The program simulates a chemical kinetics experiment in which the student investigates the following reversible reaction:

A + B C + D

The objective is to:

1. Find the order of reaction with respect to each of the reactants, n_A, n_B, n_C, and n_D.
2. Find the values of the forward and reverse rate constants, k_f and k_b, at one or more temperatures.
3. Find the values of the forward and reverse activation energies, E_f and E_b, in kJ/mol.

The isolation method, first devised by W. Ostwald, is used to find the reaction orders and rate constants. The program provides log and reciprocal plots of the concentration versus time data so that the reaction rates can be determined graphically. The concentration versus time data can also be saved to a file for more sophisticated data analysis with a spreadsheet or stand-alone statistics program.

The Arrhenius equation is used to find the activation energies. If the kinetic parameters are determined at more than one temperature, advanced students with knowledge of physical chemistry can also calculate ΔG_T°, ΔH°, and ΔS° for the overall reaction. The parameters for the reaction are chosen from 160,000 different sets available, using a code based on the letters in the "unknown" name.

Figure 1. The simulation screen in KinSimXP.

Figure 2. Sample data plots from KinSimXP.

Experience using KinSim has shown the precision of the student results is not as good as it could be, but, it is much better than using the data students get from their "real" kinetics labs. Attempts to improve the precision of their results by using Excel to plot the graphs and find the least squares slopes led to less understanding of the process and precise, but inaccurate, results. Many students had no concept of how to find the slope of a noisy graph by hand or how to define or measure the slope.

Linear least squares (as done by Excel, etc.) is the wrong way to analyze kinetics data in the presence of significant noise (3). The error estimates in the kinetic parameters generated using linear least squares are wrong. Students get upset when the rate constants and error estimates produced using linear least squares do not give the real result. Doing the graphs by hand from the printouts made by KinSimXP allows the students to get a feel for the accuracy of their results in the presence of the noise amplified by the linearization process, gives results as accurate, though not as precise, as Excel, and provides a much more meaningful laboratory data analysis experience.

In advanced or honors chemistry classes or in physical chemistry, KinSimXP can be used to generate data for proper analysis by nonlinear curve fitting using a Mathcad template (3) or a commercial statistics package. Thus, KinSimXP's lack of automated data analysis is an advantage. It generates data for later analysis, that the student can use with whatever data analysis procedure is appropriate.

Literature Cited

1. Merrill, J. C.; Spicer, L. D.; Brown, R.; Walling, C. J. Chem. Educ. 1975, 52, 528.
2. Allendoerfer, R. D. Chemical Laboratory Simulations; ComPress, a Division of Queue Inc., 1989. Program KinSim was adapted from a program described in J. Chem. Educ. 1975, 52, 528 with permission from J. C. Merrill, L. D. Spicer, R. Brown, and C. Walling, Department of Chemistry, University of Utah, Salt Lake City, UT. (No longer available.)
3. Zielinski, T. J.; Allendoerfer, R. D. J. Chem. Educ. 1997, 74, 1001-1007.

For more information, see the General Chemistry Collection home page.