Abstract:

In this work, we present an interactive application (App) to explain the relationship between chemical kinetics and chemical equilibrium(1), as well as their dependence on reaction mechanism and initial conditions(2). Some additional concepts such as steady-state, chemical balance or oscillatory regime (clock reactions) are naturally presented(3).

The App has been developed by our group, based on Mathematica software, and its adressed to first-year college students in the degrees of Pharmacy, Biotechnology or Biomedicine.  

For a specific set of reactions, chemical pathways can be forced to different regimen behavior by tuning the initial conditions (reagent concentrations) or the kinetics constants (reaction conditions). In fact, multistep reactions are very sensitive to small variations of initial conditions and chemical enviroment. The aim of this APP is facilitating the student, in terms of virtual representations, to get familiar with these concepts and help them to infer how different regimens can be achieved. 

The App presents a graphic interactive interface where the students can vary many different parameters involved in the reaction. In particular, we have chosen the following coupled model reactions:  
A →X
B+X →Y+D
2X+Y→3X
X→E

Based on the above reactions, the students can modify the reagents concentration (A and B) and the reaction velocity through the constant kinetics (k1 to k4) to see how the production of the intermediates (X and Y) and the products (D and E) vary due to the previous mentioned changes. The result of the modifications is shown in graphical mode, as we consider it is a more intuitive way to interpret and visualize the results than numerical mode. In particular, the graphical representation consists of two graphics and a movie of an Erlenmeyer flask. In the first graphic, the concentration of reagents, intermediates and products are plotted as a function of time. In the second one, a parametric representation of intermediates evolution. The monitoring of the reaction in terms of the involved intermediates also allows studying the reaction at infinite time, differentiating the situations in which the system advances to a state of thermodynamic equilibrium, the situations in which the reaction evolves until the appearance of a stationary state or situations in which the reaction enters a situation of oscillatory regime. Finally, the Erlenmeyer flask represents the variation of the reagents occurring during the simulation, where the content color changes with the different chemical species and kinetic regimens.  This allows correlating the graphics with the simulated reaction. Thanks to that, the students can create a very intuitive picture to understand the specific way that changes in the reaction concentrations or in the kinetics contacts, affect the obtained products and equilibrium or non-equilibrium regimens.

In summary, the developed application is a very useful tool to help students to understand and interiorize kinetic concepts by experience the relation between reagent concentrations, velocity constants and products obtained in a general set of chemical reaction.  
   
References:
[1] Atkins, P. & Paula, J. de. Physical Chemistry. Freeman, W. H. & Company (2014).
[2] Pilling, S., Seakins, P. W. & Pilling, M. J. Reaction Kinetics. Oxford Science Publications, (1996).
[3] Field, R. J. & Schneider, F. W. Oscillating chemical reactions and nonlinear dynamics. J. Chem. Educ., 66 (3), 195 (1983).

Keywords:

Chemical kinetics, application, virtual learning.