Single-Step Reaction Kinetics Using Collision Theory
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This Demonstration considers the kinetics of a single-step reaction; an example might be the formation of hydrogen iodide [1]. Two molecules in the gas state are shown colliding with one another; hydrogen molecules (black) move faster than iodine molecules (red) since they are less massive. The rotational states are not taken into account. Two conditions must be satisfied in order for the chemical reaction to take place: correct geometry () and correct force (). The transition state is the intermediate configuration in which old bonds break and new bonds form. Three collision possibilities are considered: an ideal collision with perfect alignment (a very rare occurrence), acceptable conditions that exist within certain limits, and two unaligned molecules that cannot cause a reaction to occur. These three cases are considered for both forward and reverse reactions for a total of six possible reactions [2]. Use the "kinetic energy" slider to increase the energy until sufficient force can be reached. Then the "time" slider will show the collision in progress.
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Contributed by: D. Meliga and S. Z. Lavagnino (June 2018)
Additional contribution by: G. Follo
Open content licensed under CC BY-NC-SA
Snapshots
Details
Snapshot 1: two molecules with the correct orientation that bounce elastically because the kinetic energy is below the activation energy
Snapshot 2: two molecules with the correct orientation and a kinetic energy level that is above the activation energy start the chemical reaction
Snapshot 3: molecular collision theory applied to a case with the correct energy but the wrong orientation
Snapshot 4: molecular collision theory applied to a reaction with catalyst
References
[1] G. C. Pimentel and R. D. Spratley, Understanding Chemistry, San Francisco: Holden-Day Inc., 1971.
[2] D. McQuarrie and J. Simon, Physical Chemistry: A Molecular Approach, Sausalito, CA: University Science Books, 1997.
Permanent Citation