# What does thermal stability of compounds depend on?

Does it somehow depend upon the lattice energy of the compound? My textbook says that Lithium carbonate is not so stable to heat and forms more stable $$\ce{Li2O}$$ and $$\ce{CO2}$$. Could it depend on the electropositive character? Because my textbook further sates that the stability of carbonates increases down the group.

The smaller the size of the ion, the higher the lattice energy and the greater the extent of the polarization. Li+ has a smaller size compared to $$\ce{Na+}$$, hence polarizes the $$\ce{CO3-}$$ ion at a greater extent compared to $$\ce{Na+}$$. $$\ce{Li2CO3}$$ therefore requires less energy to break while $$\ce{Na2CO3}$$ needs a higher energy making it more stable than $$\ce{Li2CO3}$$.