The Kf for Cuen22 is much larger than the one for CuNH342 Th

The Kf for [Cu(en)2]^2+ is much larger than the one for [Cu(NH3)4]^2+. This difference is primarily an entropy effect. Explain why and calculate the difference between the delta S

Solution

We can set up the calculation as follows.
Cu2(aq) 4 NH3(aq) m888n8 Cu(NH3)4
2(aq) Kf 2.1 1013
Initial 0.10 M 1.0 M 0
Because there is no Cu(NH3)4 2 ion in the solution when we start, the initial value of Qf
for the reaction is zero and Qf is very much smaller than Kf for the reaction. Because Kf
for the complex is very large, essentially all of the Cu2 ions should form Cu(NH3)4
2 ions at equilibrium. We therefore define a set of intermediate conditions in which we shift the
reaction to the right until all of the Cu2 ion is converted into Cu(NH3)4 2 complex ions.

The value of Kf is so large that very little Cu(NH3)4 2 complex ion dissociates as the reaction
comes to equilibrium. It is therefore reasonable to assume that C is relatively small.

Even fairly dilute solutions of the OH ion have more than enough OH ion to precipitate Cu(OH)2 from a 0.10 MCu2 ion solution. As the amount of NH3 added to the solution increases, the concentration of the OH ion increases. But it doesn