4. Physical Chemistry: The rise of thermodynamics

It may seem easy (specially in hindsight) to find common ground between chemistry and physics. But not so in the late 1800's when that terrain was barely tread. First, you must determine which physics to use, and how it might have something, anything, to say about the chemistry of your system. This is where thermodynamics comes in. It was a relatively new physics at the time. Gibbs gave it root; Ostwald and van't Hoff used it to make physical chemistry a science.  The success of thermodynamics lies in its ability to describe energy transactions between large bodies. These bodies can consist of a single type of atom or molecule like a pure glass of water or, more likely, it can be a mixture. No question that mixing liquids is fun, but the action lies in having them react. The use of thermodynamics to describe chemical reactions gave rise to what may have been the first significant interdisciplinary application of physics to chemistry. Thus the field of physical chemistry was born.

The power of thermodynamics to describe chemical processes—like reactions and phase transitions—is so great that it still fills much of the material that we teach in general chemistry courses. It's useful to understand that atoms and molecules exist as indivisible objects—up to chemical bonds—which allows us to create balanced reactions that also reflect energy transactions. So what need does a chemist have for any other physics? Sadly, the American Chemical Society (ACS) Journal of Physical Chemistry (founded in 1896) and their editor—Wilder Bancroft—answered this question in the negative well beyond the 1920's. Lest you think that Bancroft was a heretic, it is important to note that he was a graduate student of Ostwald and a postdoc of van't Hoff! Under Bancroft's rule, the Journal defined physical chemistry as only that science which involved the use of thermodynamics to understand chemistry. Pretty powerful, yes, but also limited.


(This is the fourth post in a series starting with the first one on interdisciplinary sciences.
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3. Physical chemists are who physical chemists train (and a few others too!)

If we are going to ask about the ontology of physical chemistry or chemical physics, it is perhaps useful to start by asking who adopts these titular phrases in the first place. The funny thing is that a scientist's self-identity is typically directed according to the so-called academic genealogy that follows the mentor-apprentice relationships  conferring doctoral degrees. Though not as formally granted, postdoctoral training is also included in academic genealogies, thereby conferring multiple "parents" to a single scientist. Not surprisingly, there are websites such as http://academictree.org that track these lineages. An early such project started at Illinois catalogs the academic genealogies of their faculty (http://www.scs.illinois.edu/~mainzv/Web_Genealogy/) and a few other notable chemistry departments. An interesting book by Paul Servos tracked the history of physical chemistry according to the line of chemists starting with Friedrich Ostwald through to Linus Pauling...

Linus Pauling (1901-1994)

Cal Tech, 1925

NOBEL PRIZE (CHEM), 1954

NOBEL PRIZE (PEACE), 1962

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Roscoe Gilvey Dickinson (1894-1945)

Cal Tech, 1920

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Arthur Amos Noyes (1866-1936)

Leipzig, 1890

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Friedrich Wilhelm Ostwald (1853-1932)

Dorpat (Latvia), 1878

NOBEL PRIZE (CHEM), 1909

The funny thing is that the academic genealogy of most (American) physical chemists overlap with at least one of these nodes (either through the graduate student or postdoc lines). Mine is no exception as you can see from my academic genealogy (at http://www.chemistry.gatech.edu/rig/cgen.html) which meets the lineage at Pauling. One notable exception is Ira Remsen who was among the first of the American Professors to train and sponsor Ph.D.s in this country (at the Johns Hopkins University). I don't know the extent to which the academic genealogies of physical chemists around the world also trace back to Ostwald. I would be happy to hear if yours does or does not!

The point of all of this is that physical chemistry as a field has been critically shaped by the intellectual movements from Ostwald's school. It's not an exclusive club, however, nor should it prevent such physical chemists from expanding beyond. Indeed, what has made physical chemistry an exciting field is the ever changing paradigm shifts that have advanced our fundamental understanding of the chemistry and physics of atoms and molecules. This requires diversity of thought. It has evidently come from the subsequent generations despite our tight academic lineages.

(This is the third post in a series starting with the first one on interdisciplinary sciences.
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2. What's in a name? At the crossroads between chemistry and physics

In the 1700's, a dramatic paradigm shift was brewing in the chemical sciences. Until then, chemistry had been part art and part taxonomy. The question was whether one could make sense of it all based on fundamental principles about the substances themselves. (We didn't quite yet know that substances were made of tiny building blocks, namely atoms.) Or to put it bluntly, is there an underlying physics to chemistry? Thus physical chemistry (or is it chemical physics?) was born as an interdisciplinary science. It's now a part of the core of the discipline of chemistry. It is also a popular node in the web science in which the interdisciplinary sciences act as the links.

The interdisciplinary field lying between chemistry and physics took hold in the late 19th century. Ostwald recognized the power of the new physics of the day—thermodynamics—to help make sense of the energetics or molecular motions and reactions. Thus was born the field of physical chemistry, and the eponymous journal within the American Chemical Society. The trouble is that when new physics—such as quantum mechanics—came along, the editor of the Journal of Physical Chemistry at the time wasn't ready to accept it. This led to the rather odd definition of physical chemistry as being limited to the thermodynamics of chemical processes. This, in turn, necessitated the definition of a new interdisciplinary field, chemical physics, which included the use of all physics (even thermodynamics) to understand chemical processes. As the corresponding eponymous journal was subsumed under the umbrella of the American Institute of Physics, some chemists (though not most) did not make the jump to chemical physics. This, in turn, led the Journal of Physical Chemistry to focus on topics in the middle of the 20th century with decreasing relevance. (Fortunately this misdirection did not persist, and the happy ending is coming soon!) Meanwhile, the name confusion continues to recur as students routinely ask me what exactly is the difference between chemical physics and physical chemistry today. My answer to the question follows in the posts to come!

(Note that this is the second post in a series. Click here for the previous post.)