Thermodynamics and Chemistry (2nd ed.): “Chapter 5: Thermodynamic Potentials” (PDF)

    Instructions: Navigate to chapter 5, titled “Thermodynamic Potentials,” starting on page 135, and read the chapter through page

    1. Note that this chapter has been assigned earlier in this course; as you read this time, carefully review how the thermodynamic free-energy state functions (i.e., the Helmholtz and Gibbs functions) are defined and used in thermodynamic analyses and calculations.

    Reading this material should take approximately 2 hours.

    Terms of Use: This resource is licensed under a Creative Commons Attribution-NonCommercial-NoDervis 3.0 Unported License.
     

  • Reading: Dr. Stephen Lower’s Chem1 Virtual Textbook: “Thermodynamics of Chemical Equilibrium: All about Entropy and Free Energy (Sections 4-6)” Link: Dr. Stephen Lower’s Chem1 Virtual Textbook: “Thermodynamics of Chemical Equilibrium: All about Entropy and Free Energy (Sections 4-6)” (HTML)

    Instructions: Read sections 4-6 of the webpage (from “Free energy and the Gibbs function” to “Some applications of entropy and free energy”), including all the hyperlinked material within each section. The subject matter presented in sections 4-6 assumes familiarity with the material in sections 1-3, which you read in an earlier assignment in this course. You may wish to refer back to this resource as you progress through the remaining units of this course, as it provides an excellent review of important thermodynamic concepts and principles.

    Reading this material should take approximately 2 hours.

    Terms of Use: This resource is licensed under a Creative Commons Attribution-NonCommercial-NoDervis 3.0 Unported License.
     

6.3 Multicomponent Systems and Chemical Potential   - Lecture: Massachusetts Institute of Technology OpenCourseWare: Dr. Moungi Bawendi and Dr. Keith Nelson’s “Lecture 14: Multicomponent Systems, Chemical Potential” Link: Massachusetts Institute of Technology OpenCourseWare: Dr. Moungi Bawendi and Dr. Keith Nelson’s “Lecture 14: Multicomponent Systems, Chemical Potential”

 Also available in:  

[iTunesU](http://ocw.mit.edu/courses/chemistry/5-60-thermodynamics-kinetics-spring-2008/video-lectures/lecture-14-multicomponent-systems-chemical-potential/)  

[MP4](http://ocw.mit.edu/courses/chemistry/5-60-thermodynamics-kinetics-spring-2008/video-lectures/lecture-14-multicomponent-systems-chemical-potential/)  

 Instructions: Watch the video (approximately 47 minutes in length)
to learn about how to calculate the Gibbs free energy per mole of
systems with multiple components. 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/).

6.4 Le Chatelier’s Principle   - Lecture: Academic Earth: The University of California at Berkeley: Dr. Angelica Stacy’s “How Pushy: Le Chatelier’s Principle” Link: Academic Earth: The University of California at Berkeley: Dr. Angelica Stacy’s “How Pushy: Le Chatelier’s Principle” (Adobe Flash)

 Instructions: Watch the video (approximately 50 minutes in length)
to learn about how Le Chatelier’s principle can qualitatively
predict the shift in equilibrium under different kinds of
perturbations.  

 Watching this lecture should take approximately 1 hour.  

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

6.5 Chemical Equilibrium   - Lecture: Massachusetts Institute of Technology OpenCourseWare: Dr. Moungi Bawendi and Dr. Keith Nelson’s “Lecture 15: Chemical Equilibrium” Link: Massachusetts Institute of Technology OpenCourseWare: Dr. Moungi Bawendi and Dr. Keith Nelson’s “Lecture 15: Chemical Equilibrium”

 Also available in:  

[iTunesU](http://ocw.mit.edu/courses/chemistry/5-60-thermodynamics-kinetics-spring-2008/video-lectures/lecture-15-chemical-equilibrium/)  

[MP4](http://ocw.mit.edu/courses/chemistry/5-60-thermodynamics-kinetics-spring-2008/video-lectures/lecture-15-chemical-equilibrium/)  

 Instructions: Watch the video (approximately 51 minutes in length)
to derive the relationship among Gibbs free energy, chemical
potential, and equilibrium. 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: Dr. Howard DeVoe’s Thermodynamics and Chemistry (2nd ed.): “Chapter 11: Reactions and Other Chemical Processes” and “Chapter 12: Equilibrium Conditions in Multicomponent Systems” Link: Dr. Howard DeVoe’s Thermodynamics and Chemistry (2nd ed.): “Chapter 11: Reactions and Other Chemical Processes” and “Chapter 12: Equilibrium Conditions in Multicomponent Systems” (PDF)

    Instructions: Navigate to chapter 11, starting on page 303. Read all of chapters 11 and 12, through page 418. Be sure to work through all the practice problems at the end of these chapters. Note that chapter 12 has been assigned earlier in this course; as you read this time, focus on changes in the thermodynamic properties that occur as a consequence of changes in compositional variables attendant to a chemical reaction (as opposed to changes in physical variables).

    Reading this material should take approximately 4 hours.

    Terms of Use: This resource is licensed under a Creative Commons Attribution-NonCommercial-NoDervis 3.0 Unported License.
       

6.6 The Effect of Temperature and Pressure on Chemical Equilibrium   - Lecture: Massachusetts Institute of Technology OpenCourseWare: Dr. Moungi Bawendi and Dr. Keith Nelson’s “Lecture 16: Temperature, Pressure and Kp” Link: Massachusetts Institute of Technology OpenCourseWare: Dr. Moungi Bawendi and Dr. Keith Nelson’s “Lecture 16: Temperature, Pressure and Kp

 Also available in:  

[iTunesU](http://ocw.mit.edu/courses/chemistry/5-60-thermodynamics-kinetics-spring-2008/video-lectures/lecture-16-temperature-pressure-and-kp/)  

[MP4](http://ocw.mit.edu/courses/chemistry/5-60-thermodynamics-kinetics-spring-2008/video-lectures/lecture-16-temperature-pressure-and-kp/)  

 Instructions: Watch the video (approximately 52 minutes in length)
to learn how to express the equilibrium constant in two ways:
K<sub>p</sub>, which is independent of total pressure; and
K<sub>x</sub>, which depends on pressure. You also will see a more
quantitative presentation of Le Chatelier’s principle, as well as
assess how varying temperature, pressure, and volume affect the
chemical potential and, thus, the equilibrium position of a system.
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/).

6.7 Biological Applications of Equilibrium   - Lecture: Massachusetts Institute of Technology OpenCourseWare: Dr. Moungi Bawendi and Dr. Keith Nelson’s “Lecture 17: Equilibrium: Application to Drug Design” Link: Massachusetts Institute of Technology OpenCourseWare: Dr. Moungi Bawendi and Dr. Keith Nelson’s “Lecture 17: Equilibrium: Application to Drug Design”

 Also available in:  

[iTunesU](http://ocw.mit.edu/courses/chemistry/5-60-thermodynamics-kinetics-spring-2008/video-lectures/lecture-17-equilibrium-application-to-drug-design/)  

[MP4](http://ocw.mit.edu/courses/chemistry/5-60-thermodynamics-kinetics-spring-2008/video-lectures/lecture-17-equilibrium-application-to-drug-design/)  

 Instructions: Watch the video (approximately 32 minutes in length)
to see an interesting modern application of equilibrium
thermodynamics in the field of drug discovery You can find the
lecture notes for this video here (PDF).  

 Watching this lecture should take approximately 30 minutes.  

 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/).