Question

Why is $Li_{2}CO_{3}$ decomposed at a lower temperature whereas $Na_{2}CO_{3}$ at higher temperature ?

Answer 1

The decomposition of any carbonate salt depends upon the ease with which the base can attract $CO_2$ and the stability of the salt.

In general, if the base is a strong one it attracts the acidic $CO_2$ very easily whereas the weak base cannot attract the acidic oxide that easily.

Thus, NaOH attracts $CO_2$ forming more stable salt.

More stable the salt, more is the energy needed for its decomposition. This accounts for the fact that $Na_2CO_3$ decomposes at a higher temperature. If we take the case of $Li_2CO_3$, it is a product of the weak base LiOH and weak acidic acid.

Since, weak acid cannot attract $CO_2$ easily. As such the salt formed is not stable.

Thus, it decomposes at a lower temperature indicating that less energy is enough for its decomposition to lithium oxide and carbon dioxide.

Further the small size of the lithium ion facilitates the polarisation of electron cloud of the oxygen atom to which it is attached. Thus, Li-O bond becomes stronger and C-O bond becomes weaker. Thus lithium carbonate decomposes as - $Li_2CO_3 \rightarrow Li_2O+CO_2$

Answer 2

The decomposition of any carbonate salt depends upon the ease with which the base can attract CO_2CO2​ and the stability of the salt.

In general, if the base is a strong one it attracts the acidic CO_2CO2​ very easily whereas the weak base cannot attract the acidic oxide that easily.

Thus, NaOH attracts CO_2CO2​ forming more stable salt.

More stable the salt, more is the energy needed for its decomposition. This accounts for the fact that Na_2CO_3Na2​CO3​decomposes at a higher temperature. If we take the case of Li_2CO_3Li2​CO3​ , it is a product of the weak base LiOH and weak acidic acid.

Since, weak acid cannot attract CO_2CO2​ easily. As such the salt formed is not stable.

Thus, it decomposes at a lower temperature indicating that less energy is enough for its decomposition to lithium oxide and carbon dioxide.

Further the small size of the lithium ion facilitates the polarisation of electron cloud of the oxygen atom to which it is attached. Thus, Li-O bond becomes stronger and C-O bond becomes weaker. Thus lithium carbonate decomposes as - Li_2CO_3 \rightarrow Li_2O+CO_2Li2​CO3​→Li2​O+CO2​