This SIR models a very simple reaction: one mole of reactant (red open circles) turns into one mole of product (green filled circles) and vice-versa. Examples of such reactions would be those between isomers of octane in gasoline refining.
The reactions are shown on both the microscopic (molecular) and macroscopic (laboratory) scales. This allows you to demonstrate that chemical equilibrium is dynamic. When the simulation reaches equilibrium macroscopic change ceases, but you can still see reactant molecules turning into products and product molecules turning into reactants.
This simulation can represent a great variety of dynamic phenomena, more than can normally be included in an introductory course. Some of them are quite subtle. You should try out the various options and find the ones that fit your particular presentation of the subject.
The reaction proceeds, minute by minute, as you watch, up to 30 nominal minutes. You may abort the reaction or interrupt it temporarily at any time. You may start with from 0% up to 100% reactant, and the complementary proportion of product. The reaction runs forward or backward, depending on the dynamic parameters and the initial conditions.
Dynamic parameters may be set in three modes: equilibrium constant (K) and net first order rate constant (k), Gibbs free energy change and activation energy, or the forward and back unimolecular rate constants (k+ and k-).
You may use systems of 100, 103, 104, 105 and one mole of reagents. The 100 molecule system shows considerable statistical fluctuation, which decreases as you go to bigger systems.
You may choose to replot the previous run for comparison, as shown.
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Updated July 17, 2000