Accessible quantum statistical approach to molecular thermodynamics for first-year college chemistry students Bob Hanson and Susan Green St. Olaf College,
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accessible quantum statistical approach to molecular
thermodynamics for first-year college chemistry students
Bob Hanson and Susan Green
St. Olaf College, Northfield, MN
http://www.stolaf.edu/people/hansonrBCCE 18, July 21, 2004
Goals of this Presentation• VERY briefly describe the context of first-year chemistry at St. Olaf.
• Make a case for a molecular, probabilistic approach to introducing thermodynamics.
• Describe the challenge of introducing thermodynamics at the first-year level.
• Quickly run through the sequence.
• Share student feedback.
First-Year Chemistry At St. Olaf
Stoichiometrygas laws
pKa/pKb/Ksp
Stoichiometrygas laws
pKa/pKb/KspMolecular Structure
Bonding
ThermodynamicsElectrochemistry
Kinetics
MolecularStructure and
Bonding
Chemistry 125
Chemistry 121
Chemistry 123
Chemistry 126
FALL INTERIM SPRING
…for about 8 weeks we study thermo…
ThermodynamicsElectrochemistry
Kinetics
Chemistry 126
The Challenge: Alphabet Soup
internal energy, U
heat, q temperature, T
entropy, S enthalpy, H
work, w
heat capacity, C
free energy, Gequilibrium constant, K
reaction quotient, Q
Textbook X, chap. 6, p. 220
internal energy, U
heat, q temperature, T
entropy, S enthalpy, H
work, w
heat capacity, C
free energy, Gequilibrium constant, K
reaction quotient, Q
ΔU = q + w
Textbook X, chap. 6, p. 221
internal energy, U
heat, q temperature, T
entropy, S enthalpy, H
work, w
heat capacity, C
free energy, Gequilibrium constant, K
reaction quotient, Q
q = CΔT
Textbook X, chap. 6, p. 232
internal energy, U
heat, q temperature, T
entropy, S enthalpy, H
work, w
heat capacity, C
free energy, Gequilibrium constant, K
reaction quotient, Q
ΔH = q
internal energy, U
heat, q temperature, T
entropy, S enthalpy, H
work, w
heat capacity, C
free energy, Gequilibrium constant, K
reaction quotient, Q
Textbook X chap. 14, p. 689
Q = K ?
internal energy, U
heat, q temperature, T
entropy, S enthalpy, H
work, w
heat capacity, C
free energy, Gequilibrium constant, K
reaction quotient, Q
Textbook X chap. 18, p. 861
ΔS = q/T
internal energy, U
heat, q temperature, T
entropy, S enthalpy, H
work, w
heat capacity, C
free energy, Gequilibrium constant, K
reaction quotient, Q
Textbook X chap. 18, p. 873
ΔG = ΔH - TΔS
internal energy, U
heat, q temperature, T
entropy, S enthalpy, H
work, w
heat capacity, C
free energy, Gequilibrium constant, K
reaction quotient, Q
Textbook X chap. 18, p. 878
ΔG = ΔGo + RT ln Q
internal energy, U
heat, q temperature, T
entropy, S enthalpy, H
work, w
heat capacity, C
free energy, Gequilibrium constant, K
reaction quotient, Q
Textbook X chap. 18, p. 879
0 = ΔGo + RT ln K
It’s simple, really!
internal energy, U
heat, q temperature, T
entropy, S enthalpy, H
work, w
heat capacity, C
free energy, Gequilibrium constant, K
reaction quotient, Q
A simplified concept map:
internal energy, U
heat, q
temperature, Tentropy, S enthalpy, H
work, w
free energy, G
equilibrium constant, Kreaction quotient, Q
Problems with the standard approach:This is not a particularly molecular approach to thermodynamics.
The standard approach fails to make the connection between entropy and reaction quotient.
This approach largely ignores the probabilistic nature of chemical reactions.
This approach completely ignores modern quantum mechanics.
internal energy, U
heat, q
temperature, Tentropy, S enthalpy, H
work, w
free energy, G
equilibrium constant, Kreaction quotient, Q
The IMT approach:
1. We describe internal energy, work, heat, entropy, enthalpy, and temperature in terms of molecular systems with discrete quantum energy levels.
internal energy, U
heat, q
temperature, Tentropy, S enthalpy, H
work, w
free energy, G
equilibrium constant, Kreaction quotient, Q
The IMT approach:
2. We use probability as a foundation for discussions of chemical reactions, equilibrium, entropy, temperature, and enthalpy.
internal energy, U
heat, q
temperature, Tentropy, S enthalpy, H
work, w
free energy, G
equilibrium constant, Kreaction quotient, Q
The IMT approach:
3. The connecting points are entropy, temperature, and enthalpy, which are discussed in terms of system and surroundings.
internal energy, U
heat, q
temperature, Tentropy, S enthalpy, H
work, w
free energy, G
equilibrium constant, Kreaction quotient, Q
systemsurroundings
system system
The IMT approach:
4. We make strong connections between entropy and reaction quotient and between temperature and equilibrium constants.
internal energy, U
heat, q
temperature, Tentropy, S enthalpy, H
work, w
free energy, G
equilibrium constant, Kreaction quotient, Q
Why this approach?
-- four arguments come to mind…
The argument: molecular…
1. Chemistry is a modern molecular science.
internal energy, U
heat, q
temperature, Tentropy, S enthalpy, H
work, w
free energy, G
equilibrium constant, Kreaction quotient, Q
The argument: …quantization…
2. Discussing thermodynamics without quantized energy ignores about 100 years of modern physics and chemistry.
internal energy, U
heat, q
temperature, Tentropy, S enthalpy, H
work, w
free energy, G
equilibrium constant, Kreaction quotient, Q
The argument: …involving probability
3. Simple ideas of probability are intellec-tually accessible and intriguing for entry-level college students.
internal energy, U
heat, q
temperature, Tentropy, S enthalpy, H
work, w
free energy, G
equilibrium constant, Kreaction quotient, Q
The argument: …and it’s fun.
4. Besides, it’s great fun teaching thermo-dynamics this way!
internal energy, U
heat, q
temperature, Tentropy, S enthalpy, H
work, w
free energy, G
equilibrium constant, Kreaction quotient, QHigh school students at Eastview HS playing the Boltzmann game.
...we start with cards and dice, quickly finding that K derives strictly from probability…
internal energy, U
heat, q
temperature, Tentropy, S enthalpy, H
work, w
free energy, G
equilibrium constant, Kreaction quotient, Q
…we bring in the distribution of “quanta” of energy and its relation to temperature…
internal energy, U
heat, q
temperature, Tentropy, S enthalpy, H
work, w
free energy, G
equilibrium constant, Kreaction quotient, Q
…we discuss how energy can be “stored” in real chemical systems…
internal energy, U
heat, q
temperature, Tentropy, S enthalpy, H
work, w
free energy, G
equilibrium constant, Kreaction quotient, Q
…we provide a “microscopic” perspective for discussing work and heat…
internal energy, U
heat, q
temperature, Tentropy, S enthalpy, H
work, w
free energy, G
equilibrium constant, Kreaction quotient, Q
…we talk about bond dissociation energies in relation to internal energy…
internal energy, U
heat, q
temperature, Tentropy, S enthalpy, H
work, w
free energy, G
equilibrium constant, Kreaction quotient, Q
...we discuss the effect of temperature in terms of population of energy levels…
internal energy, U
heat, q
temperature, Tentropy, S enthalpy, H
work, w
free energy, G
equilibrium constant, Kreaction quotient, Q
…we bring in entropy as k ln W and show that for a Boltzmann distribution ΔS = q/T…
internal energy, U
heat, q
temperature, Tentropy, S enthalpy, H
work, w
free energy, G
equilibrium constant, Kreaction quotient, Q
…we discover the basis of reaction quotients and consider system and surroundings…
internal energy, U
heat, q
temperature, Tentropy, S enthalpy, H
work, w
free energy, G
equilibrium constant, Kreaction quotient, Q
system
surroundings
…enthalpy is seen as a measure of the entropy change of the surroundings…
internal energy, U
heat, q
temperature, Tentropy, S enthalpy, H
work, w
free energy, G
equilibrium constant, Kreaction quotient, Q
systemsurroundings
…now we are ready for free energy…
internal energy, U
heat, q
temperature, Tentropy, S enthalpy, H
work, w
free energy, G
equilibrium constant, Kreaction quotient, Q
…and we can see how free energy ties it all together…
internal energy, U
heat, q
temperature, Tentropy, S enthalpy, H
work, w
free energy, G
equilibrium constant, Kreaction quotient, Q
…lots of fun demos and applications…
internal energy, U
heat, q
temperature, Tentropy, S enthalpy, H
work, w
free energy, G
equilibrium constant, Kreaction quotient, Q
…later, we come back for a brief discussion of free energy in relation to electrochemistry.
internal energy, U
heat, q
temperature, Tentropy, S enthalpy, H
work, w
free energy, G
equilibrium constant, Kreaction quotient, Q
…for about 8 weeks we study thermo…
…now for what the students say…
ThermodynamicsElectrochemistry
Kinetics
Chemistry 126
Feedback from students:• Chemistry 126 is probably the most challenging and rewarding course I took this past year. I don't think about the world the same way.
• I enjoyed it and learned way more about the WORLD than I thought I would.
• it was fun, i learned a lot, and look forward and feel prepared for orgo next year.
• i learned a lot and am glad i took the course. i had to work very hard but it was worth it
Feedback from students:• I enjoyed this class very much and I feel that I learned a lot. It was a completely different view of chemistry from what I got in high school, especially relating to the emphasis on probability.
• i absolutely loved this course! it has answered a lot of questions that i've had for years... thanks for a great course.
• Chem 126 was at times the most frustrating, challenging, and exciting class that I have ever had. Even if I end up not being a science major, I will never consider this class a waste of time. Overall, I think that this class was very valuable to my college experience thus far.
• I liked it, and I'm glad I've survived.
Conclusions:
• Probability can provide an accessible entry point into thermodynamics even at the first-year level.
• Students at the first-year level are ready to think about the basics of energy quantization and its consequences.
• Introducing probability and quantization takes time, but it’s fun, and it’s worth it.
Acknowledgments:
• The IMT approach is based on earlier approaches by Leonard Nash, William Davies, and Richard Dickerson.
• We wish to thank all of our fine colleagues over the past five years who have ventured forth with us so courageously.
• We appreciate all the feedback we have gotten from St. Olaf College and Macalester College students.
Thank you!
feedback appreciated
Bob Hanson and Susan Green
St. Olaf College, Northfield, MN
http://www.stolaf.edu/people/hansonrBCCE 18, July 19, 2004
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