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Equilibrium constant $K_p$ for following reaction : $MgCO_3(s) \rightleftharpoons MgO(s) + CO_2(g)$
A
$K_p = P_{CO_2}$
B
$K_p = P_{CO_2} \times \dfrac{P_{CO_2} \times P_{MgO}}{P_{MgCO_3}}$
C
$K_p = \dfrac{P_{CO_2} + P_{MgO}}{P_{MgCO_3}}$
D
$K_p = \dfrac{P_{MgCO_3}}{P_{CO_2} \times P_{MgO}}$
Detailed Solution
For a heterogeneous equilibrium, pure solids (and pure liquids) have constant activity (taken as 1), so they are not included in the equilibrium expression.
Here $MgCO_3$ and MgO are solids, so only $CO_2$ appears:
$K_p = P_{CO_2}$
Here $MgCO_3$ and MgO are solids, so only $CO_2$ appears:
$K_p = P_{CO_2}$