Saturday, December 4, 2010

Simulations in teaching physical chemistry: thermodynamics and statistical mechanics

In this post I summarize the simulations and I have used in teaching thermo and stat mech, and talk a bit about how I use them.

I co-teach two quite similar courses on this topic: one for nano-students and another for chemistry and biochemistry students.  In the nano course we use the book Molecular Driving Forces by Dill and Bromberg, and in the other Quanta, Matter, and Change by Atkins, de Paula, and Friedman.  At the end of this post I have organized the simulations by chapter for each book.

Some of simulations I have made (or modified extensively) and most of these have been discussed in previous blog posts, so I simply give the link to the respective blog post where there is more information.

The other simulations are from the Molecular Workbench (MW) library of models, and here I provide links that will open in MW, so you need to install MW before clicking on the links.  For some of them I also provide a brief description of what concepts try to demonstrate using the simulations.

How do I use the simulations?
All simulations are used during lecture to visualize concepts, start discussions, and motivate equations. I'll take Illustrating energy states as an example: instead of saying "Molecules in a gas translate, rotate, vibrate, and ....", I say "Here is a zoomed-in view of butane gas where you can see the molecules.  You can see that individual molecules move differently.  How do they move differently?  Anyone?  Right, they have different speeds.  This kind of motion is called translation.  What else? ..."

Practical tips
On a very practical note, my own simulations are all on web sites and I make sure to open all of them before the lecture, while I have all the MW simulations for the course indexed on a single MW page (click here to open in MW). It is not possible to embed these simulations in Powerpoint slides, but you can switch between Powerpoint and other applications without quitting Powerpoint (on a Mac you use command-tab and on Windows i believe it is windowskey-tab).  Note that you need access to the internet in the lecture room.

While I have screencasts of most of simulations on the blog posts, I don't use these during lecture.  I think it is too passive, and puts the students to sleep.  But I believe the screencasts are a good way for the students to review the main points of simulations after the lecture.  I put links to the blog posts on the course web site and in the lecture notes.

Is using simulations a good idea?
If possible I try to use a simulation within the first five minutes of a lecture, and have a maximum of 20 minutes between simulations.  I now only have one (45 minute) lecture left where I don't use a single simulation and I can just feel how I loose the student's attention after about 30 minutes.  You can just see it.  That being said, no one has ever mentioned the simulations in their course evaluations (good or bad), so I have no hard evidence that it improves my teaching.  But I can tell you that I enjoy lecturing much more with the simulations, so unless I get complaints I'll keep doing it. 

Making room for simulations in the lecture
I have taught the topics for many years without any simulations, and was never at a loss for material to cover.  Lecture time is precious, and these simulations take time to present and discuss.  You really have to introduce the simulation carefully (don't rush this part!) before you start them, and very often you want the students to speculate about what will happen before you start them.  Furthermore, they tend to stimulate many more questions, that you can hopefully turn into a discussion instead of simply answering them, than derivations - that's the whole point.

So how do you "make room" for the simulations?  I have cut out most of the derivations from the lectures.  To pay for my sins, I provide relatively detailed (typed) lecture notes ahead of lecture (I generally don't use Powerpoint), which include step-by-step derivations. So I'll say things like "Starting with these assumptions we can write down this equation.  This can be rewritten as this equation, which is much simpler.  The details on how we got from here to there are in your notes, but note that in step 3 we assume that ... which is an approximation."  No complaints so far.  If only more progress had been made on simulating derivations ...

Here are the simulations organized by chapter

Molecular Driving Forces by Dill and Bromberg (1st edition)

Ch 6: Entropy and the Boltzmann distribution law
Illustrating entropy

Ch 10: Boltzmann distribution law
Polymer unfolding: The book uses two simple bead models of polymers in this chapter to illustrate micro and macrostates and model protein melting.  I use this example extensively both in lectures and homework problems.  So I made this simulation to illustrate how higher energy macrostates become more likely at higher temperatures.


Ch 11: Statistical mechanics of simple gasses and solids
Illustrating energy states
Energy states in the water molecule: a slightly more complicated molecule than HCl (used in Illustrating energy states) with more than one vibrational mode and 3 rotational degrees of freedom.
Internal energy and molecular motion
Entropy, volume, and temperature


Ch 12: Temperature, heat capacity
The molecular basis of differential scanning calorimetry: heat capacity and energy fluctuations

Ch 13: Chemical equilibria
Seeing chemical equilibrium (opens in MW)
Dalton's law of partial pressure (opens in MW)


Ch 14: Equilibria between solids, liquids, and gasses
Seeing specific and latent heat (opens in MW): I use this simulation to illustrate how the same substance can be solid, liquid, and gas depending on the temperature.
A gas under a piston (opens in MW): I use this simulation to show that, for example, decreasing the pressure can have the same effect as increasing the temperature.
The phase diagram explorer (opens in MW)
Raoult's law: ideal solutions (opens in MW): Here, I use the simulation of the pure liquid to illustrate vapor pressure.


Ch 15: Solution and Mixtures
Mixing gasses, and mixing of ideal and non-ideal liquids
Raoult's law: ideal solutions (opens in MW)
Raoult's law: negative deviation (opens in MW) 
Raoult's law: positive deviation (opens in MW)


Ch 16: Solvation and transfers of molecules between phases
Visualizing osmotic pressure in an osmotic equilibrium (opens in MW)
Desalination using reverse osmosis (opens in MW)




Quanta, Matter, and Change by Atkins, de Paula and Friedman (1st edition)

Ch 13: The Boltzmann distribution
Illustrating energy states
Energy states in the water molecule: a slightly more complicated molecule than HCl (used in Illustrating energy states) with more than one vibrational mode and 3 rotational degrees of freedom.
Internal energy and molecular motion

Ch 14: The first law of thermodynamics#
The molecular basis of differential scanning calorimetry: heat capacity and energy fluctuations
  
Ch 15: The second law of thermodynamics
Illustrating entropy
Entropy, volume, and temperature
  
Ch 16: Physical equilibria
Seeing specific and latent heat (opens in MW): I use this simulation to illustrate how the same substance can be solid, liquid, and gas depending on the temperature.

A gas under a piston (opens in MW): I use this simulation to show that, for example, decreasing the pressure can have the same effect as increasing the temperature.

The phase diagram explorer (opens in MW)
Raoult's law: ideal solutions (opens in MW): Here, I use the simulation of the pure liquid to illustrate vapor pressure.
Visualizing osmotic pressure in an osmotic equilibrium (opens in MW)
Desalination using reverse osmosis (opens in MW)

Ch 17: Chemical equilibria#
Seeing chemical equilibrium (opens in MW)
Dalton's law of partial pressure (opens in MW)

# I don't teach this part of the course, but if I did I would use these simulations

Related posts:
An Atkins Diet of Molecular Workbench 
One, Two, Three, MD 
Tunneling and STM (a first stab at using Molecular Workbench to teach quantum mechanics)
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