Thermal stability vs melting point

[sgstudent]

An ionic compound is more thermally stable when the metal cation is more reactive. So its harder to decompose. But then what's the difference between melting and decomposition?

Also, when an compound is harder to decompose, does it mean its melting point is higher? Because even though Na2O should be more thermally stable, it has a lower melting point than MgO.

Thanks so much for the help!

 

[Borek]

But then what's the difference between melting and decomposition?

This one you should be able to answer by yourself. Cool the sample down - what will be the result in both cases?

As far as I know there is no direct connection between thermal stability and melting point. Or at least there is no universal connection - it may exist for specific types/families of compounds.

 

[sgstudent]

Oh ok. So when I say that Na2O is more thermal stable than MgO, I cannot use that to determine its melting point? Oh and is it that melting is a physics change while decomposition is a chemical change?

Thanks Borek!

 

[Dr_Morbius]

Oh ok. So when I say that Na2O is more thermal stable than MgO, I cannot use that to determine its melting point? Oh and is it that melting is a physics change while decomposition is a chemical change?

Exactly. There is no connection between meting point and decomposition point. When a substance decomposes it is no longer the same substance it was before it decomposed. It is now a different substance.