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/hansonr
BCCE 18, July 21, 2004
Goals of this Presentation
• VERY briefly describe the context of
first-year chemistry at St. Olaf.
• Describe the challenge of introducing
thermodynamics at the first-year level.
• Make a case for a molecular, probabilistic
approach to introducing thermodynamics.
• Quickly run through the sequence.
• Share student feedback.
First-Year Chemistry At St. Olaf
Stoichiometry
gas laws
pKa/pKb/Ksp
Chemistry 121
Molecular
Structure and
Bonding
Chemistry 123
Stoichiometry
gas laws
pKa/pKb/Ksp
Molecular Structure
Bonding
Thermodynamics
Electrochemistry
Kinetics
Chemistry 126
Chemistry 125
FALL
INTERIM
SPRING
…for about 8 weeks we study thermo…
Thermodynamics
Electrochemistry
Kinetics
Chemistry 126
The Challenge: Alphabet Soup
heat capacity, C
internal energy, U
work, w
heat, q
entropy, S
temperature, T
enthalpy, H
reaction quotient, Q
free energy, G
equilibrium constant, K
Textbook X, chap. 6, p. 220
heat capacity, C
internal energy, U
work, w
heat, q
entropy, S
temperature, T
enthalpy, H
reaction quotient, Q
free energy, G
equilibrium constant, K
ΔU = q + w
Textbook X, chap. 6, p. 221
heat capacity, C
internal energy, U
work, w
heat, q
entropy, S
temperature, T
enthalpy, H
reaction quotient, Q
free energy, G
equilibrium constant, K
q = CΔT
Textbook X, chap. 6, p. 232
heat capacity, C
internal energy, U
work, w
heat, q
entropy, S
temperature, T
enthalpy, H
reaction quotient, Q
free energy, G
equilibrium constant, K
ΔH = q
Textbook X chap. 14, p. 689
heat capacity, C
internal energy, U
work, w
heat, q
entropy, S
temperature, T
enthalpy, H
reaction quotient, Q
free energy, G
equilibrium constant, K
?
Q=K
Textbook X chap. 18, p. 861
heat capacity, C
internal energy, U
work, w
heat, q
entropy, S
temperature, T
enthalpy, H
reaction quotient, Q
free energy, G
equilibrium constant, K
ΔS = q/T
Textbook X chap. 18, p. 873
heat capacity, C
internal energy, U
work, w
heat, q
entropy, S
temperature, T
enthalpy, H
reaction quotient, Q
free energy, G
equilibrium constant, K
ΔG = ΔH - TΔS
Textbook X chap. 18, p. 878
heat capacity, C
internal energy, U
work, w
heat, q
entropy, S
temperature, T
enthalpy, H
reaction quotient, Q
free energy, G
equilibrium constant, K
ΔG = ΔGo + RT ln Q
Textbook X chap. 18, p. 879
heat capacity, C
internal energy, U
work, w
heat, q
entropy, S
temperature, T
enthalpy, H
reaction quotient, Q
free energy, G
equilibrium constant, K
0 = ΔGo + RT ln K
It’s simple, really!
heat capacity, C
internal energy, U
work, w
heat, q
entropy, S
temperature, T
enthalpy, H
reaction quotient, Q
free energy, G
equilibrium constant, K
A simplified concept map:
internal energy, U
work, w
entropy, S
heat, q
temperature, T
enthalpy, H
free energy, G
reaction quotient, Q
equilibrium constant, K
Problems with the standard approach:
This is not a particularly molecular
approach to thermodynamics.
internal energy, U
The standard approach fails
work, w
to make the connection
between entropy and
reaction quotient.
entropy, S
This approach largely
ignores the probabilistic
nature of chemical reactions.
heat, q
temperature, T
enthalpy, H
free energy, G
This approach completely
ignores modern quantum reaction quotient, Q
mechanics.
equilibrium constant, K
The IMT approach:
1. We describe internal
energy, work, heat,
entropy, enthalpy, and
work, w
temperature in terms of
molecular systems
with discrete quantum
entropy, S
energy levels.
internal energy, U
heat, q
temperature, T
enthalpy, H
free energy, G
reaction quotient, Q
equilibrium constant, K
The IMT approach:
internal energy, U
work, w
2. We use probability
as a foundation for
discussions of
chemical reactions,
equilibrium, entropy,
temperature, and
enthalpy.
entropy, S
heat, q
temperature, T
enthalpy, H
free energy, G
reaction quotient, Q
equilibrium constant, K
The IMT approach:
internal energy, U
3. The connecting
points are entropy,
temperature, and
enthalpy, which are
discussed in terms
of system and
surroundings.
work, w
heat, q
surroundings
entropy, S
system
enthalpy, H
temperature, T
system
system
free energy, G
reaction quotient, Q
equilibrium constant, K
The IMT approach:
internal energy, U
work, w
4. We make strong
connections between
entropy and reaction
entropy, S
quotient and between
temperature and
equilibrium constants.
heat, q
temperature, T
enthalpy, H
free energy, G
reaction quotient, Q
equilibrium constant, K
Why this approach?
-- four arguments come to
mind…
The argument: molecular…
1. Chemistry is a
modern molecular
science.
internal energy, U
work, w
entropy, S
heat, q
temperature, T
enthalpy, H
free energy, G
reaction quotient, Q
equilibrium constant, K
The argument: …quantization…
2. Discussing
thermodynamics
without quantized
energy ignores about
100 years of modern
physics and chemistry.
internal energy, U
work, w
entropy, S
heat, q
temperature, T
enthalpy, H
free energy, G
reaction quotient, Q
equilibrium constant, K
The argument: …involving
probability
3. Simple ideas of
probability are intellectually accessible and
intriguing for entry-level
college students.
internal energy, U
work, w
entropy, S
heat, q
temperature, T
enthalpy, H
free energy, G
reaction quotient, Q
equilibrium constant, K
The argument: …and it’s fun.
4. Besides, it’s great fun
teaching thermodynamics this way!
internal energy, U
work, w
entropy, S
heat, q
temperature, T
enthalpy, H
free energy, G
High school students at
Eastview HS playing the
Boltzmann game.
reaction quotient, Q
equilibrium constant, K
www.stolaf.edu/depts/chemistry/imt “concept index”
...we start with cards and dice, quickly finding
that K derives strictly from probability…
internal energy, U
work, w
entropy, S
heat, q
temperature, T
enthalpy, H
free energy, G
reaction quotient, Q
equilibrium constant, K
…we bring in the distribution of “quanta” of
energy and its relation to temperature…
internal energy, U
work, w
entropy, S
heat, q
temperature, T
enthalpy, H
free energy, G
reaction quotient, Q
equilibrium constant, K
…we discuss how energy can be “stored” in real
chemical systems…
internal energy, U
work, w
entropy, S
heat, q
temperature, T
enthalpy, H
free energy, G
reaction quotient, Q
equilibrium constant, K
…we provide a “microscopic” perspective for
discussing work and heat…
internal energy, U
work, w
entropy, S
heat, q
temperature, T
enthalpy, H
free energy, G
reaction quotient, Q
equilibrium constant, K
…we talk about bond dissociation energies in
relation to internal energy…
internal energy, U
work, w
entropy, S
heat, q
temperature, T
enthalpy, H
free energy, G
reaction quotient, Q
equilibrium constant, K
...we discuss the effect of temperature in terms
of population of energy levels…
internal energy, U
work, w
entropy, S
heat, q
temperature, T
enthalpy, H
free energy, G
reaction quotient, Q
equilibrium constant, K
…we bring in entropy as k ln W and show that
for a Boltzmann distribution ΔS = q/T…
internal energy, U
work, w
entropy, S
heat, q
temperature, T
enthalpy, H
free energy, G
reaction quotient, Q
equilibrium constant, K
…we discover the basis of reaction quotients
and consider system and surroundings…
internal energy, U
work, w
heat, q
surroundings
entropy, S
system
temperature, T
enthalpy, H
free energy, G
reaction quotient, Q
equilibrium constant, K
…enthalpy is seen as a measure of the entropy
change of the surroundings…
internal energy, U
work, w
heat, q
surroundings
entropy, S
system
temperature, T
enthalpy, H
free energy, G
reaction quotient, Q
equilibrium constant, K
…now we are ready for free energy…
internal energy, U
work, w
entropy, S
heat, q
temperature, T
enthalpy, H
free energy, G
reaction quotient, Q
equilibrium constant, K
…and we can see how free energy ties it all
together…
internal energy, U
work, w
entropy, S
heat, q
temperature, T
enthalpy, H
free energy, G
reaction quotient, Q
equilibrium constant, K
…lots of fun demos and applications…
internal energy, U
work, w
entropy, S
heat, q
temperature, T
enthalpy, H
free energy, G
reaction quotient, Q
equilibrium constant, K
…later, we come back for a brief discussion of
free energy in relation to electrochemistry.
internal energy, U
work, w
entropy, S
heat, q
temperature, T
enthalpy, H
free energy, G
reaction quotient, Q
equilibrium constant, K
…for about 8 weeks we study thermo…
…now for what the students say…
Thermodynamics
Electrochemistry
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/hansonr
BCCE 18, July 19, 2004