This applet models the Lindemann-Hinshelwood mechanism for the kinetics of the unimolecular reaction A ⇔ A* ⇒ P in the gas phase. The rate constant for the collisional activation of A is k1: A + A ⇒ A* + A. The rate constant for the collisional deactivation of A is k-1: A* + A ⇒ A + A. The rate constant for the formation of product(s) P is k2: A* ⇒ P. The mechanism presumes that the activated molecule A* is formed only by collision, and that P never reverts to A or A*. To solve for the over-all rate law, the steady-state approximation is made; i.e., d[A*]/dt = 0.
The mechanism is depictly visually on the left-hand side of the applet. The blue spheres are the unactivated A's, the red spheres are the activated A*'s, and the green spheres are the product P. No inference is to be drawn from the rates of reaction depicted in the graphic - it is intended only to demonstrate the steps involved in the mechanism.
This applet models the unimolecular reaction stochastically, by comparing a randomly generated number with the rate constant each small time interval. When the random number is less than the rate constant multiplied by the time interval, the event occurs. Because of the stochastic nature of the simulation, there is no need to prostulate the steady-state approximation; in fact, the concentration of intermediate A* can be observed over the course of time, to verify how well the approximation holds.
Click on the appropriate button below to increase/decrease the concentration of A ([A]), or any of the three rate constants k1, k-1, or k2.
© 2003-2011 by Lawrence T. Sein. All rights reserved.
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