Question

Consider the ionization of aqueous ammonia: NH3(aq) + H2O(l) ⇌ NH4 + (aq) + OH- (aq)

a)Using the thermodynamic data from the textbook (Appendix C), calculate the values of ∆H°rxn, ∆G°rxn, and ∆S°rxn for this process at 25o C.

b)Calculate the value of Kb (with 2 sig figs) at 25o C from the value of ∆G°rxn.

c) The value of ∆G°rxn you obtain (if your calculations are correct) must be positive, indicating that the reaction in question is non-spontaneous. Why does the ionization of ammonia actually occur in its aqueous solution?

d)Of the three thermodynamic values (∆H°rxn, ∆G°rxn, and ∆S°rxn), which are going to be fairly independent of temperature, and which are going to change significantly with changing T?

e) Estimate the values of ∆H°rxn, ∆G°rxn, ∆S°rxn, and Kb at 0o C.

f) Estimate the temperature at which Kb = 2.1 × 10-5 .

Answer 1

c) Ammonia is a Neonates base which can take proton to produce ammonium ion. Non aqueous solution can't give the proton but water can give the proton. Hence Ammonia can ionize in aqueous solutions only.

d) Delta H^° and Delta S^0 are independent of temperature.