Answer
The equilibrium constant value for that reaction is equal to $0.0987$.
Work Step by Step
1. Write the equilibrium constant expression:
$K_{eq} = \frac{[Products]}{[Reactants]} = [NH_3][H_2S]$
** Notice: we do not consider the $NH_4HS$ concentration, because it is a solid.
2. Using the given values, calculate the $K_{eq}$:
$K_{eq} = 0.278 \times 0.355 = 0.0987$
