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When do we say that a compound is thermally stable? I was studying the properties of compounds of alkaline earth metals and somewhere in my textbook it was written, "The solubility, thermal stability and basic character of hydroxides increases with increasing atomic number from Mg(OH)2 to Ba(OH)2." I was totally confused as to how the thermal stability and solubility of compound increase simultaneously. I am not able to understand what thermal stability even is and how it is contrasted with solubility.

When do we say that a compound is thermally stable?
 
I was studying the properties of compounds of alkaline earth metals and somewhere in my textbook it was written, "The solubility, thermal stability and basic character of hydroxides increases with increasing atomic number from Mg(OH)2 to Ba(OH)2."
 
I was totally confused as to how the thermal stability and solubility of compound increase simultaneously. I am not able to understand what thermal stability even is and how it is contrasted with solubility.

Grade:11

1 Answers

Rajdeep
231 Points
5 years ago
HELLO THERE!
 
Thermal stability of a compound refers to how stable it is to heat: a compound is called thermally stable if it does not decompose even at strong heating.
 
Consider Lithium carbonate and sodium carbonate as examples.
We cannot say that Lithium carbonate is thermally stable because when Lithium carbonate is heated, it decomposes to give lithium oxide and carbon dioxide gas.
However, sodium carbonate is thermally stable because it does not decompose forming any new compound, on strong heating.
 
Actually there is no relation between the thermal stability and solubility of a substance. Solubility of a substance increases with increase in hydration energy, or decrease in lattice energy, whereas thermal stability depends upon the stability of the compound itself and the compound which it should form after decomposition.
 
If the compound which is should form after decomposition is less stable and does not want to exist in normal conditions, then the compound itself becomes thermally stable, and does not decompose.
 
If you consider the above example, which I gave, Lithium oxide is more stable than Lithium Carbonate, hence lithium carbonate decomposes easily to form lithium oxide and carbon dioxide. Whereas, in case of sodium carbonate, sodium oxide is somewhat less stable than sodium carbonate, due to which sodium carbonate does not decompose.
 
HOPE YOU GOT YOUR ANSWER...
THANKS!

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