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Wednesday, July 7, 2010

Of Thermodynamics, Chemistry, Biology and Biochemistry ~ Feinman Reply

In response to, this post:

Fred Hahn said...

I am posting this comment on behalf of Dr. Richard Feinman, professor of cellular biology at SUNY Downstate. 
"I never had to go through steam tables but I still teach bioenergetics in biochemistry courses where we think thermodynamics has a lot to do with human metabolism. 
Like most chemists and even some physicists, I would be willing to admit I don't understand the field that well but if you have a problem, feel free to write to me directly. 
I think it is touching that people get excited about thermodynamics but I expect polite discourse. 
Richard Feinman 
Professor of Cell Biology 
SUNY Downstate Medical Center 
feinman@mac.com


Here's the discussion at Eades' blog that resulted in my steam table comment:

Jim B, March 6, 2010 at 9:41 pm
In the last year, or so, I have experienced a re-education on thermodynamics. In the last 20 years or so, there has been a mojor change in the way the subject has been taught.
For over a century, the field was taught with primary emphasis on the heat engine, and a rigorous and nearly total exclusion of modern physics concepts – in particular quantum mechanics.
By introducing quantum concepts of “states” of a system, and the ability of people to “count” or enumerate the possible states of a system, the whole field can be made easier to understand.
Under the old system, it was often easiest to rely on memorization and pushing equations around to survive and answer test questions — but still to not UNDERSTAND what is going on.
The new system is much more rational. Less memorization is called for.
IRREVERSIBILITY
If you drop a book onto a table, all of the potential energy of the book is converted into heat in the table (and to pressure waves of the sound which ultimately end up as heat). The conversion of potential energy to heat is essentially perfect.
Yet, the heat in the table and the sound waves in the air never come back focused in time and space to recreate the conditions that existed on the falling book impact and then propel the book back into the air.
However, it is possible to convert electricity into potential energy at nearly perfect efficiency with a friction free electric motor(with superconducting wires) and a pulley and weight. It is possible to take the same weight and pulley and an electric generator (frictionless and superconductive wires) and nearly perfectly convert potential energy into electrical energy.
Heat – is impossible to convert perfectly into any other form of energy.
Heat = Thermal
Thermodynamics = dynamics of heat. conversions…. as the origin of the word.
The study of the strange way heat stubbornly resists efficient conversions to work or other forms of energy.
[ ... snip]

Reply
mreades, March 7, 2010 at 12:42 pm
Maybe I should go back and give it another look. I still get hives when I think about the steam table problems I had to do in my thermodynamics course in engineering school.
Reply
Richard Feinman, March 7, 2010 at 12:54 pm
Jim B,
What are the sites on the internet you had in mind? I did not find my thermodynamics courses so bad as difficult to understand (although I may still not know enough to distinguish). The reason that the subject is so elusive is that it is not a molecular science which is what we are good at. Rather it is physics of aggregates, that is, ensemble properties which we don’t have good intuitions about. Arnold Sommerfeld put it well.
He was one of the great physicists in the development of quantum mechanics but was considered an expert on most areas of physics. His take on thermodynamics along the lines of your description:
The first time I studied it, I thought I understood it except for a few minor details.
The second time I studied it, I thought I didn’t understood it except for a few minor details.
The third time I studied it, I knew I didn’t understood it but it didn’t matter because I already knew how to use it.

I've got to say it is sad that someone of Dr. Feinman's education could participate in this thread without demonstrating a MASTERY of chemical thermodynamics (no steam tables need apply) since he teaches a related topic.  I've studied thermo at both the undergraduate and graduate levels in physics, physical chemistry, biochemistry (and moreso in the offering from the chem dept vs. bio dept), electrochemistry, diffusion, advanced chemical kinetics, and metallurgical thermo.

So I'm "touched" that Dr. Feinman responded indirectly, but not by his condescending reply.  And I'm troubled that he doesn't seem to be versed enough in chemical thermodynamics to at least interject into that discussion that steam engine thermo is totally irrelevant to biochemistry.  I would also have to differ a bit with the first commenter quoted, Jim B.  There's no "old way" vs. "new way" to learn thermo -- it's just that it is different in different contexts. Likely, the first time most scientists and engineers encounter thermo is in a physical science class hence steam engine.  In that context we don't even associate entropy with "randomness", we deal more with the concept that heat cannot be completely converted to other forms of energy.

Entropy is a rather simple concept in Chemistry.  Although it may be difficult to understand how it is determined, the spontaneous "urge" towards a disordered state is a concept easily digested.  Free energy calculations are straight forward -- no calculus involved either.

There's also a trend in posts of people equating/confusing heat production with entropy.  This is in error.  Heat is an "out" term in the energy balance equation for a human being.  Even if we are put in a hot room, our bodies actively try to keep our body at appropriate temp ... we don't try to convert heat to other energy forms.  Heat is enthalpy, not entropy.  Indeed all of the enthalpy "H" terms are all called "heat of ____"  formation, solution, etc.  Just because heat is required (endothermic) or released (exothermic) in a chemical reaction this does not necessarily correlate with entropy changes.

I think the reason Atwater's calorie values tend to hold up pretty well is that they were determined for humans.  I have no doubt that any single individual might be able to eat a few more or have to eat a few less calories on extreme macronutrient restricted plans as they may well possess a genetic/biologic makeup that processes one or the other more efficiently, but genetic defects in these processes are rare.  But it seems highly unlikely that differences in efficiencies and entropy losses for energy production in humans are considerably different for the macronutrients.  I say this because the bulk of the production of our major "fuel", ATP, is generated in the SAME "engine" -- Krebs & ETC.

I will do a follow-up post in response to this because I've wanted to address the 2nd Law paper (What is someone who admits not understanding a field doing writing a paper on it anyway?) and Feinman's comments in that Eades blog post for a while now.

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