I would appreciate help on writing an equalibrium constant expression.

Explanation:
it would be
[tex]kc = (products) \div (reactants) \\ kc = \frac{nh3)^{2} \times (co2) \times (h2o)}{(nh4)^{2}co3 }[/tex]
this the expression however when you are working out Kc do not include nh4^2co3 as it is a solid and it's concentration remains constant so remember to remove the nh4^2co3 and usage would just have the top part to work out ok