Answer
a. $$K_c = \frac{[ N_2 ][ H_2 ]^{ 3 }}{[ NH_3 ]^{ 2 }}$$
b. $K_c = 9.4$
Work Step by Step
1. Write the equilibrium constant expression:
$$K_c = \frac{[Products]}{[Reactants]} = \frac{[ N_2 ][ H_2 ]^{ 3 }}{[ NH_3 ]^{ 2 }}$$
2. Substitute the values and calculate the constant value:
$$K_c = \frac{( 3.0 )( 0.50 )^{ 3 }}{( 0.20 )^{ 2 }} = 9.4$$
