LETTERS T o the Editor: T o the Editor: In the February issue of THIS JOURNAL, George The suggestion by Antonoff' that the definition of a Antonoff attempts to evade my criticism of his article first order reaction given by Luder2 "must be modified" on reaction rates which appeared in the September is, by implication, a criticism of the definition given issue. In doing so he runs into a real blind alley by in my own writings.8 I feel called npon, therefore, stating that "the first order reaction is one in which the to make some comment on the subject. May I say rate depends npon only one substance, irresfiective of a t the outset that I agree completely with Lnder's concentration." (Italics mine.) remarks, and endorse his view that Antonoff's first Now if there is one thing agreed upon by all the letter4 added confusion to the situation. The second authorities and all the textbooks, it is that the order of letter, referred to above, makes i t even worse! a reaction is the number of concentration factors which Antonoff implies that the rate of a first order reaction, enter into the rate equation. A h t order reaction is like that of a radioactive change, is independent of the one whose rate is given by the equation concentration. Surely this is due to a misunderstanding of the term "rate." In reaction kinetics it refers to dc/dt, the rate of change of concentration, and not to dN/dt, the rate of change of the number of molecules. which, when integrated, leads to the exponential equa- I t is the latter, and not the former, which is independent tion of the concentration in a tirst order reaction. C = CacW Incidentally, to state, as Antonoff does, that "we do not know the actual mechanism" of the decomposition I venture to say that Professor Antonoff is the only of nitrogen pentoxide is to disregard the many imporperson who ever stated that the rate of a first order tant researches on this subject. If there is one gas reacreaction does not depend upon concentration a t all! tion that students of chemical kinetics would unhesiHowever, the source of confusion is a quite common tatingly accept as unimolecular, as well as first order one, which even occurs in one physical chemistry textdown to quite low pressures, surely it is the decomposibook. It is evident in Professor Antonoff's discussion tion of nitrogen pentoxide. of radioactive change. It is true, as he says, that the While expressing great respect for Professor Anrate of radioactive disintegration does not depend upon concentration. But it does not follow therefrom that tonoff's contributions to science, especially in the field of first order reactions do not depend npon concentration. interfacial tension, I would suggest that readers of the EDUCATION disregard his reThe difficulty is that the exponential law of radio- JOURNAL OF CHEMICAL marks on unimolecular and first order reactions. active change is stated in terms of weight of material decomposed-not concentration, which remains the same. According to the universally agreed-upon definition of a h t order reaction, radioactive decomposition is not a fist order reaction in concentration since its rate does not depend upon concentration. THISJOURNAL, 22,98 (1945). Ibid., 21, 559 (1944). W. F. LUDER a GLASSTONE. S.,''Textbook of Physical Chemistry." D. Van Nostrand Co. Inc., New York. 1940. THISJOURNAL. 21, 420 (1944).
COOPERATIVE ORGANIC CHEMISTRY TESTS The revised mimsogmphed edition of the preliminary d m f t of Form V of the Cooperative Organic Chemistry Test, sponsored by the Division of Chemical Education and the American Council on Education, is now asailable to instructors of organie chemistry who are willing t o collaborate with us i n the validation of this test. Both tests and answer sheets, for mechanical scoring, will be supplied without charge upon request, provided the answer sheets are returned to the chairman of the committee for the purpose of obtaining dam o n ualidity. The results of this testing program should be i n the possession of the committee not later than August 15, 1945, as the final form of this examination will be drafted during September. If you can give this examination t o either yourfirst- or secondterm students i n organic chemistry any time before the 15th of August, your cooperation will be appreciated. Requests for this test, specifying the number of students t o be tested, should be F. Degwing, C h a i r m n of the Committee plaeedassoon n a r w o ~ n n b l y ~ o s s i bwithEd. le on Organic Tests, Department of Chemistry, Purdue University, Lafoyette, Indiana.
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