Practice Final Exam - scrambled key (1).pdf

# L δ h rxn 2413 kjmol h 2 sg 2o 2 g so 3 g h 2 ol δ

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(l), Δ H rxn = -241.3 kJ/mol H 2 S(g) + 2O 2 (g) SO 3 (g) + H 2 O(l), Δ H rxn = -205.6 kJ/mol H 2 O(l) H 2 O(g), Δ H rxn = 41.9 kJ/mol What is the Δ H rxn of the overall balanced reaction? 1. 77.6 kJ/mol correct 2. 489 kJ/mol 3. -646 kJ/mol 4. 319 kJ/mol 5. -405 kJ/mol Explanation: The objective is to arrange the three reactions so that the sum of the reactions gives you the overall balanced chemical reaction. This is accomplished simply by reversing the first reaction and flipping the sign of that enthalpy of reaction. From there: Δ H rxn = - ( - 241 . 3) + ( - 205 . 6) + (41 . 9) = 77 . 6kJ / mol 038(part1of3)2.0points The molecule shown below is a rare alkaloid found in plants native to South America with profound cultural significance. F O N N H b c a What is the correct empirical formula for this compound? 1. C 13 H 12 FN 2 O 2. C 13 H 19 FN 2 O 3. C 15 H 17 FN 2 O 4. C 12 H 15 FN 2 O 5. C 13 H 19 N 2 O 6. C 13 H 17 FN 2 O correct Explanation: The empirical formula is C 13 H 17 FN 2 O. 039(part2of3)2.0points Which of the following best represents the bond angle labeled a ? 1. 109 . 5

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Version 001 Practice Final Exam 13 2. 178 3. 90 4. 104 . 5 correct 5. 120 6. 118 7. 180 Explanation: There are two (not shown) lone pairs on the O there which means there are 4 electron regions and therefore a tetrahedral electronic geometry which has a bond angle of 109.5 . The lone pairs are more repulsive than the bonding pairs and therefore pushes the angles down to about 104.5 . 040(part3of3)2.0points What is the electronic geometry around the central atom labeled b ? 1. Tetrahedral 2. Trigonal pyramid 3. Bent 4. Trigonal planar correct 5. Seesaw Explanation: In the line drawing, b has an understood hydrogen atom attached, giving the carbon a trigonal planar structure. The nitrogen labeled c has an understood lone pair, which gives it a tetrahedral electronic geometry. 041(part1of2)2.0points Use the following structure to answer the next two questions: H 2 N O OH How many sigma and pi bonds are in the organic structure above? 1. 12 σ and 2 π 2. 12 σ only 3. 10 σ and 2 π correct 4. 10 σ and 4 π 5. 8 σ and 2 π Explanation: Accounting for the ”understood” hydrogen atoms, there are a total of 8 single bonds and 2 double bonds. This is a total of 10 σ and 2 π . 042(part2of2)2.0points For the structure shown above, what is the hy- bridization around the carbonyl carbon (i.e. the carbon with the double bond to oxygen)? 1. sp 3 2. sp 3 d 3. sp 2 correct 4. sp 3 d 2 5. sp Explanation: The carbonyl carbon (i.e. the carbon with the double bond to oxygen) has three regions of electron density, corresponding to a sp 2 hybridization. 043 2.0points Consider a reaction that has a negative change in entropy and a negative change in enthalpy. Which of the following conditions will favor spontaneity?
Version 001 Practice Final Exam 14 1. This reaction is non-spontaneous at all temperatures 2. This reaction is spontaneous at all tem- peratures 3. Low Temperatures correct 4. High Temperatures Explanation: For this reaction, the spontaneity will be driven by the enthalpy term. This reaction will spontaneous only at low temperatures.
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• Winter '15
• bobby
• Energy, Chemical bond

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