Question
For the equilibrium,
which of the following expressions is correct?
A.
$${K_p} = {p_{C{O_2}}}$$
B.
$${K_p} = \frac{{\left[ {MgO} \right]\left[ {C{O_2}} \right]}}{{\left[ {MgC{O_3}} \right]}}$$
C.
$${K_p} = \frac{{{p_{MgO}}.{p_{C{O_2}}}}}{{{p_{MgC{O_3}}}}}$$
D.
$${K_p} = \frac{{{p_{MgO}} + {p_{C{O_2}}}}}{{{p_{MgC{O_3}}}}}$$
Answer :
$${K_p} = {p_{C{O_2}}}$$
Solution :
In heterogeneous system, $${K_C}$$ and $${K_p}$$ are not depend upon the concentration or pressure of solid substance. Hence, at equilibrium their concentration or pressure are assumed as one.
$$\eqalign{
& MgC{O_3}\left( s \right) \rightleftharpoons MgO\left( s \right) + C{O_2}\left( g \right) \cr
& \therefore \,\,\,{K_p} = {p_{C{O_2}}} \cr} $$