
Arrange the following alkali metal carbonates in increasing order of their thermal stability:
\[{\mathbf{L}}{{\mathbf{i}}_{\mathbf{2}}}{\mathbf{C}}{{\mathbf{O}}_{\mathbf{3}}},{\mathbf{R}}{{\mathbf{b}}_
{\mathbf{2}}}{\mathbf{C}}{{\mathbf{O}}_{\mathbf{3}}},{\mathbf{C}}{{\mathbf{s}}_{{\mathbf{2}}}}{\mathbf{C}}{
{\mathbf{O}}_{\mathbf{3}}},{\mathbf{N}}{{\mathbf{a}}_{\mathbf{2}}}{\mathbf{C}}{{\mathbf{O}}_{\mathbf{3}}},
{{\mathbf{K}}_{\mathbf{2}}}{\mathbf{C}}{{\mathbf{O}}_{\mathbf{3}}}\]
A. \[\;\;L{i_2}C{O_3} < N{a_2}C{O_3} < {K_2}C{O_3} < R{b_2}C{O_3} < C{s_2}C{O_3}\]
B. \[C{s_2}C{O_3} < N{a_2}C{O_3} < {K_2}C{O_3} < R{b_2}C{O_3} < L{i_2}C{O_3}\]
C. \[\;L{i_2}C{O_3} < {K_2}C{O_3} < N{a_2}C{O_3} < R{b_2}C{O_3} < C{s_2}C{O_3}\]
D. None of these
Answer
516.3k+ views
Hint:Thermal Stability – It can be defined as the ability of the bonded molecules to resist the action of heat and maintain its properties. Or in other words, we can say the maximum temperature to which a molecule is heated by which it does not lose its properties.
Complete step by step answer:
Now we will discuss about the factors describing about the thermal stability of metal carbonates in order
to find the order.
The Reason behind the increasing and decreasing Thermal stabilities are given below
Size – The thermal stability usually depends on the size of the element and increases down the group. As
we move from lithium to cesium, the thermal stability increases due to increase in size. The more the size,
the more heat required to decompose the compound.
Charge density – The charge density is inversely proportional to the size of the positive ion. Due to this,
the effect on carbonate ion increases. Now as the positive ion increases down the group, the charge
density decreases by which the effect on carbonate ion decreases and hence increasing the thermal
stability of compound.
Structure - The structure of the substance heavily affects the thermal stability of the substance and the
structure is dependent on the bonds between atoms that hold that structure together.
Charges are delocalized – The structure of \[C{O_3}\]has two single carbon-oxygen bonds and one double
bond. The two oxygen atoms have a negative charge on both of them. In Carbonate ion, the charges are
distributed in the whole ion, with greater concentrated density on oxygen atoms. We can also say, the
charges are delocalized.
Thus, the correct option is A, \[\;{\mathbf{LiC}}{{\mathbf{O}}_{\mathbf{3}}} <
{\mathbf{N}}{{\mathbf{a}}_{\mathbf{2}}}{\mathbf{C}}{{\mathbf{O}}_{\mathbf{3}}} <
{{\mathbf{K}}_{\mathbf{2}}}{\mathbf{C}}{{\mathbf{O}}_{\mathbf{3}}} <
{\mathbf{R}}{{\mathbf{b}}_{\mathbf{2}}}{\mathbf{C}}{{\mathbf{O}}_{\mathbf{3}}} <
{\mathbf{C}}{{\mathbf{s}}_{\mathbf{2}}}{\mathbf{C}}{{\mathbf{O}}_{\mathbf{3}}}\]
Since with increase in atomic number the stability increases.
Note:
The Thermal Stability increases with the increase in atomic size and the atom with greater size tends
to decompose less likely than the atom with smaller size at a same temperature so their stability
increases with the increasing size.
Complete step by step answer:
Now we will discuss about the factors describing about the thermal stability of metal carbonates in order
to find the order.
The Reason behind the increasing and decreasing Thermal stabilities are given below
Size – The thermal stability usually depends on the size of the element and increases down the group. As
we move from lithium to cesium, the thermal stability increases due to increase in size. The more the size,
the more heat required to decompose the compound.
Charge density – The charge density is inversely proportional to the size of the positive ion. Due to this,
the effect on carbonate ion increases. Now as the positive ion increases down the group, the charge
density decreases by which the effect on carbonate ion decreases and hence increasing the thermal
stability of compound.
Structure - The structure of the substance heavily affects the thermal stability of the substance and the
structure is dependent on the bonds between atoms that hold that structure together.
Charges are delocalized – The structure of \[C{O_3}\]has two single carbon-oxygen bonds and one double
bond. The two oxygen atoms have a negative charge on both of them. In Carbonate ion, the charges are
distributed in the whole ion, with greater concentrated density on oxygen atoms. We can also say, the
charges are delocalized.
Thus, the correct option is A, \[\;{\mathbf{LiC}}{{\mathbf{O}}_{\mathbf{3}}} <
{\mathbf{N}}{{\mathbf{a}}_{\mathbf{2}}}{\mathbf{C}}{{\mathbf{O}}_{\mathbf{3}}} <
{{\mathbf{K}}_{\mathbf{2}}}{\mathbf{C}}{{\mathbf{O}}_{\mathbf{3}}} <
{\mathbf{R}}{{\mathbf{b}}_{\mathbf{2}}}{\mathbf{C}}{{\mathbf{O}}_{\mathbf{3}}} <
{\mathbf{C}}{{\mathbf{s}}_{\mathbf{2}}}{\mathbf{C}}{{\mathbf{O}}_{\mathbf{3}}}\]
Since with increase in atomic number the stability increases.
Note:
The Thermal Stability increases with the increase in atomic size and the atom with greater size tends
to decompose less likely than the atom with smaller size at a same temperature so their stability
increases with the increasing size.
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