Mixed melting point experiment

[KVS]

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Say you have two different substances, with 2 different melting points. You mix them and then measure the melting point.

Can someone please explain on a chemical level what is happening to the molecules that decreases the mixed substance temperature- to lower than that of their individual melting points. Thanks

 

[DrknoSDN]

Melting point depression is due to decreased bonding between the two different crystal lattice structures that are present in a mixture that has solidified..

If you put a crystal of pure A and a crystal of pure B together and measured the points... They would melt at normal temperatures (separately)

This is different than if you take a solid that is a pseudo-homogenous mixture of A and B and melt it.. The mixed crystal will melt at a point lower than either one because when the lower MP is reached, the crystal lattice structure will fail. This is more commonly called Freezing point depression because it requires the creation of an impure solid so the crystal lattice does not form as easily. 2 different pure crystals next to each other is the same as if they were not even touching.