Question

Among the following compound, the thermal stability is least in:

• A. $K_{2}C{O}_3$
• B. ${Na}_{2}C{O}_3$
• C. $BaC{O}_3$
• D. ${Li}_{2}C{O}_3$

Answer 1

The correct option is D ${Li}_{2}C{O}_3$

Lithium carbonate $L{i}_{2}C{O}_3$ is least thermally stable.
Replacement of the larger carbonate ion by a smaller oxide ion leads to increased lattice energy thus favors decomposition. Also, strong polarizing action of small $L{i}^{+}$ ion distorts the electron cloud on the nearby oxygen atom of the large carbonate ion to such an extent that the C-O bond gets weakened and Li-O bond becomes stronger which ultimately leads to the decomposition of carbonate to oxide and carbon dioxide.
$L{i}_{2}C{O}_3\stackrel{\Delta }{\to }L{i}_{2}O+C{O}_2$