What Thermodynamics Should be Taught to Freshmen, or What is the Goal? Pretude: These comments concentrate primarily on the educational goals for that great majority of students who take college chemistry, hut are not going to he scientists, and secondarily on those who will not use thermodynamics professionally. The tiny fraction who will use thermo explicitly will have plenty of exposure later, hut they would still gain insight by appropriate early treatments. The great majority of students in current first-year college courses must try to work problems involving changes in enthalpy, entropy, and Gihhs Free Energy. Practically all students must deal with endothermicity and exothermicity and have had to do this for a long time. Perhaps a current TV fmw fir(, protcvnnn slogan ii suifirient just~fication.It slates 'Only. .vnu ran prevent euothermic reactions." And then, of course, there is C. P. Snow, "-I-have asked company how many of them could describe the Second Law of Thermodynamics. 'I'he response wasruld; it wns also negative. Yet 1 was ofankiny somcthiny which is ahout tht: srirntiticl.((~~ivnl~nt Have vou read 3 work of Shakesoeare?" I1 . .I. Snow's comoarison may not he the reason (he later even regretted choosing that examole). . . hut entronv ."is referred to more and more in journals of opinion, in the public press, even by professional comedians such as Flanders and Swann in their insightful "Laws of Thermodynamics," which ends with "- hat's entropy man." And some of our more perceptive analysts have correctly noted that the world is not faced withan energycrisis (energy is conserved), hut with an entropy crisis (a high and namics" than tradition, culture, and ihility to read newspapers and listen to TV. Can chemists even areue that this erowinc inclusion of thrrm(alyn;~m~c rwms in thr gt:neml vocahulilry justifies, or is i.,srerrd h\,. our intrnductor\f trearments? It would he hard to argue so the light of most current presentations. But exceptions exist. Each year a few more chemists discover that c s not rlwtml~lerigor mortis. thr rigur of t h ( r m ~ d v n a m ~ntvd 'I'hev learn that hrat engines area great a a v toleavestude~~ts coldand, in fact, that heat engines are better omitted from introductions. More successful is a direct approach correlating all ohservations with the "natural tendency" of strong hoods to form and of disorder, or spreading out, to increase. This makes "sense," even if enthalpy and entropy are never mentioned. Both students and teachers find the concreteness of the readilv observed tendencv of mass andlor enerev -.to soread . out in every total change ankasier concept to accept and use than the formal idea of conservation of energy. And all this without recourse to calculus, or any other mathematics more complicated than addition, subtraction, multiplication, and division. The ideas can even he treated successfnlly with no arithmetic, only observation. Some of us suggest that the difficulty (and real it is) with the use of thermodynamic ideas in chemistry (at all levels) is not in the "formality" of the ideas themselves, but in the formality of the presentation. For example, most students learn (or are told) early that "energy is conserved."Quite often (Continued on page 521, column I )
in
520 / Journal of Chemical Education
Why lhermodynamics Should Not be Taught to Freshmen or Who Owns the Problem? Thermodynamics should not he taught to freshmen-there are better things to do with the time. I say this despite the plethora of well-meaning and frequently ingenious ways that have heen promulgated to explain thermodynamics and make it easier to learn. Let me digress here to make a few comments about the nature of college level teachers. We were probably the brighter students in our classes, adept a t mathematics and formal logical thinking. Explanations appealed to us and worked to satisfy our curiosity. We currently have great knowledge and experience in chemistry, as contrasted with our students. But, alas, our students are not us. In addition, there is most likely a difference in eenerations between us and those we teach. \i'hat makes iense and appeul.; I,, us mny 111. irrrlwnnt a r incom~rehmsihlr them. This is n hv I ask t hr c~urutiun'\\'hu owns the problem?" Those of you who are familiar with transactional analysis and, in particular, with parent effectiveness training will recognize the question. In matters of conflict between parent and child it is important to know to whom the problem is important. Do you or your child care more about how helshe keeps hislher room tidy? There is a parallel here for the interactional pair of teacher and student. For whom is it more important to provide theoretical, basic, fundamental explanations to all the phenomena which are now crammed into general chemistry? Are our students really clamoring to know all about quantum theory so they can end their confusion about whv it is RhCl and not RhCL that one eets from Rb(s) c l z ( g ) f ( l nmy day something c&ed "val&ce" which was memorized seemed to he sufficient and, what is more, worked!) 1)o m ~ students r wait u,ith haired hreath tt, h w e the law o i mass artion r x ~ ~ l n i n hs r d rhr reaction isuthernm'?'I'he\, . nppedr .. to have enough trouble-doing practical equilibrium calculations without the addition of a fundamental explanation for what it is they cannot manipulate. Who owns this prohlem? \Ve du. \Ve do s h e n u,c make choices that satisfy-our needs for theory and explanation and order in the presentation of material. To the sophisticated chemist i t makes sense to go from the atomic and molecular level to that of observable macroscopic phenomena. One explains the other, doesn't it? Or, could it he just as sensible to explain chemistry using "combining powers" and "valence?" Group I and Group VII elements form one-to-one compounds with each other regardless of whether students know about s and p orbitals. Equilibrium constants and Le Chatelier's principle work whether we invoke the Gihhs function. Hess' Law is quantitative and can he used whether students know about state functions and enthalpy changes a t constant pressure. I do not think that the parallel between parents and children on one hand and teachers and students on the other is inappropriate. As a parent I struggle with giving advice (explanations) and not getting in the way of my boys learning for themselves by themselves. I know how hard it is to hold (Continued o n p. 522. column I )
+
What Thermo Should be Taught.
..
Conserves enem
System
this is followed by "exothermic reactions generate energy," and "endothermic reactions use up energy." Seldom is the conservation idea then used to show that every exothermic process is accompanied by an endothermic one, and every endothermic nrocess hv an exothermic one. Often the impression is given that exothermic processes are common, eudothermic uncommon, whereas actually hoth always occur together and there are the same number (exactly) of each as described hv conservation of enerw. The reci~rocitvis easv to demonstiate by using a warming finger todeteci the endothermic change accompanying an exothermic change, or vice versa. Here is concrete learning in the best Piaget manner, rather than the formal style found difficult by many first year (and later) students. Concrete and formal become confused aeain in the nresumed separation of types of chemical reactions into reverkble and irreversible.. auicklv followed bv the introduction of . equilihrium constants where all reactions are treated (correctlv) as reversihle. We can't have it both wavs in exoerimental (concrete) terms, but insist on hoth usages in fdrmal (and here incorrect) treatments. Adherence to thermodynamic arguments would both simplify the treatment and enhance the com~rehension.Students would then see that all net changes in closed systems are reversible, and all net changes in isolated systems are irreversible. The criterion is the nature of the system, not the extent of the change. Were this criterion understood widely, humans would make much more sense in discussine environmental and ecoloeical a maior " ~roblems. . goal in much of contemporary education. It is when we concentrate on humans and forcet - their surroundinm - that manv major blunders occur. Much of the reluctance to use thermodynamics, especially entropy, comes from the exotic nature of the names, and Greek stems at that. So I suggest, as a first change, that early use avoid the Greek stems. The likely gain in comprehension will almost surely offset the certain loss in precision. But precision is more apt to follow comprehension than the reverse. We need neither the classical nor the statistical approach, hut an atomistic and molecular one which ties in with the general emphasis that chemists are people who interpret hulk ohservations in terms of molecular behaviors. As to content and sequence, let me immodestly suggest reference (21, especially Chapter 20. Most readers have a copy, any short outline here would be inadequate and misleading, while half-an-hour spent there would provide examples of a possible development, a set of non-numerical exercises, and opportunities for a more thoughtful perusal if the sampling suggests it. A narrow scientific goal of a thermodynamic development is to show that iust as atoms of an individual element can he assigned sizes, A d just as honds between pairs of elements can he assigned strengths, so (but much more accurately) reactivities of individual elements and compounds can he assigned numbers. These numbers can he mani~ulatedto oredict direction of chemical change and to give equilibrium data. But a much broader goal is to enlarge the application of these ideas to changes in general. A student who understands the inevitability of increasing entropy, but the possibility of local decreases, may well waste less time in futile attempts to "violate" the second law and so reap the reward of a more satisfactory life. After all, we live in a system which must always he considered in relation to its surroundings and the interactions between the two. Let me emphasize that many of the most important and useful ideas from thermo can he developed without using the
' Snow, C. P., "The Two Cultures," Cambridge University Press, 1959.
Campbell. J. A., "Chemistry, the Unending Frontier," Gwdyear, 1978.
Crlterla tor Equlllbrla In Varlous Types of Systems
Table 1.
Direction of chanw
Criterion at equilibrium
mass isolated yes closed yes open no
Table 2.
yes
no no
-
-
-
-
+
+
-
.-
-
AS=o A G = o , A H = TAS
no equilibrium possible
-
Change In a System of Constant Mass, Pressure, and Temperature
r----Algebraic
AH
AS> 0 AG
