For the reversible reaction,
\( \text{N}_2 (g) + 3\text{H}_2 (g) \rightleftharpoons 2\text{NH}_3 (g) \).
When the partial pressure is measured in atmosphere, the value of \( K_p \) at \( 500^\circ\text{C} \) is \( 1.44 \times 10^{-5} \).
The value of \( K_c \) when the concentration is expressed in \( \text{mol L}^{-1} \) is:
\(\underline{\hspace{3cm}}\).