Formulas and Equations Daniel Blshop Custom Comp P.O. Box 429 Buena Vista, CO 8121 1 R.
Formulas and Equations is a set of three programs for the TRS-80. I t provides tutorial instruction and problems on balancing chemical equations, on stoichiometry, and on determining the validity of and structure for formulas of organic compounds. Each program provides step-by-step instruction on the correct solution to each missed problem, as well as worked examples that may be selected for viewing a t the student's option. All problems include randomly generated elements. TRS-80 graphics allow chemical formulas to be displayed in conventional format, with lower-case letters and correctly positioned subscripts. The three programs are on a single cassette and require a 16K Model I TRS-80 with Level I1 BASIC. The cassette, student handout, and instructor's manual (including complete listings) are available for $50. For more information write to the author a t the address above.
Equilibrium Demonstration and Linear Data Plotting Willlam J. Mueller Univeristy of Wisconsin-Stout Menomonie, WI 54751 The programs described below are designed for use in introductory college chemistry courses (non-majors). The first is a demonstration program for use by students individually or for instructor-class demonstration. The second is for student use in laboratory data analysis where linear plots are desired. Equilibrium Demonstration. A concept in introductory chemistry that is often hard for students to visualize is equilibrium. - ~ n c r o s c o ~ irlrmonstratiuns. c such as showing changes in indicator colors associated with pH changes, serve to show that reactions are revenible. The equilibri&constant is introduced as a method for showing the relationship hetween reactant and product concentrations a t equilihrium, again using macroscopic variables. The microscopic concept of eauilibrium isdiscussed but is often difficult to illustrate and ditiicult for the student to visualize. This prngram isdesignrd to illustrat~.the effect of therize oi an rquilihrium constilnt and of 1.e Chatelier's Principle on the reactsnt~uroductdistribution for a generalized reaction: A B F? C. A computer graphics/dispiay of such a system shows initially 25 "molecules" of A and 25 of B being added to a container. Tbese molecules are then "mixed," allowed to "read," and reach equilihrium. The equilibrium distribution of A's, B's, and C's is then examined and tabulated. This cycle iscarried out for values of the equilibrium constant K = 1,0.1, and 10. To illustrate Le Chatelier's Principle, the reaction utilizing 25 A, 25 B, and K = 1is re-examined. The system is allowed to reach equilibrium. An additional 10 C molecules are then added. allowed to react. and allowed to reach eouilibrium. The reactant product distribution is again examined to note the effect of the added nroducr. The urorram terminate* with a short summary of t i e major ideas presented by the illustrations. Linear Data Plotting. Occasionally a simple, easy-to-use microcomputer program for plotting straight lines would be of immense value to introductory chemistry students. Poor mathematical backgrounds tend to be the rule for these students and therefore struggling through linear data analysis may be counterproductive if the chemical principles are'the important aspe&. This simple program uses an unweighted least squares (7) treatment of data to calculate the best fit line through a series
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Journal of Chemical Education
of student supplied data points. Up to 14 data ( X , Y)values are allowed. The program calculates the slope and intercept of the line and the standard deviations associated with them. It also calculates the best fit Y value for each X value for student use in plotting. A graphical display of the data points andlor the best fit line through the points is a student-selectable option. (The program sorts the X and Y values and scales them to an aribitrary 0 to 100 scale for display.) The utility of this option is that it serves to visually illustrate the fit of the line to the data points and can be instructive with respect to the quality of the data supplied. Both programs are written in BASIC (specifically Level I1 BASIC for Radio Shack TRS-80 Model I, 16K Level 11.)The eouilibrium demonstration Droeram utilizes the unioue gkphics commands for the TRS-go and would not be read'iy trilns~ortahleto other svstems. It uses 9.8K oid bit words. The linea; data program uses 3.7K 8-bit words and also utilizes TRSdO graphics. This program should be readily adaptable t o the graphics capabilities of the system being used. Cassette tape copies of both programs suitable for use on the Radio Shack system described ahove are available for $10.00 from the author a t the address above. Check or purchase order should be made to the Department of Chemistry, UW-Stout.
Perspective Projections of Function Surfaces Russell H. Ban Kenyon College Gambier, OH 43022 Physical chemistry students often experience considerable difficultv visuali~ingthe three dimensional surfaces resultinr! from the evaluationof atomic or molecular wave and ch& distribution functions over planes through the atom or molecule. The program PLOTXY was written to produce on a graphics terminallplotter perspective projections of such surfaces, viewed from various orientations. A recent article by David (17) illustrates the utility of such plots. Our students have found these ~ersnective ~roiections to be a valuahle . . . . supplement to the contour and dot density representntlons of wa\~eiunctionscummonlv found in texts. In addition. hecause the program is run in a time-sharing mode, our students can actively explore the effects of changing wavefunction parameters, and of forming various hybrids and linear combinations of atomic orbitals and other basis functions. Our students can thus visually investigate a greater variety of wavefunctions than illustrated in most texts. Although PLOTXY was written primarily for representing wavefunctions, it can be used more generally for any single-valued function of two variables and thus is quite useful in many chemistry, physics, and mathematics courses. The program PLOTXY evaluates a user supplied function, f ( x y ) , over a grid of points in the xy plane to produce slices through the function surface parallel to the x and y axes. These slices are then rotated around the x axis (horizontal terminal screen axis) and t h e y axis (vertical screen axis); subjected to a perspective projection onto the plane of the terminal screen with the viewpoint located on the y axis toward the ohserver; and finally displayed on the screen or bard copy plotter. Before display, the hidden lines are removed by an improved version of a FORTRAN algorithm written by Watkins (8). The user interacts with PLOTXY as follows. After execution has begun, the user is instructed to enter the BASICPLI'S code nrcessary to evaluate the function. The program waits until this rode has been entered and verified hy thr urer. Execution continues and control passes to the input menu. Here the user enters input parameters: the x , y values defining the xy domain over which the function is to be evaluated, two rotation angles, and a scaling factor by which the display may be vertically expanded. The input menu also allows the user
