Answer: The molecule methylamine (CH3NH2) can act as a

Chapter , Problem 98IE

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Problem 98 IE

The molecule methylamine (CH3NH2) can act as a monodentate ligand. The following are equilibrium reactions and the thermochemical data at 298 K for reactions of methylamine and en with Cd2+(aq):

Cd2+(aq) + 4 CH3NH2(aq) ⇌ [Cd(CH3NH2)4]2+(aq)

∆H° = -57.3 kJ; ∆S° = -67.3 J/K; ∆G° = -37.2 kJ

Cd2+(aq) + 2 en(aq) ⇌ [Cd(en)2]2+(aq)

∆H° = -56.5 kJ; ∆S° = +14.1 J/K; ∆G° = -60.7 kJ

(a) Calculate ∆G° and the equilibrium constant K for the following ligand exchange reaction

[Cd(CH3NH2)4]2+(aq) + 2 en(aq) ⇌ [Cd(en)2]2+(aq) + 4 CH3NH2(aq)

Based on the value of K in part (a), what would you conclude about this reaction? What concept is demonstrated? (b) Determine the magnitudes of the enthalpic (∆H°) and the entropic (-T∆S°) contributions to ∆G° for the ligand exchange reaction. Explain the relative magnitudes. (c) Based on information in this exercise and in the “A Closer Look” box on the chelate effect, predict the sign of ∆H° for the following hypothetical reaction:

[Cd(CH3NH2)4]2+(aq) + 4 NH3(aq) ⇌ [Cd(NH3)4]2+(aq) + 4 CH3NH2(aq)