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THE PROBLEM METHOD OF TEACHING PHYSICAL CHEMISTRY* MILESS. SEERRILL, M A S S A C ~ SINSTITUTE E~S OE TECHNOLOGY, CAMBRIDGE, MASSAWSETTS One may acquire enthusiasm for the game of tennis by watching a Bill Tilden play. In order to have a chance of defeating him, however, one must step from the. bleachers to the courts and be taught how to swing a,racquet. It is the same with Physical Chemistry. A student may acquire enthusiasm by attending a course of lectures presented by some outstanding leader in the field of chemistry. But in order to "play the game" of chemistry, he must be taught to apply chemical principles to the practical problems of every day. I, personally, believe that this result is best achieved by a well-planned problem course of instruction. I can perhaps best express my views by outlining briefly the type of course which has been developed by Dr. A. A. Noyes and me for college students .yho have already had good general courses in physics, mathematics, and chemistry. The course is planned not merely to impart information, but to make the student think about the principles presented by demanding that he work out for himself the method of treatment of special cases on the basis of these principles. In explaining the nature of the course to my own students address them somewlpt as follows: "In order to become a good practical chemist you must not only know what the fundamental principles of chemistry are, but you must acquire the ability to apply these principles. This ability can be acquired only by your own personal effort, but I can help you by assigning carefully selected concrete problems involving the principles. You will find that these problems are not merely supplementary or incidental to the text, but are the main feature about which the whole presentation centers. They are not grouped a t the end of a chapter, but are interspersed throughout the text. As a rule they are not the usual type of problem involving substitution in an equation and mathematical operations, but will require clear logical thinking in the application of the principles under consideration. In other words, it is a problem course of instruction, not merely a course with problems. You may not be able to solve every problem, but you will gain from having given thought to it, (just as you gain most in tennis by playing with some one who can beat yon). My r81e as teacher will be mainly to act as guide and to help you help yourselves.''
* Contribution to the symposium on "The Teaching of Physical Chemistry," held by Divisions of Physical and Inorganic Chemistry and Chemical Education, at the 76th Meeting of the A. C. S., September 11,1928, at Swampscott,Mass.
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These problems form the basis of the classroom discussion. Definite problems are assigned which are to be solved and handed in a t the beginning of each exercise. My own procedure is to solve the problems on the blackboard, questioning the class as to how to proceed. It has been our aim to make each problem serve a definite purpose, this purpose being indicated by giving each problem (or problem group) a title. It is therefore not difficult to lead the class into a general discussion of principles. In a successful exercise the individual members of the class may ask rather difficult questions. As a rule I appeal to the better men in the class to answer. If I myself am unable to answer the question satisfactorily, I freely admit my ignorance but always try a t the next exercise to clear up all doubtful points. In the course of my teaching I have learned a great deal from my students in this way, i n d I like to think of my course as a "companionate" course of instruction. I do all in my power to foster this spirit. The more difficult problems naturally arouse the most interest. The very simple problems, especially those of the substitution type, are discussed very briefly, if a t all. I ask my students not to take notes in the class. To discourage this habit I point out that the essentials are clearly stated in the text, and that it is far better to give concentrated thought to the discussion during the exercise than to copy down minor facts to be thought about later. The problems which are handed in are marked, but not corrected, and returned promptly to the student: Though I discourage a student from taking notes, I do suggest that he keep p complete file of problems correctly solved. It is important in a course of this character to give frequent written tests consisting mainly of problems differingfrom those solved in the class but involving the same principles. This serves not only as an excellent review, but it forces you, as well as your students, to take account of stock, so to speak. In this way any doubtful points are discovered and made clear before new topics are discussed. At times, when it seems desirable, I lecture informally, but always with the understanding that I am to be interrupted if I do not make myself clear or if any relevant question arises. Of course I reserve the right to judge whether the question is relevant; for one has to deal with the "smart Alec" type of student, and the type unable to put a question dearly. In this way it is possible to allude briefly a t least to the experimental, research, and historical aspects of the subject. Collateral reading of reviews and original articles in the chemical periodicals, or of textbooks in which these aspects are more fully discussed, should be definitely suggested. In our revision of "Chemical Principles," Dr. Noyes and I are planning to make definite suggestions, by giving what we call "Reading References" a t the end of each chapter. Such references are of special importance to students who are planning to go on to graduate work.
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It is very desirable to have this classwork accompanied by a brief laboratory course and by lecture experiments. I believe that the primary purpose of such experiments should be to give concrete illustration of the basic phenomena under consideration rather than to emphasize the experimental methods by which physico-chemical properties are determined. In my own course I have tried to make each experiment resemble a short research so planned that with the apparatus ready a t hand, as well as all necessary stock and standard solutions, it may be completed within two or three hours. Our chief difficulty is to get the student to think about the experiment before he comes to the laboratory, and to prevent him from blindly following directions. Yet we find i t necessary to give detailed directions if we are to exact good resultsin so short a time. We have tried various expedients to insure preparation in advance. The best method, but one difficult to enforce, is to require a data sheet, made out in blank form, in advance. We have also given out problems based on experimental data to be solved. But i t is human nature to put off till tomorrow, so we always hold a brief conference in the laboratory in which are discussed the reasons for the details of procedure and the chief sources of errors. Our hope is that the student will then intelligently perform the experiment with but an occasional reference to the directions. A more leisurely attitude toward a laboratory course is much to be desired. A problem course of this character is necessarily more time-consuming than a descriptjve course. For this reason Dr. Noyes and I were forced to omit some of the subjects usually considered in the more descriptive courses. We selected those subjects which we considered of the greatest practical importance to chemists. We first develop the atomic, kinetic, and ionic theories through a consideration of the physical properties related to them, and then with the aid of these theories we present the principles related to the rate and equilibrium of chemical reactions from mass-action, phase, and thermodynamic viewpoints. The very important and fascinating newer theories of atomic structure and radiationwe postpone to more advanced courses. You may be interested to know that in our revision of "Chemical Principles" we are planning to publish our book in two volumes; the first covering the elementary part and the second the more advanced. In the second volume we treat more fully thermodynamic chemistry, and hope to develop by the same problem method some of these newer theories. In conclusion let me state that I am convinced from my own experience that such a problem course does develop in the student the ability to think logically and lays a firm foundation for the more original kind of thinking that goes with research.
