Elementary concepts of the collision theory

A reaction needs minimum energy to break chemical bindings to occur. These energies come from different forms and configurations with electron transfer and geometrical rearrangements. 

The denominator of this equation contains the partition function, which is the sum of all states and energy levels. In the case of an ideal monoatomic gas, there is only translation movement of the mass center, and the mean energy can be calculated as follows  

In this case, the partition function can be calculated, resulting in the following equation  

Note that the mean energy depends only on the temperature. 

The total energy accounts the kinetic and potential energies. The kinetic energy accounts the movement of the mass center, due to the translation movement Pcm and the movement of the reduced mass Pr- Thus, 

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