Question

Which equiLiBrium constant expression(s) are for the following reaction NH₃(g) h3o (aq) ⇌ nh4 (aq) H₂O(l)?

1) Kc = [NH₄⁺][H₂O]/[NH₃][H₃O⁺]
2) Kc = [NH₃][H₃O⁺]/[NH₄⁺][H₂O]
3) Kc = [NH₄⁺][H₂O]
4) Kc = [NH₃][H₃O⁺]

Answer 1

The correct equilibrium constant expression for the ionization of NH₃ in water excludes the concentration of water and is represented as Kc = [NH₄⁺]/[NH₃][H₃O⁺]. Options including H₂O or with improper product/reactant placement are incorrect.

Step-by-step explanation:

When writing an equilibrium constant expression for a reaction, the concentrations of the products are placed in the numerator and the concentrations of the reactants in the denominator. For the reaction NH₃(g) + H₂O(l) ⇌ NH₄⁺ (aq) + OH⁻ (aq), the proper equilibrium constant expression, or the base ionization constant (Kₗ), would exclude the concentration of water (H₂O) because it is a pure liquid whose concentration remains constant and is typically omitted from the expression.

Therefore, the correct expression should only include the concentrations of the aqueous ions. The correct equilibrium constant expression for the ionization of NH₃ in water is:

Kc = [NH₄⁺]/[NH₃][H₃O⁺]

Option 3 that states Kc = [NH₄⁺][H₂O] is incorrect because it includes H₂O, and options 1 and 2 are incorrect as they both have the wrong placement of reactants and products relative to the actual reaction.