Question

Which of the following cannot decompose on heating to give $\text{C}{{\text{O}}_{2}}$?
A.$\text{L}{{\text{i}}_{2}}\text{C}{{\text{O}}_{3}}$
B.$\text{N}{{\text{a}}_{2}}\text{C}{{\text{O}}_{3}}$
C.$\text{KHC}{{\text{O}}_{3}}$
D.$\text{BaC}{{\text{O}}_{3}}$

Answer 1

Hint:The breaking down of the compounds into two or more products is known as decomposition and when it happens due to heating then the process is known as Thermal Decomposition. Sodium carbonate is quite stable as compared to the other compounds due to which it does not get decomposed on heating. A very high temperature is required to do the same.

Complete answer:
Lithium carbonate decomposes on heating into lithium oxide and carbon dioxide. Both lithium and sodium are alkali metals but as we move down the alkali group, the electropositive nature of the metal increases due to which it becomes more stable. Electropositive nature is the tendency to lose electrons to form positive ions. This is done to acquire stable noble gas configuration as alkali metals have only one electron in orbital of their s- subshell. Lithium being smaller in size has high charge density due to which it polarizes the carbonate ion and leads to the formation of lithium oxide which is more stable and carbon dioxide.
$L{{i}_{2}}C{{O}_{3}}\xrightarrow{\Delta }L{{i}_{2}}O+C{{O}_{2}}$
Potassium bicarbonate $KHC{{O}_{3}}$ also decomposes to potassium carbonate, carbon dioxide and water at temperature of around${{120}^{0}}C$.
$2KHC{{O}_{3}}\xrightarrow{\Delta }{{K}_{2}}C{{O}_{3}}+C{{O}_{2}}+{{H}_{2}}O$
Barium carbonate decomposes into barium oxide and carbon dioxide on heating.
$BaC{{O}_{3}}(solid)\xrightarrow{\Delta }BaO(solid)+C{{O}_{2}}(gas)$
Sodium carbonate has high lattice enthalpy which is the energy required to break I mole of a compound in positive and negative ions. The electropositive nature of sodium ion makes it to get much attracted by carbonate ion which increases its lattice enthalpy thereby providing stability to it.

Hence, the correct choice is (B).
Note:
Sodium acquires a high position in metal reactivity series so it forms a very strong and stable bond with carbonate ion due to which it resists decomposition by normal heating because a lot of energy is required to decompose it completely. Reactivity series is metal series which gives the metals in decreasing order of their reactivity. Sodium acquires second position in this series which contributes to its stability.