While teaching remotely during the pandemic, I tried to mix things up in my classes. Thus, on May 4, I did a Star Wars day lecture in my G-Chem class. It was an excuse to talk about several things: (1) that living systems try to stay away from thermodynamic equilibrium, (2) my research into the chemistry of the origin of life, (3) the search for life on Mars, and (4) how E.T. might phone home via the hydrogen 21-cm line. That’s an eclectic mix of topics.
I’ve kept up the tradition in my G-Chem II class the last several years, making small changes every year. I did so again yesterday, the Friday just before Star Wars Day. I think it was well-received and students participated in answering my questions which I had pitched as reviewing the topics for the semester. I now introduce the class as a connection between equilibrium thermodynamics (which takes up most of the semester) and the last few classes that cover electrochemistry and redox reactions.
We begin with a reminder of isolated, closed, and open thermodynamic systems. We talk about equilibrium being thermodynamic death: when there’s no longer any Gibbs free energy to access, organisms can’t extract chemical energy to do work! Then we talk about the oxidation of sugars into CO2 and H2O as a placard for catabolism. Students remind each other what enthalpy and entropy signify in a chemical reaction. When I ask them where the sugars come from, we then discuss the reverse reductive reaction: photosynthesis. Students dredge from their memory how to determine oxidation numbers of carbon so they can identify the redox reactions.
I then ask them why anabolism might take place if the reaction of CO2 and H2O to form glucose and O2 is so thermodynamically unfavorable? That gets us into discussing photons as “low entropy” concentrated packets of energy, as in contrast to dispersed heat that cannot be recovered. Then I segue to how on early Mars (or Earth), CO2 might react with H2 (both exergonic and endergonic) to synthesize formaldehyde. This allows me to introduce the formose reaction and autocatalysis. We compare the pitiful energy extraction from anaerobic metabolism versus aerobic metabolism. I show them graphs depicting the rise of O2 on Earth and the evolution of manganese-catalysts in photosystem II. Finally, we get to humans burning hydrocarbons for even more energy!
Communicating with alien life now takes up only a small portion of class time. We discuss the dominance of hydrogen in elemental abundance. Students are reminded of the emission spectra and electronic transitions. I remind them of electron spin and introduce the 21-cm wavelength associated with that transition. We discuss how an Earth scientist might communicate with an alien scientist by trying to find unitless quantities such as pi or the fine-structure constant embedded in the hydrogen spectrum.
Then I tell them about the movie “Contact”. It’s old and none of them have watched it (although I encourage them). I then tell them about the SETI message beamed out from the Arecibo telescope. I also show them pictures of the now destroyed telescope and tell them it’s not because James Bond had to foil a terrorist incident (GoldenEye). We briefly talk about why you might not want to communicate with aliens, and I mentioned The Three Body Problem. (One of my students had watched the first season. I haven’t yet.) I end with the Chibolton “reply” crop-circle which is always jaw-dropping because students have never heard of it; I suppose it’s good that none of them are into weird alien conspiracy theories, or at least no one has admitted it yet.
Another Star Wars day come and gone. I had fun! Hopefully the students enjoyed it too. On Monday we dive into redox and electrochemistry.
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