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  4. Which is least thermally stable?

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Q. Which is least thermally stable?

WBJEEWBJEE 2018The s-Block Elements

Solution:

$BeCO _{3}$ is least thermally stable. The thermal stability of carbonates increases down the group i.e from Be to $Ba$.

$\underset{(523 K)}{BeCO_3}<\, \underset{(813 K)}{MgCO_3}<\, \underset{(1173 K)}{CaCO_3}<\,\underset{(1562 K)}{SrCo_3}<\,\underset{(1633 K)}{BaCO_3}$

$BeCO _{3}$ is unstable to the extent that it is stable only in atmosphere of $CO _{2}$. These carbonates show reversible decomposition in closed container.

$MCO _{3} \rightleftharpoons MO + CO _{2}$

More stable the oxide is formed, lesser will be stability of carbonates