I need a little help with a chemistry question and an explanation of the answer please

Question

Predict whether the equilibrium of the following reaction favors reactants or products: NH4+ + H2O ⇌ NH3 + H3O+

 

A) Reactants are favored. B) Products are favored. C) Neither side is favored.

Answer 1

This is determined quantitatively by analyzing the K_a or K_b of the reaction as written.  The reaction is written as the dissociation for ammonium ion.  Therefore the Ka for ammonium needs to be determined either from a table or from K_b for ammonia. The K_b for NH₃ is 1.8E-5.  K_a for NH₄⁺ is therefore 10E-14/1.8E-5.  

K_a for NH₄⁺ = 5.6 x 10^-10 . Since K_a for NH4+ is much less than 1, reactants are favored.

 

In a nonquantitative analysis, it is enough to know that NH₄⁺ is a weak acid and therefore does not dissociate much. Since it is a weak acid and does not dissociate much, reactants will be favored.