~ornethingnew from the pa/ Teaching Thermodynamics to Beginning Chemistry Students "Entropy a n d Chemical Reactions," J. N. Spencer, David Gordon, H. D. Schreiber. C H E M I S T R Y , 47 1111 12-15,
"A chemical reaction always tends toward formation of stronger bonds and more disorder. These tendencies are measured by the enthalpy and entropy differences between products and reactants. If the tendency far a reaction to occur depends on the resulting bond strengths and disorder, i t is logical t o ask: Which effect determines the direction?" The authors of this article have written an excellent introduction to the concept of entropy. They have written good examples that can serve the teacher in classroom. The articles an this subiect reviewed in orevious columns. Somethine New From the Past (THISJOURNAL.
"Improving Concepts of Energy," Laurence E. Strong, T h e Science T e a c h e r , 35,s-10 (December 1968). There is evidence today that a concern raised by Strong in his article (1968) still persists. "This is the notion that changes occur in a system as a result of a tendency every system has to change t o lower energy . . . There are experimental examples of changes in systems that illustrate all possible energy transactions from energy decrease to no e n w gy change to energy increase. . . Probably the most fundamental statement that can be made about energy is that it is conserved in every transaction that occurs.. . Since energy is conserved, it is not possible for it to be correlated with a change.. Entropy is not conserved and. therefore, can be satisfactorilv correlated with a change." "Spontaneity of Chemical Reaction," H. Dene Weher, CHEM I S N E W S , 8-9 ( M a y 1976). Weber recognizes the need for a teaching strategy ". . .based upon an experimental development of the relationship that exists between spontaneity and the energetics of reactions." He wants beginning students to realize that "(11 soonaneitv is not related to rate of reac-
Edited by: JOSEPH S. SCHMUCKLER Chairman of
Science Education
Temple University 345 Rimer Hall Philadelphia, PA 19122
"Whv Thermodvnamics Should NOT be Taueht to Freshmen or ~ h o ~ o w the n a &ohlem?" These two well known teachers write most understandably. Their arguments are well worth reading. Are their viewpoints really so different? ~~
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"Pollution o n Thermodynamics," William F. Sheehan, CHEM. EDUC., 49 [I] 18, ( J a n u a r y 1972)
J.
One of the most common analogles used in teaching thermodynamics is pollution This reviewer has heard it used several times. . . and the analoev seems t o he useful. Charles E. Hecht. (letter to the editor, 49,6,44;, (June 1972))takes issue with Sheehan's and other's approaches on this topic.
He writes To the Editor: "It is unfortunate that a contribution to the huge pile of articles incorrectly relating thermodynamics to social or philosophical issues should amear in THISJOURNAL.149.18 It is not a . 1197211. . consequence oE the Second Law that "regardless of &at is done to cure pollution things are bound to get worse." Even accepting that the entire material universe is a closed thermodynamic system which is by no means evident, the Second Law has no bearing on the social and political decisions that can be taken and acted upon to minimize the problems of pollution. These include decisions to terminate many of our current practices but also in gem era1 terms to develop mare efficient new technologies (and the Second Law can be used to discuss efficiency unambiguously) that will key into the overall biological ecosystem. In particular we need to develop low-temperature technology based on electrochemistry for the short run and on the truly exciting promise of the technology of superconductors in the long run. This last application still awaits the development of materials that became superconducting above t h e ordinary boiling point of liquid h y ~ drogen (20°K). To which Sheehan replies (See letter by Sheehan immediately after Heeht'sj with both wit and seriousness. . . some examples (0) Things eould be better or worse (I) You can't win. (2) You ean't even break even. (3) Stop trying the impossible. "Teaching t h e Entropy Concept," Robert C. Plumb, J. CHEM. EDUC., 41, [5], 254-256 ( M a y 1964) One might suspect that the main reason that the students do not as readily appreciate entropy as a driving force is that whereas they
concept of free energy and the change in free energy could be undertaken, but for beginning students he urges the teacher not to do so. See the next reference for more on this topic. I n "Provocative Opinion," J. CHEM. EDUC., 56, 520-522 (August 19791, two points of view a r e p u t forth.
J. A. Campbell argues "What Thermodynamles Should be Taught to Freshmen, or What is the Goal?"Rubin Battina argues
can think of internal energy in terms of potential eneigy and kinetic energy which they understand, there arena simple physical models which they can associate with entropy effects. If students understand the behavior of atoms and molecules they can find humorous examples of entropy as a driving force, but in everyday experience we lack suitable examples of entropy effects on a macroscopic scale. A maeroscopic lecture demonstration illustrating both potential energy driving forces and entropy driving forces and showing their interrelationship has heen developed and found useful. It is the subject of this paper.
Volume 60
Number 2
February 1983
105
