Science Poetry

Collision Course

“A threefold kinetic provision:
Reactants in proper position
With energy sufficient
And run-ins efficient 
Achieve a successful collision.” 

The 26 April 2022 Twitter limerick provided an overview of collision theory, which is used in chemical kinetics.  The field of chemical kinetics is concerned with the rates at which and mechanisms by which chemical reactions occur.  

“A threefold kinetic provision…”

 Kinetic theories are those that rationalize gas behaviors based on the motion of the molecules involved.  These theories consider gas molecules as hard spheres to simplify their treatment, essentially treating molecules as infinitesimally tiny billiard balls.  This helps explain why “collision” is the primary term used to describe molecular encounters.     

Collision theory points to three main criteria (“a threefold kinetic provision”) for considering whether a chemical reaction will successfully transpire. 

“Reactants in proper position /
With energy sufficient /
And run-ins efficient…”

The idea of collision theory is that for molecules to react with one another, they have to successfully collide with (encounter) one another. 

The three criteria explored in collision theory are generally referred to as the collision requirement (are molecules encountering one another in the first place?); the energetic requirement (will a pertinent collision occur with enough energy to overcome the activation barrier?); and the steric requirement (will the molecules that collide with one another have the proper three-dimensional arrangement in doing so)?  

In verse form, the collision requirement becomes “run-ins efficient”; the energetic requirement becomes “energy sufficient”; and the steric requirement becomes “in proper position.”  

Achieve a successful collision.” 

If all three of these criteria are met, the particular molecular encounter can proceed from reactants to products: the collision has been a “successful” one.   

(As in the case of many other posts on this site, a primary goal with this poem is to help chemistry learners organize a great deal of information!  The nuances and details, of which there are many, can follow once the big picture makes more sense.)