$2{\mathrm{NO}}_2\left(g\right)+7{\mathrm{H}}_2\left(g\right)\rightleftharpoons 2{\mathrm{NH}}_3\left(g\right)+4{\mathrm{H}}_2\mathrm{O}\left(l\right)$ 

What is the correct equilibrium expression for this reaction?

Consider the following reversible reaction:

 $cC+dD\Rightarrow aA+bB$

The reaction's equilibrium constant, measured in moles per liter of concentration:

$\Rightarrow K_c=\frac{\left[C{]}^c\right[D{]}^d}{\left[A{]}^a\right[B{]}^b}$

For the given reaction,

$2{\mathrm{NO}}_2\left(\mathrm{g}\right)+7{\mathrm{H}}_2\left(g\right)\rightleftharpoons 2{\mathrm{NH}}_3\left(g\right)+4{\mathrm{H}}_2\mathrm{O}\left(l\right)$

$K_C=\frac{{\left[{\mathrm{NH}}_3\right]}^2}{{\left[{\mathrm{NO}}_2\right]}^2{\left[{\mathrm{H}}_2\right]}^7}$

Where ${\mathrm{K}}_{\mathrm{c}}$ is the equilibrium constants of gaseous mixtures