[Kemiaa]

Hi
I read that "you can compare stabilities of compounds if you know their enthalpies of formation. But that's only allowed if they have at least one common reactant." Can someone help me to understand this? Why they need to have one common reactant? Why not all reactants should be same?
Thanks for *delete me*!

[Enthalpy]

I don't understand it neither, sorry.

By the way, "stability" is often understood as "strong negative heat of formation", but then it shouldn't be confused with the risk of detonation, the sensitivity to shocks, and so on.