This model demonstrates a conception of thermodynamically allowed reaction as well as a linkage (relation) of this conception to the main thermodynamic functions. You may modify parameters of the model reaction by rolling buttons of entry spaces and observe how they modify the Gibbs energy that may be either absorbed or liberated. All essential in this case thermodynamic potentials (enthalpy, Gibbs energy) as well as a product of entropy and temperature are represented by column diagram in the window in the right part of the model. During study of the model you may see that the reaction is thermodynamically allowed, i.e. it is possible, when an increment of Gibbs energy is negative, the only. However, one should remember that under adverse conditions a rate of reaction may be too low. In that case an increase of temperature or an addition of catalyst may provide a production of noticeable amount of the reaction product. Remarkably, the temperature increase may either transform an allowed reaction into forbidden one or vice versa.