177Exam3KeySS07

177Exam3KeySS07 - Prof Joe Burnett Summer 2007 This exam...

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Unformatted text preview: Prof. Joe Burnett Summer 2007 This exam consists of 29 questions on 10 pages. CHEM 177 Hour Exam III July 5, 2007 Name______________________ Recitation Instructor Circle one: Cherry Gloria GRADING PAGES Page 2 Page 3 Page 4 Page 5 Page 6 Page 7 Page 8 TOTAL POINTS 14 pts 18 pts 18 pts 8 pts 20 pts 16 pts 10 pts 104 pts SCORE ________ ________ ________ ________ ________ ________ ________ Note: The method that you use in solving questions must be clearly shown to receive full credit. Questions are written on both sides of each page. A periodic table, solubility rules, and other important information is on the last page of the exam. This may be removed and used for scratch paper and reference. Do not put answers on the data page – it will not be graded. Answer Key 2 1. (2 pts) Which of the following is expected to react most vigorously with magnesium metal? A. I 2 B. Cl 2 C. Br 2 D. Ca E. S 8 2. Complete and balance the following molecular reaction equations. For full credit, include phase of all products. A. (3 pts) MgO (s) + 2 HNO 3 (aq) ⎯→ ⎯ Mg(NO 3 ) 2 (aq) + H 2 O ( l ) B. (3 pts) 2 K (s) + 2 H 2 O ( l ) ⎯→ ⎯ H 2 (g) + 2 KOH (aq) 3. (6 pts) Estimate Δ H for the following gas-phase reaction. For full credit, show all work and report your answer to the correct number of significant figures. ⎯→ ⎯ Δ H rxn ≈ Σ i D(Bonds Broken) – Σ j D(Bonds Formed) ≈ 5 D(C–H) + D(C–C) + D(C–O) + D(O–H) – 6 D(C–H) – 2 D(C–O) (optional step) ≈ 5 D(C – H) + D(C–C) + D(C – O) + D(O–H) – D(C–H) – D(C–O) (optional step) ≈ D(C–C) + D(O–H) – D(C–O) – D(C–H) ≈ 348 kJ + 463 kJ – 358 kJ – 413 kJ = +40. kJ (2 sig figs) C C H H H H H O H H C O C H H H H H 3 4. (6 pts) Determine the best Lewis structure for N 2 O. Clearly and completely but briefly explain your answer. formal charge: –1 +1 0 0 +1 –1 –2 +1 +1 1. Determine the formal charge on each atom in each structure. 2. The best structure minimizes deviation from 0 AND puts the negative charge on the more electronegative atom. 3. The middle structure is best; O is more electronegative....
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This note was uploaded on 03/26/2008 for the course CHEM 177 taught by Professor Greenbowe during the Summer '06 term at Iowa State.

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177Exam3KeySS07 - Prof Joe Burnett Summer 2007 This exam...

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