Luther E. Erickson
Grinnell College Grinnell, Iowa 50012
A Computer Program for the Analysis of the N,O, Dissociation Equilibrium
One of the most effective experiments for illustrating the relation between equilibrium and thermodynamic data is the NzOedissociation experiment described by Daniels, et al.' I n addition to illustrating important thermodynamic relations, the experiment provides experience in handling gases and a simple vacuum system. However, as the experiment is usually run, each student acquires only 3-4 points for a log K , versus 1/T plot. Although it is possible to pool class data for preparation of a graph containing more points or for numerical (least squares) analysis, the time required for each student to do many calculations from raw data is prohibitive while the number of steps required in the calculations often leads to errors in calculated K, values. To avoid these difficulties while introducing students to computer applications and numerical data analysis, we have prepared a Fortran I V program for analysis of data obtained by a large class. The program accepts unreduced laboratory data and writes out tables of calculated values of K , and other intermediate quantities a t each temperature for each
'~ANII:LS, F., WILLIAMS,J. W., BENDER, P., ALIII,:RTY, R . A,, COHNWI:LL, C. I)., "Experimental Physical Chemistry," MeGrawHill Book Co., Inc., New York, 1962, pp. 96-100.
student. In addition, it provides a least squares fit, of log K , versus 1/T for all students' data from which AH0 as well as ASo and AGO at 298" K are calculated. The standard error and variance of log K are also calculated. Although this program might be used in many different ways, including the checking of individual student calculations, we feel that its use by the students in the laboratory is to be preferred. I n our lab, several students do the experiment each week. Each student calculates his K , values and prepares a plot of log K , versus 1/T for his data. After all students have completed the experiment, a portion of one lab period is used for a group session devoted to a detailed analysis of the program. As part of this session, each student uses a key punch to prepare his data cards. The program is run and each student is given his output along with a copy of the data calculated for the whole class. The details of the program are then considered. This session usually leads to suggestions for improving the program. I t is our experience that this introduction to computer techniques by way of a concrete example increases student interest in both the experiment and the use of the computer. Copies of the program, including sample input and output data, are available from the author upon request.
Volume 46, Number 6, June 1969
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383
