Chemistry of transition elements: compare question

Two copper(II) complexes are formed from the hexaaquacopper(II) ion in aqueous solution.

Complex A: $\ce{[Cu(H2O)6]^{2+} + 4NH3 -> [Cu(NH3)4(H2O)2]^{2+} + 4H2O}$

Complex B: $\ce{[Cu(H2O)6]^{2+} + 2en -> [Cu(en)2]^{2+} + 6H2O}$ (where en = 1,2-diaminoethane, a bidentate ligand)

Compare the stability constants, $K_\text{stab}$, for the formation of Complex A and Complex B. In your answer:

• write an expression for the $K_\text{stab}$ of $\ce{[Cu(en)2]^{2+}}$
• state which complex has the larger $K_\text{stab}$
• explain why this complex has a larger $K_\text{stab}$
• describe how the $K_\text{stab}$ values relate to the position of equilibrium in each ligand exchange.