Thermodynamic Puzzle
To the Editor: The statement is generally made' that the Principle of Microscopic Reversibility (or Detailed Balancing) cannot be derived from thermodynamics. It seems, however, that a perpetual motion machine of the first kind (one that violates the First Law of Thermodynamics) could be constructed if the Principle were not true. If so, this would constitute a thermodynamic proof of the Principle. Consider the system R (reactant) = 2P (product) where R and P are gases. Assume that there are two sets of paths for reaction, one a catalytic path and one not. With both paths operable, i.e., catalyst in system, the system would be a t an equilibrium state EQ. Now remove the catalyst. If the Principle did NOT hold, the system would shift to an equilibrium state EQ*. Replace the catalyst, and the system shifts back to EQ. If the system is in a cylinder with piston, these shifts could be made to do limitless external work. (The above argument is essentially that used by van't Hoff for his "catalyst box.") In the diagrams below, the numbers of molecules moving along the various paths in unit time are represented by a and b. Diagram A shows the situation if Microscopic Reversibility holds, while B shows the case if it did not hold.
i.e., the same order of magnitude. This result offers a striking example of thermodynamic unity in the world. GIORQIONEBBU
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C. M. DELANEY
z D ~ ~ l AND ~ L 5 ALBERTY. "Phvsicd Chemiatrv." ". DENBIG!?. "The Principles of C h e d c d ~quilihrium," and BOUD& Kinetics of Chemical Processes!'
Volkswagen versus the Hummingbird
To the Editor: I have just read the interesting note by E. R. Gerlach in the July issue of THIS JOURNAL (p. 455). Although the reasoning is fully correct, the numerical values and the conclusions are not. Assuming a low heat of combustion value of 12,000 kcal/kg for gasoline and of 9,000 kcal/kg for animal fat, one obtains the following figures Efficiency Hummingbird
11'900 = 995 (miles)(g)/kcal 12
Volkswagen
7'680 9
UNIVERSITY OF B m BAR',ITALY
Undergraduate Organic Chemistry
To the Editor: I n reference to Robert B. Smith's paper [J. CHEM. EDUC.,46, 273 (1969) 1, I have had some experience in graduate school a t Kansas State University with this excellent method of teaching organic chemistry to undergraduates. It is very encouraging to see more instances of the dynamic approach being applied to the acquainting of students to organic chemistry. I hope to see this method being used in a11 universities of this country. The concept of letting the student think for himself pays off in terms of a more alert student and more of a welcome challenge to the teacher and the graduate student teaching assistant. The student reaction which I experienced was similar to that described by Smith. There was an enthusiasm exhibited by the students that was thoroughly enjoyable to see.
A TMS Sampling Technique
To the Editor: A note has recently appeared concerning the handling of low-boiling liquids [(J. CHEM.EDUC.,46, 289 (1969)l. We wish to bring to the attention of your readers an alternate simple technique for the transfer of tetramethylsilane into nmr sample tubes. Since TMS is generally obtained in a septum-capped vial, or may be placed into a container of this type, we found it useful to cut a needle off at its base, bend it 90' near the center, and puncture the cap. The needle is brought just above the level of the TMS while the other end may be held a t the top of an nmr tube. By tipping the vial slightly one end of the needle goes down into the nmr tube and the other comes into contact with the liquid. Its volatility alone is sufficient to maintain a rapid flow which is terminated simply by turning the vial upright. The needle may then be removed and reinserted for later use. DONALD F. MONTECALVO JOSEPH F. LAWLOR
860 (miles)(g)/kosl
Volume 46, Number 10, October
1969
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