LETTERS O n Unimolecular Reactions
To the Editor: The article by George Antonoff' on unimolecular reactions not only fails to clarify the subject, but adds confusion of its own. First, thestatement that "in a unimolecular reaction there must be only one molecule a t the left-hand side of the equation" is ambiguous. For example, take the familiar reaction :
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only one concentration. A unimolecular reaction is one in which the mechanism of reaction involves a change in only one kind of molecule. While the order and molecnlarity of a reaction are often the same, they need not be. One example (mentioned by Glasstonez), the reaction between hydrogen and deuterium, is bimolecular, but the order of the reaction is 1.5. W. F. LUDER NORTHEASTERN UNIVERSITY BOSTON.Mnssnc~us~r~s
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To the Editor: In the article by myself in the September number, page 420, "On unimolecnlar reactions," I noticed a lapsus in a sentence printed in italics, "should be only one molecule on the right-hand side of the equation." Instead of "right" i t should be "left." Of course, from the following text one can see that it is a mistake, because I refer to the left-hand side and not the right. To me i t appears obvious that it is a lapsus, but other readers may take a different view. G.ANTONOFF 'THISJOURSAL, 21, 420 (1914). 2 SCP.for warnple. (:LASST~SP, "Tcstbook of Physical Chemi ,FORDHAM UNIVERSITY
According to the above definition, this reaction could not be unimolecular, but actually it has long been recognized as such. Second, the article makes no distinction between the order and the molecularity of a reaction. This difference is clearly stated in a number of recent tcxtbooks.* Most of the article is concerned with first order reactions-not unimolecular reactions. A first order reaction is one in which the rate depends upon
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try." I>. \'an Nwtrand Co.. Nrs Vork. 1940.
NEWYORKCITY
