Question

I am trying to find the name of the principle that is responsible for the differences in melting points of pure and impure substances. Any idea?

Answer 1

In organic chemistry Carnelley's Rule, established in 1882 by Thomas Carnelley, stated that high molecular symmetry is associated with high melting point.

The idea behind the theory was the observation that the average amplitude of thermal vibrations increases with increasing temperature. Melting initiates when the amplitude of vibration becomes large enough for adjacent atoms to partly occupy the same space. The Lindemann criterionstates that melting is expected when the root mean square vibration amplitude exceeds a threshold value.