INTERMOLECULAR FORCES AND INTERACTION ENERGY 



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vidual pairs of interacting molecules may have widely different kinetic 

 energies; a certain fraction will possess kinetic energy greater than cp^ 

 and the molecules will not be associated. The average energy of interaction, 

 or the decrease in energy involved in bringing the molecules from infinite 

 distance apart to their equilibrium separation, will however be (p^ since the 

 total kinetic energy does not change. The average equilibrium distance 

 between the molecules, d^, will differ from d^ by an amount dependent on 



Fig. 6-9. Generalized energy curve to illustrate the mean time- 

 averaged distance between interacting groups due to thermal 

 kinetic energy. For the interaction between an ion and a dipole 

 obeving the equation: 



(p = lOVc^i' — 57.4/^2 



the distances may be calculated to be: d-^ = 3.63 A, d^ = 4.00 A, 

 do = 4.43 A, da = 4.82 A, and d^ — d^ = 1.19 A. 



