why sodium carbonate does not decompose on heating whereas zinc carbonate decomposes on heating?

Answer 1

In order for ANY chemical reaction to proceed spontaneously, there must be a negative change in the Gibb's Free Energy.
If the change in free energy is positive or zero, the reaction will not proceed on its own.

In the case of Na2CO3 or ZnCO3 decomposing on heating, without looking up the free energy values, one must simply assume that the free energy change for,
Na2CO3 --heat--> Na2O + CO2
is positive, and then free energy change for,
ZnCO3 --heat--> ZnO + CO2
is negative, under the conditions which the reaction is being attemped.

Answer 2

this is sodium carbonate you will might desire to apply electrolysis as a fashion to decompose it zinc and lead carbonate will decompose into their steel oxides and carbon dioxide whilst heated

Answer 3

we can start from the basic conception of heat stability of ionic compounds, it mainly depends on the lattice enthalpy(energy required to break 1 mole of a compound in positive and negative ions). for high lattice enthalpy in a compound it becomes hard to break the bonds between negative and positive ions.

Now amount of lattice enthalpy in the stated case will depend on the following factors of positive ion, as the negative ion is the same.
1)size of the ion
2)polarisation
3)electropositivity

1) Na+ in Na2CO3 is smaller that Zn2+ in ZnCO3,so the negatively charged ion can attract the positively charged nucleus in the centre of positive ion more powerfully in Na than Zn.

2) from fazans law we know existence of d-orbitals in (n-1) shell and high charge density accelerates the polarization in an ionic molecule.for Zn,we can find d-orbitals and higher charge density(+2 > +1|) than Na. so the molecule achieves a bit covalent properties which lessen its heat stabiltity.

3)from the sreies of electropositive elements, we find Na>>Zn in terms of reactivity and thus Na compounds are much more stable than those of Zn.also for greater electropositivity, Na is attarcted much by carbonate than Zn increasing its lattice enthalpy.

Thats why Na2CO3 is heat-stable but ZNCO3 is not.

Answer 4

sodium carbonate is thermally stable [in fact all 1A group carbonates are thermally stable] where as zinc carbonate is not