Why is `Li_(2)CO_(3)` decomposed at a lower temperature whereas `Na_(2)CO_(3)` at higher temperature?

Explanation

Lithium is less electropositive than sodium and therefore, carbonate of lithium is less stable than that of sodium. `Li_2CO_3` is not so stable to heat and therefore, decomposes at lower temperature. This is because lithium being very small in size polarises a large `CO_3^(2-)`ion leading to the formation of `Li_2 "and" CO_3` On the other hand, `Na_2CO_3` is very stable and decomposes at higher temperature.