Sample3 - Chem 6 Sample exam 3 (final) (200 points total) @...

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Chem 6 Sample exam 3 (final) (200 points total) @ This is a closed book exam to which the Honor Principle applies. @ The last three pages contain equations, physical constants, a periodic table and other good stuff; you can detach them for easy reference. @ Please write clearly and SHOW YOUR WORK. If you need to write on the back of the exam paper, please indicate this clearly. @ Some questions are more challenging than others. Allot your time accordingly, and try to answer EVERY question. @ Please put your name both on this page and on page 2. NAME: _________________________
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2 NAME: ____ ________ ________ FOR GRADING USE ONLY Question 1 (20 pts). ....................... __________ Question 2 (20 pts). ....................... __________ Question 3 (20 pts). ....................... __________ Question 4 (20 pts). ........................ __________ Question 5 (20 pts). ..................... __________ Question 6 (20 pts) . ....................... __________ Question 7 (20 pts) . ....................... __________ Question 8 (20 pts) . ....................... __________ Question 9 (20 pts) . ....................... __________ Question 10 (20 pts) . ....................... __________ TOTAL (200 pts) ...................... ===========
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3 1. (20 pts) The figure below represents part of the emission spectrum for a gas- phase hydrogen atom. All the lines result from electronic transitions from excited states to a state with unknown quantum number n . I have not shown all the lines in the spectrum between lines A and B, but line A has the shortest wavelength in the series, 3280 nm. Find the quantum number n and the wavelength for line B. Put your answers in the boxes below and show your work. AB wavelength n wavelength for line B
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4 where A* represents a molecule of A with enough energy to surmount the activation energy barrier. (a, 10 pts) Find the rate law for the production of B using the steady-state approximation for the intermediate A*. (b, 10 pts) In the gas phase, this reaction obeys first-order kinetics, but at very low pressures of A, second-order behavior is observed. Explain this observation in terms of your result from part (a) and give a physical interpretation of these observations in terms of the relative rates of the two steps. A B + C with the proposed mechanism 2. (20 pts) Consider the reaction A + A A* + A A* B + C k –1 k 1 k 2
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5 3. (20 pts, 10 each). The highest occupied molecular orbital (HOMO) for a molecule is the highest-energy MO which contains electrons. (a) Identify the HOMO of HF, and sketch the combination of atomic orbitals used to form this MO. [If the HOMO is actually a degenerate set of MO's, say so, and just sketch one of the set.] Your sketch should show the relative contributions of the atomic orbitals to the MO, where appropriate. Note: this should be a picture of the orbital, not the MO energy level scheme. (b) The ionization energy of a molecule can be defined in the same way as for an atom. The ionization energy of HF is i. greater than that of F ii. the same as that of F iii. less than that of F Circle your choice and explain your answer.
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6 4. (20 pts) (a, 4 pts) The atom connectivity for a molecule is shown below.
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This note was uploaded on 05/01/2008 for the course CHEM 5/6 taught by Professor Gribble during the Spring '08 term at Dartmouth.

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Sample3 - Chem 6 Sample exam 3 (final) (200 points total) @...

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