Exciting improvements in computational methods have played a significant role in advances of reaction kinetics, which range from ab initio calculations for transition states to numerical integration of kinetic schemes. Chemical systems are almost always complex, involving many reaction paths and equilibria, yet textbooks continue to present only elementary reactions and small steady-state or equilibrium mechanisms. Understanding of these elementary processes is needed, but application to larger or real systems is also valuable. Many overall processes comprise complex reaction systems that can be represented by a number of elementary reactions, where numerical integration of the elementary reaction kinetics is used for the analysis. These include combustion, atmospheric chemistry, and most industrial chemical processes. Chemical mechanisms, often involving hundreds of elementary reactions, are routinely used to predict species profiles in relation to time, or to engineer and optimize a given process.

REACT for Windows is a numerical integrator for variable-sized, simple or complex chemical kinetic systems and graphics for easy display of reactant-product species profiles. Elementary or global reactions representing a chemical system (series of chemical reactions) and their rate constants can be entered numerically (non-Arrhenius form). Initial reaction conditions (times, species concentrations) are specified and REACT then numerically integrates and graphs species profiles versus time. The program illustrates the ease with which complex kinetic systems with many elementary reactions can be evaluated, or how parameters (initial concentrations, added reactions, etc.). can be changed for evaluation of sensitivity or optimization.

Running the setup loads the program easily in default directories and installs a line in the program list for starting REACT. It is suggested to have the monitor set to higher resolution for improved viewing of the REACT page.

Like standard software, the program has both pull-down menus and icon bars for entering reactions, rate constants, initial reactant concentrations, reaction times, plot species, etc. Forward and reverse rate constants are capable of being entered (separate numeric entries) and thus included in the calculations. Data are readily entered (provided data are at hand). The program often prompts you to save your file at key steps, where subsequent process may cause you to forget to save recent changes. By prompting you, the program makes it easy to select species to be plotted.

A number of example kinetic data sets are available to the user for exercise and example. These are primarily in the classical textbook format of

A + BC <==> ABC*

ABC* ---> AB + C

ABC* + M ---> ABC + M

The current version of the program does not utilize thermodynamic data or temperature-dependent rate constants. The user or students' lab manual needs to supply the reactions and numerical values of the rate constants for use in the program. Once these data are available it takes only a few minutes to enter the reactions, forward (and reverse if desired) rate constants, initial species concentrations, and time and number of desired time steps for the kinetic integration. The program automatically keeps track of species in the kinetic scheme from the reaction equations.

A click on the calculation icon and the mechanism is numerically integrated over the specified time range and data point number. A click on the plot icon graphs the data or prompts you to select species to be plotted. It also warns you if concentration ranges are widely different, thus suggesting use of several plots with different concentration ranges. Once species are highlighted and added to the plot, re-click the plot icon to draw a graph of species profiles. I was able to enter a 10-reaction mechanism and the rate constants, review each step, correct (rename) duplicate species names (where some entered symbols were not picked up by the software interpreter), and graph results in less that 10 minutes, without using the help menu.

The program is of value in chemistry, chemical engineering, environmental science, and other courses or laboratories where kinetics is a component. The specific kinetic data, however, need to be available to the student or previously entered into the code. The REACT code illustrates and applies numerical integration of elementary kinetic reaction equations for analysis of complex (real) chemical systems.

Literature Cited

1. Booty, M.; Magee, R.; Ho, W. D.; Bozzelli, J. W. Environ. Sci. Technol. 1995, 27, 3059-3063.
2. Glarborg, P.; Chiang, H.; Bozzelli, J. W. Int. J. Chem. Kinet. 1996, 28, 773-790.
3. Lay, T.; Seinfeld, J.; Bozzelli, J. W. J. Phys. Chem. 1996, 100, 6423-6438.