Enhancing the Concept of T, p, and p as lntenslve Properties
To the Editor:
Multlple Cholce Testing
To the Editor: THIS JOURNAL has recently puhlisheda note [Aronson, J.
N., Krause, E. C., J. CHEM.EDUC.,59,381 (1982)l on the topic of the Coombs Response Mode of scoring multiple choice tests. Experiments utilizing other scoring methods with chemistry students' and nutrition students2s3 have recently been reported in relatively accessible journals. Cross et all investigated "choice weighted scoring" in which partial credit is assigned to some of the incorrect options in a multiple choice item. Akeroyd2investigated a "Dual Response System" in which the examinee is allowed to make TWO resnonses if s h e wishes receiving HA1.F a mark if ONE rrsponsk is correct. The rntionale behind this svatem is KIeliminate random fluctuations from lucky or u n l u k y guessing rather than award credit for partial knowledge.
As stated by Tykodi (J.CHEM.EDUC.,59,557 (1982)), the standard proof of Euler's theorem used in thermodynamics courses is frequently found "mysterious" or "tricky" (or both!) by some students. Since the theorem usually appears in the most formal part of a thermodynamics course and yet it is one of the first bridges between formalism and more "useful" equations, one should try to bring in a t this point the most physical insight possible. I have been using an approach which is essentially Tykodi's, enhanced with the following modification. The most "mysterious" or "tricky" point in the derivation is setting A = 1in eqn. (28) of Tykodi's paper. Yet this step is not necessary while dealing with n = 1, since in this case [~F(.z:)I~z:],.,
= [a~(~~)iax~],,
(1)
(this corresponds to eqn. (9) in Tykodi's paper). This equation is simply astatement of the fact that T, p, and@are intensive properties. If eqn. (1) is substituted in eqn. (28) for n = 1, eqn. (29) follows immediately. Thus, the concept of intensive property is underlined while making the proof more physical and more intuitively appealing. The procedure is trivially extended to n f 1, but the theorem is used only for n = 1 (extensive properties) in thermodynamics courses.
F. M. Akeroyd
Alelandro Plsantv
Bradford College West Yorkshire, England BD71AY
D. E. Pg, Fac. de ~ u i m i c a U.N.A.M. DelegacBn Coyoachn 04510 MBxico. D.F.. MCxico
' Cross L. ti., Ross F. K., Geller E. S., J. ~ x p ~. d u c . ,48, 296,
119801. ~ ~ -
-
~ieroydF. M., Nut. FoodSci, 14 (JanlFeb 1981). Akeroyd F. M.. Nut. Fow' Sci.. 18 (NovIDec 1981)
To the Editor; Teachers of thermodynamics should take note of the procedure suggested by Pisanty-it is a special case (n = 1) of the general procedure used by Pierre Duhem: D. G. Miller, J. CHEM. EDIIC.,40,648 (1963). I thank Donald G. Miller for calling Duhem's procedure to my attention. R. J. Tykodl Southeastern Massachusens University North Dartmouth, MA 02747
Concurrent Reactlons
To the Editor: In the "Chemical of the Month" article on titanium dioxide 1982) the equation fur the manw facture of titaniumrlvj . . rhloridc- is balnncrd orbitrnrilv in unr of many ways because it is a combination of two concurrent reactions. ITHISJ O U R N ~ February I.
By multiplying (1) by any coefficient such as 1,2,3, etc. and (2) hy any coefficient such as 1,2,3, etc. and adding the two resulting equations a third is obtained which is only one of an infinite number of possibilities such as the following two
Concurrent reactions, as in the case of titanium(1V) chloride, should be written separately. H. I. Felnstein 10411 Forest Ave. Fairlax, VA 22030
Why van Deemter Parameters?
To the Editor: The publication of Moody's experiment on the evaluation of the parameters in the van Deemter Equation' provokes the question why anybody would want to determine them. The exercise seemed desirable 20 years ago when chromatographic theory was developing, hut the ensuing decades have shown that the equation is unreliable, the A term mainly represents errors in measurement, and the effect of the instrument injection system invalidates the measurement in any hut the most sophisticated systems. Moreover.. the Darameters have not moved useful in makine . real-world decisions in the design of analyses. I have ronsulted a number of ~ractirionerswith a solid knowledrr of the theon who have assured me that they get results quicker from H qualitative understandine of the forces involved in retention and dispersion combinediith a seat-of-the-pants judgment than they can from calculation The siiuat ion is different for designers of instruments and for high-level researrhers inrent on generally improvingcurVolume 61
Number 5 May'1984
475
