Chemical Education Today
Letters Chemical Thermodynamics in the Real World One of the world’s greatest challenges, at present, is to find a formula for fighting terrorism, while preserving civil liberties. The March 2005 anti-terrorism conference in Madrid is but one example of officials and experts seeking to address the same paradox. Some 34 years ago, one part of a Priestly Medal Address by F. D. Rossini from the University of Notre Dame discussed an interesting application of thermodynamics to this paradox. Below are excerpts from the address. In light of the everincreasing need for compromise, Rossini’s observation now seems all the more relevant. (Reprinted with permission from Chem. Eng. News, April 5, 1971, 49 (14), pp 50–53. Published 1971 by the American Chemical Society.) With the first and second laws of thermodynamics we can derive two important equations:
∆G ° = −RT ln K ∆G ° = ∆H ° − T ∆S ° Since the term on the left side is the same in the two equations, the quantities on the right side are equal to one another. Hence we can write or
−RT ln K = ∆H ° − T ∆S ° ln K = −
∆H ° 1 R T
+
∆S ° R
From this equation, K increases with increase in ∆S°; and K increases with decrease in ∆H°. Increase in ∆S° comes with increase in randomness, leading to greater “freedom” in the system. Decrease in ∆H° comes with increase in the energy of binding of the atoms in the molecular structure, leading to greater “security” in the system. These are opposing factors in the evaluation of K, and hence, for a given temperature, the final state of equilibrium is a compromise between the “freedom” term, ∆S °兾R, and the “security” term, ᎑∆H°兾RT. Here we have an interesting picture derived from our science of thermodynamics—equilibrium or stability is a compromise between freedom and security. In terms of human experience, the meaning of security can be interpreted to mean that one is secure and safe in his person, in his family, in his home, in control of his property, on the streets, and on his travels. The meaning of freedom is quite clear—the privilege of doing whatever one wants to do. However, in our civilized society, we have come to believe in behavior according to natural law—that one can do whatever he wishes so long as he does not abridge or infringe upon the rights and privileges of others. To me, all this means living with some rational kind of law and order. The picture we have developed from thermodynamics is very simple: One cannot have a maximum of freedom and a maximum of security at the same time. If there is a maximum of freedom, there will be zero security. I interpret this to mean that if we have total freedom, everyone can do whatever he wishes, including injuring others, stealing property, and the like. On the other hand, if there is a maximum of security, there will be zero freedom. I take this to mean that
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if we have total security, we will be constrained at every step and have a virtual straitjacket life. One sees that there is a trade-off between freedom and security. In a state of total freedom, we can afford to give up some freedom to obtain some security. The ideal situation would appear to be one in which we have established that amount of security necessary to have human beings live happily and in harmony with one another, through observance of an appropriate amount of law and order, and then to have as large an amount of freedom as can be accommodated in this situation. Harold E. Leonard 3441A E Lake Road Skaneateles, NY 13152-9000
A Response to Chemical Thermodynamics in the Real World By making available an excerpt from Rossini’s address, Harold Leonard has given us a good example of anthropomorphism in chemistry. The concepts of “freedom” and “security” (like “order” and “randomness”) were parts of our cultural heritage long before modern thermodynamics was formulated. Entropy was defined solely in response to the need to explain certain modern experimental observations. It was never necessary to invoke concepts like “freedom” and “security” to systematize these same specialized experiments. At best, associating “freedom” with entropy is similar on other loose associations as when we say a shaft moving in an oversize bearing has too much “freedom”. While there is a “freedom” for which one might die to defend, it is certainly not the “freedom” of an oversize bearing nor that of entropy. Such anthropomorphic associations might help some students absorb abstract concepts. They certainly are not part of the conceptual framework of the science. The danger of such anthropomorphisms is that we really come to believe that there is substance in them. In this particular case, there is the danger that true human freedom will be reduced to some sort of physical freedom on the same par with entropy. There is the danger that some will think that true human freedom can be measured in terms of some sort of calculus of simultaneous maximums and minimums. And worst of all, there is the danger that chemical thermodynamics will have ascribed to it a power that it simply does not have, namely, the power to “explain” the human condition. There may be a sense in which Chemistry is the “Central Science”. This is certainly not it. It is possible that Rossini did not intend his associations to be taken as seriously as suggested here. Nonetheless, rather than encourage loose thinking through the use of such anthropomorphisms, it would be wise to purge them from science. Let Chemistry solve those problems for which it was created. Let true Wisdom solve the problems arising from the human condition. John F. Wójcik Department of Chemistry, Villanova University Villanova, PA 19085-1699
[email protected] Vol. 83 No. 1 January 2006
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Journal of Chemical Education
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