Question

Aqueous solutions of ammonia (NH3) and hydrogen cyanide (HCN) react to produce ammonium cyanide, (NH4CN) according to the following equilibrium reaction. NH3(aq) + HCN(aq) = NH4+ (aq) + CN (aq) Given the following equilibrium constants, which statement best describes the reaction once equilibrium is established? (Kw - 1.01 x 10-14) NH4+ Ka = 5.6 x 10-10 HCN ka = 4.0 x 10-10 reaction is product favored, K<1 reaction is neither reactant nor product favored reaction is product favored, K>1 reaction is reactant favors, K> 1 reaction is reactant favors, K<1

Answer 1

Reaction 1:

HCN ------> H⁺ + CN^- ---------(1)--------------- Ka1 = 4 x 10^-10

Reaction 2:

NH₄⁺------> H⁺ + NH₃ ---------(2)--------------- Ka2 = 5.6 x 10^-10

Net reaction is:

HCN + NH₃ <==========> NH₄⁺ + CN^- ------------------- K = ?

• Net reaction = reaction (1) + reversed reaction 2

Therefore, K = K_a1 x (1/K_a2)

K = (4 x 10^-10) x (1/5.6 x 10^-10)

∴ K = 0.7143

• So the correct option is : reaction is reactant favored, K < 1