Answer
$$K_c = 9.87 \times 10^{-2}$$
Work Step by Step
1. The exponent of each concentration is equal to its balance coefficient.
$$K_C = \frac{[Products]}{[Reactants]} = {[ NH_3 ][ H_2S ]}$$
Solid compounds do not appear in the expression.
2. Substitute the values and calculate the constant value:
$$K_C = ( 0.278 )( 0.355 ) = 9.87 \times 10^{-2}$$
