Question

NH₄HS(s) ⇌ NH₃(g) + H₂S(g) at a certain temperature, Kc=8.5×10⁻³. A reaction mixture at this temperature containing solid NH₄HS has [NH₃]=0.145M and [H₂S]=0.145M.

Options:
A. NH₄HS dissociation is favored.
B. NH₄HS dissociation is not favored.
C. The reaction has reached equilibrium.
D. Kc is greater than the initial concentrations.

Answer 1

The reaction quotient Q, calculated from the concentrations of NH₃ and H₂S, is greater than Kc, indicating that NH₄HS dissociation is not favored and the reaction will shift to form more NH₄HS to reach equilibrium.

Step-by-step explanation:

The subject of the student's question involves chemical equilibrium, specifically involving the compound NH₄HS and its dissociation into NH₃ and H₂S. To determine whether NH₄HS dissociation is favored, not favored, or if the reaction has reached equilibrium, we utilize the equilibrium constant Kc and compare it with the reaction quotient Q, which is calculated from the given concentrations of NH₃ and H₂S.

As NH₄HS is a solid, it does not appear in the equilibrium constant expression. The equilibrium constant expression for the given reaction is Kc = [NH₃][H₂S]. Given that Kc = 8.5×10⁻³ and that the concentrations of NH₃ and H₂S are both 0.145M, we can calculate the reaction quotient Q = [NH₃][H₂S] = (0.145)(0.145).

Upon calculation, Q = 0.021025 which is greater than Kc = 8.5×10⁻³. Since Q > Kc, the dissociation of NH₄HS is not favored, and the system will shift to form more solid NH₄HS to reach equilibrium.