Melting Point of Amorphous Solids [closed]








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My textbook says that amorphous solids do not melt at a fixed temperature,but at a range of temperature. It depends on the way the atoms/molecules are present in a given piece of solid. 
  

Since the melting point(range) depends on the whole solid piece , can it be said that melting point of amorphous solid is an extensive property?




No matter how the structure is the heat given to the substance will be distributed over many molecule/ atoms. And the all molecules will more or less the average energy. So, on average temperature will be same across the substance. This will happen even if the substance does not conduct heat well but on a smaller region.


For breaking a bond, you need specific amount of energy. Boiling or melting needs a lot of bonds to be broken. Most molecules, on average will gain that energy on a specific temperature.


So, that being said, the m.p. and b.p are not extensive properties. Being amorphous or crystalline doesn't change the reasoning.


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The question mixes two concepts.


* As correctly stated by @Ivan Neretin and @Mockingbird, "melting point" is an intensive property, that does not change if you have 5 g or 200 g of a material. (See for an explanation for example [here](https://en.wikipedia.org/wiki/Intensive_and_extensive_properties).)
* There are many instances without sharp transition solid -> liquid, resulting what is called [glass transition](https://en.wikipedia.org/wiki/Glass_transition). This is what your textbook likely refers to (first phrase of your question).


Polymers in general are one example, DNA and some proteins do not melt either and show reversible glass transitions. (If you iron a shirt, you benefit from glass transitions, too.)


In contrast *some* small molecule crystalline materials undergo irreversible glass transitions , while heating up to the melt there is one large (across several K) range of phase transition; but after cooling the molten sample and re-heating, only a sharp melting point is observed.


You may monitor glass transitions indirectly by observing the intensity of fluorescence in function of the rising temperature; often used in DNA chemistry, for example. Or you heat your sample gradually in reference with a known sample to compare with, by [differential scanning calorimetry](https://en.wikipedia.org/wiki/Differential_scanning_calorimetry), the more general method.


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