Chemistry Exam: Thermodynamics, Lewis Acidity, and Reactions, Exams of Inorganic Chemistry

Download Chemistry Exam: Thermodynamics, Lewis Acidity, and Reactions and more Exams Inorganic Chemistry in PDF only on Docsity! Name:_____________________________ CHEM 3111/6170 Third Exam 15 October 2004 In taking this examination, you are expected to adhere to the GT academic honor code. At a minimum this requires that you utilize only the materials supplied to you (except for a non-programmable calculator), and that you do not give help to, or accept help from, others. 1. The following thermodynamic data were reported for coordination of K+ to 18-crown-6 and pentaglyme, respectively: O O O OO O 18-crown-6 O O O OO O pentaglyme logK 6.06 2.10 ΔH –56.0 kJmol–1 –36.4 kJmol–1 ΔS –71 JK–1mol–1 –84 JK–1mol–1 a) (5 points) Although pentaglyme has the same number of coordinating oxygen atoms, its affinity for K+ is lower by 4 orders of magnitude compared to 18-crown-6. Explain briefly (use the given thermodynamic data to support your argument). b) (5 points) The entropy change ΔS is negative for both coordination equilibria. Is this observation within your expectation or would you have predicted a positive entropy change? Comment briefly. c) (5 points) Compared to 18-crown-6 do you expect the sulfur-analogue shown below to form a more or less stable complex with K+? Explain briefly. S S S SS S 2. (15 points) Arrange the following species in order of increasing Lewis acidity: a) BCl3, PCl3, AlCl3 b) PF5, AsF5, ClF5 c) Explain briefly why BF3 is less Lewis-acidic than BBr3, whereas SnF4 is stronger Lewis-acidic than SnCl4.