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JOURNAL OF CHEMICAL EDUCATION
'
FEBRWNZY, 1932
DEAREDITOR: The method of balancing chemical equations "algebraically," presented in your issue of December, 1931 (p. 2453), is probably derived from Sir James Walker's textbook, "Introduction to Physical Chemistry" (Macmillan & Co.). The earlier editions of this well-known volume contain a brief chapter (Chapter 111) on Chemical Equations which, significantly enough, opens with a discussion of the reaction exemplified by your correspondent: ? Cu
+ ? HNOa+? Cu(NOJs + ? NO + ? HIO
Although this particular equation is not solved by algebra, the algebraic method is developed a t the end of the chapter in.connection with a still more complex reaction : e K.CrsOl
+ b FeC12 + c HCI -+d KC1 + e CrCIa + f FeC18 + g H20
The method certainly works admirably for this and similar reactions, but Walker is careful to add: "The student of chemistry is not recommended to make use of the algebraic process, as it is purely mechanical and affords little insight into the nature of the chemical reactions considered." The latest (tenth) edition of his book omits the chapter entirely. Very truly yours, JAMES KENDALL CHEMISTRY DEPARTMENT UNIVERSITY OF EDINBURGH EDINB~RGH, SCOTLAND
?
DEAREDITOR: In reply to Mr. Endslow's inquiry (page 2453 of the December, 1931, JOURNAL OF CHEMICAL EDUCATION) regarding the algebraic method of balancing chemical equations, I should like to offer the following information. In a text named "Introduction to Physical Chemistry," by J. Walker, LL.D., F.R.S., Professor of Chemistry in the University of Edinburgh, 8th edition, Macmillan & Co., St. Martin's St., London, in the very first chapters may be found two to three pages of good explanatory material on the subject. The method, apparently a very old one, is also discussed in the first edition, published about 1899. There really is a basis for this scheme, for certainly a relationship exists between these letters, as used in forming many equations. However, the amount of algebra employed and the many, many equations that must be used in balancing the oxidation and reduction (in acid solution or basic
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solution) makes it almost impossible for practical use. It surely would be a very good hobby for any one interested in chemistry to keep in mind. Very respectfully yours, ARTHURR. CLARK FRANKLIN AND MARSAALL COLLEGE LANCASTER, PENNA. DEAREDITOR: The algebraic method of balancing chemical equations set forth in the recent communication of A. W. S. Endslow U. CHEM.EDUC.,8,2453 (Dec., 1931)l requires the solution of as many simultaneous linear equations as there are substances symbolized in a given chemical equation. It follows that there must be a t least (n- 1) different elements involved in a chemical equation of n substances, since one algebraic equation is formulated for each element, and in addition, a is set equal to one. This requirement is met by many, but not by all, chemical equations. For example, cannot be balanced by this method, since i t is possible to formulate only six independent linear equations, whereas seven are necessary. Very truly yours, NICHOLAS DIETZ,JR. TnE UNIVERSITY OF PITTSBURGH P I T T ~ B ~PENNS~VANIA GH, T DEAREDITOR: From time to time I see in the JOURNAL OF CHEMICAL EDUCATION and other magazines articles on methods of balancing equations. The one occurring in the correspondence section of the December, 1931, issue of THIS JOURNAL (p. 2453) caused me to submit the method I have used in my general chemistry classes for a number of years. This method seems simple to me, though my description may appear involved. My students have had very little trouble using it on even the most difficult equations. It might be helpful to others. I classify reactions in three groups as follows: Case No. 1. Reactions that are non-oxidation-reduction or simple oxidation-reduction. Case No. 2. Oxidation-reduction rextions in which one element is oxidized and one reduced. Case No. 3. Oxidation-reduction reactions in which two different elements are oxidized or reduced and, in rmjunction, one or two reduced or oxidized.
