A
SYMPOSIUM
The Teaching of Thermodynamtcs Introduction This symposium, held a t the Washington meeting of the American Chemical Society in 1962, arose from the conviction of many chemists that a fresh look a t thermodynamics in the chemistry curriculum is desirable. Such re-examination is warranted among other reasons because curricula and courses are changing rapidly a t all levels from the high schools to the graduate schools. The speakers a t the symposium shared a common active interest in the teaching of thermodynamics but they differed in focus. Altogether they covered the range from the freshman year to the formal senior or graduate work in their comments. Professor I. Oppenheim discussed an advanced course in thermodynamics and showed how the fundamentals of thermodynamics can be applied rigorously and logically to chemical systems in terms of measurable quantities (rather than in a too extensive use of molecular, statistical thermodynamic considerations) to yield useful results. He illustrated the operational approach in his applications to molecular weights and to gas mixtures. The other speakers, whose papers follow in this report, showed how thermodynamics can aid in an understanding of chemical problems in the freshman and sophomore years as well as in later courses. Thermodynamics, a relatively old science, has been making a steadily increasing impact on chemistry. It first entered the chemistry curriculum as a senior or graduate course, but it has since descended into the physical chemistry course and become a substantial part of it. Today many chemists believe that the concepts of thermodynamics are too useful to be deferred until the junior or senior years-by then most students are already confirmed in earlier, empirical ways of look'mg a t chemical problems. AU teachers in the undergraduate courses in general, analytical, and organic chemistry "have had" thermodynamics, but most of them refrain from applying it in their courses. Hence, the students meet important concepts of thermodynamics for the first time in their physical chemistry course. Typically, the first law is expressed in verbal form a t the beginning of the general chemistry course and is thereafter neglected except by those teachers who discuss the energy change in chemical reactions in some detail. Or sometimes the enthalpy function, expressed as AH, may be used to represent heats of reaction. I n some courses, the freeenergy function, 4F or AG, is correlated with net reversible work or with the chemical equilibrium constant. Then tables of oxidation-reduction half reactions may show decreasing values of the standard free energy 490 / Jotirnal o f Chemical Education
change (in calories) rather than increasing values for the standard half-reaction potential (in volts). To he sure, the second law is involved implicitly in the free energy function but the interdependence is usually not mentioned. Rarely does the concept of entropy or the term itself appear. A recent study1 of the opinion of college teachers on a desirable course content in general chemistry placed entropy as next to last and thermodynamics fourth from last in a list of 230 items or topics. Yet, Hess' law, a special case of the first law, was in the third quarter of the ranking. There is little evidence that thermodynamics is more widely applied in elementary analytical and organic chemistry courses than in general chemistry. One of the perennial difficulties of beginning chemistry students is understanding the reversibility of chemical reactions and the concept of chemical equilibrium. Energy considerations alone are not enough to explain reversibility and equilibrium, for reaction products can exist even though they have more energy than the reactants. MacWood and Verhoek2 have discussed this point in a paper on "How Can You Tell Whether a Reaction Will Occur?" They showed, in terms intelligible to a freshman, how a tendency toward greatest randomness or highest entropy can counteract a tendency toward lowest energy. Editorial comment3 in THIS JOURNAL has also argued for an early introduction of entropy into chemistry courses. At moderate temperatures there is little that we can do to alter the value of 4E or AH for a chemical reaction -the values do not change rapidly with temperature or with concentration. On the other hand, we can and often do alter the values of A S and TAS by solution or dilution (or concentration) processes. Whenever we manipulate concentrations we change entropies. Much of chemistry is concerned with the manipulation of experimental conditions to produce desired materials. Perhaps, in explaining reversibility and chemical equilibrium we should be emphasizing the battle for supremacy between TAS effects and 4E or AH effects. The free energy change records the result of the battle but the term "free energy" itself does not help the student understand what is happening. Undoubtedly, the mathematical facility required for a rigorous study of thermodynamics has deterred many teachers from applying thermodynamics to the earlier chemistry courses. However, students are now entering NECHAMKIN, H., J. CHEM.EDUC.,38, 255(1961). 2 M ~ ~ W o G. o ~E., AND VERAOEK,F. H., J. CAEM.EDUC. 38,334(1961). "Editorially Speaking," J . CAEM.EDUC.,38, 333(1061).
college with better mathematical facility; we may expect further gains as the cumulative effects of the newer mathematical programs in the elementary and high schools appear. Even now many college students become ready for simple applications of the calculus during their freshman year. For them this difficulty is vanishing. I n any case, much can be done to avoid use of the calculu~,~ even though some precision and generality is sacrificed. We do not avoid using the term velocity, for example, until after students have had calculus. Similarly, PdV work can be understood quantitatively for a system a t constant pressure and See, for example, HOWALD, R. A,, J. (1958).
&EM.
Ennc., 35, 293
qualitatively for more general conditions. One may argue further that a chemistry student of systematic thermodynamics will understand it better if he has learned to think of energy, entropy, and work in concrete physical terms. Then the operations of the calculus will be more meaningful. Each reader of the symposium papers will weigh them in the light of his own experience and inclination. He is reminded, however, that the papers are based on actual classroom experiences which show that a t least some parts of thermodynamics may be learned in the first years of the chemistry curriculum. 1. E. Steiner, Symposium Chairman Oberlin College, Oberlin, Ohio
Volume 39, Number 10, October 1962/
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