Thermal Stability of Carbonates and Nitrates

Carbonate Thermal Stability

Group 1 Carbonates:

$Li_{2}CO_{3}$ decomposes on heating: $Li_2CO_3 \xrightarrow{\Delta} Li_2O + CO_2\uparrow$
$Na_{2}CO_{3}$ , $K_{2}CO_{3}$ , $Rb_{2}CO_{3}$ , $Cs_{2}CO_{3}$ are thermally stable (no decomposition at normal temperatures)

Group 2 Carbonates:

All decompose on heating: $MCO_3 \xrightarrow{\Delta} MO + CO_2\uparrow$
Thermal stability ↑ down Group 2: $BeCO_{3}$ < $MgCO_{3}$ < $CaCO_{3}$ < $SrCO_{3}$ < $BaCO_{3}$

Nitrate Thermal Decomposition

Metal	Nitrate decomposition	Products
Li	$4LiNO_3 \rightarrow 2Li_2O + 4NO_2 + O_2$	Oxide, $NO_{2}$ , $O_{2}$ (like Mg)
Na, K, Rb, Cs	$2MNO_3 \rightarrow 2MNO_2 + O_2$	Nitrite + $O_{2}$
Be, Mg	$2M(NO_3)_2 \rightarrow 2MO + 4NO_2 + O_2$	Oxide, $NO_{2}$ , $O_{2}$
Ca, Sr, Ba	$2M(NO_3)_2 \rightarrow 2MO + 4NO_2 + O_2$	Oxide, $NO_{2}$ , $O_{2}$

Pattern: Li and all Group 2 nitrates → oxide + $NO_{2}$ + $O_{2}$ (extensive decomposition) Na and other heavy alkali metals → nitrite + $O_{2}$ (less extensive)

Reason: $Li^{+}$ (high polarizing power) acts like $Mg^{2+}$ — both destabilize the nitrate more completely.