Question

on heating LiCO3 it dissociate in LiO2 + CO2 as on heating Na2CO3 it dont dissociate why??

Answer 1

This is Fajan's rule.
As size of cation is less there is more polarization in the molecule and hence Most Lithium compounds are covalent. Thus unstable to heat.
But Na2CO3 is predominantly ionic and hence it is stable to heat.