chm exam 3 fall07 key

chm exam 3 fall07 key - CHM 2045 Exam 3 (Form Code A)...

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1 CHM 2045 Exam 3 (Form Code A) November 15, 2007 Instructions: On your scantron sheet enter your name, UF ID number (start on the first space and leave the last space blank), Discussion Section No. and Form Code (see above). This exam consists of 25 multiple choice questions each worth 10.0 points for a total maximum of 250 pts. Keep your exam sheet (mark your answers on it and the scantron sheet). Turn in only the scantron. Any bubbling error will count as an incorrect response . Possibly Useful Info : h = 6.626x10 -34 J·s; R = 0.0821 L•atm/mol•K; R = 8.3145 J/ mol•K 1. How many σ bonds and π bonds are in acetonitrile, CH 3 CN? (1) 3 σ + 2 π (2) 4 σ + 2 π (3) 4 σ + 3 π (4) 5 σ + 1 π (5) 5 σ + 2 π 2. Molecular Orbital (MO) Theory treats a molecule as a collection of atomic nuclei with electron orbitals that are (a) ______ over the entire molecule, thereby eliminating the need for (b) _______ to depict molecules with fractional bond orders. (Correctly fill in the blanks with choices from below.) (1) (a) = localized, (b) = resonance structures (2) (a) = delocalized, (b) = atomic structures (3) (a) = localized, (b) = free-radical structures (4) (a) = delocalized, (b) = resonance structures (5) (a) = delocalized, (b) = nonbonding structures 3. An evacuated 1.00 L gas bulb was filled at STP (standard temperature and pressure) with 1.34 g of an unknown hydrocarbon (compound of carbon and hydrogen), which was then burned in excess oxygen, completely converting it to carbon dioxide and 2.41 g water. What is the molecular formula of the hydrocarbon? (1) CH 3 (2) C 2 H 6 (3) C 2 H 2 (4) C 3 H 4 (5) C 3 H 8 4. A sample of solid ammonium sulfide (NH 4 ) 2 S, is placed in a closed bulb which is then filled with 0.0150 mol of inert He gas. The pressure of the He at 25°C is 145 mm Hg. The bulb is then heated to 325°C and all of the (NH 4 ) 2 S decomposes to form gaseous NH 3 and H 2 S, with a resulting total gas pressure in the bulb of 875 mm Hg. What is the partial pressure of the NH 3 gas in the bulb at 325°C? (Assume that the volume of the
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chm exam 3 fall07 key - CHM 2045 Exam 3 (Form Code A)...

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