General Chemistry II Final Exam (100 pts) Spring 2013 Name _______________________________ This exam is closed-­‐book, closed notes, and is for you alone to complete. You may use a calculator and a periodic table. You may take no more than three hours to complete the exam. The exam is due by 12:00 noon on Monday May 13. Please bring the completed exam to my office. Thanks. Please answer ALL of the questions in both sections Short Answer (2 pts each) 1. Using the data in the table below, indicate which bond is the lowest
potential energy arrangement.
Bond
C-O
Average bond
energy, kJ/mole
358
C=O
745
C≡O
1070
Concentration
2. Consider the following reaction, and indicate which curve in the graph graph represents product (B), and which represents reactant (A) after the reaction has proceeded for some time: A(g)  B(g). Time
3. Which of the following compounds will be optically active? 1
4. Which of the following statements describes the correct method of preparation of 1.00 L of a 2.0 M urea solution? urea= 60.06 g/mol A. Dissolve 120 g of urea in 1.00 kg of distilled water. B. Dissolve 120 g of urea in 880 g of distilled water. C. Dissolve 120 g of urea in enough distilled water to produce 1.00 L of solution. D. Dissolve 120 g of urea in 1.00 liter of distilled water. E. The density of urea is needed in order to do this calculation. 5. For the following reaction, what is the reaction rate in terms of each reactant & product? 2N2O5(g)  4NO2(g) + O2(g) 6. Give the condensed electron configuration and partial (valance) orbital diagram for Br. 7. Write complete Lewis dot structures for the following molecules, and indicate ideal bond angles for each: a. AlCl3 b. CF4 c. SF6 8. What is the hybridization of each carbon in C2H2? 2
Long Answer (7 pts each) 1. The compound RX3 decomposes according to the equation: 3RX3 → R + R2X3 + 3X2 In an experiment the following data were [RX3](mol L-­‐1) collected for the decomposition at 100°C. What is t(s) 0 0.85 the average rate of reaction over the entire 2 0.67 experiment? 6 0.41 8 0.33 12 0.20 14 0.16 2. Hydrogenation of double and triple bonds is used to prevent unsaturated oils from oxidizing. Another application of hydrogenation is the conversion of acetylene to ethane. Calculate (in kJ) the standard enthalpy change (ΔH°) for the hydrogenation of ethyne (acetylene) to ethane. → H-­‐C≡C-­‐H(g) + 2H2(g) H3C-­‐CH3(g) Bond: C-­‐C C≡C C-­‐H H-­‐H Bond energy 347 839 413 432 (kJ/mol): 3
3. In class we repeated the assertion that there is “no temperature change during a phase change.” Imagine an uncovered pot of water being heated on a stove. Why is there no temperature change (i.e., why isn’t the water in the pot getting hotter) even as we continue to apply thermal energy to the system (heating the pot of water)? 4. How does the following figure help illustrate why a chemical reaction will form more product at a higher temperature? Number of molecules
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5. If you have one liter of a 0.5 M aqueous solution of MgCl2, how many ions will there be in that one liter of solution? 6. Which of the following two molecules will have a lower boiling point, and why? B
A
H2
C
H 3C
H2
C
OH
C
H2
HO
OH
C
H2
5
7. Potassium fluoride, KF, is used for creating “frosted” glass. Calculate the molarity of a solution prepared by dissolving 78.6 g of KF in enough water to produce 225 mL of solution. 8. Identify the two principal products of the reaction between ammonia and ethyl propionate. Will the products be pair a, or pair b?. What electron arrangements in the propionate and ammonia promote this reaction? (hint: where appropriate, add lone pairs to the structures below) Propionate ammonia 6
9. For the reaction: 3A(g) + 2B(g) → 2C(g) + 2D(g) the following data was collected at constant temperature. Determine the correct rate law for this reaction. Trial Initial [A] Initial [B] Initial Rate (mol/L) (mol/L) (mol/(L·min)
) 1 0.200 0.100 6.00 × 10-­‐2 2 0.100 0.100 1.50 × 10-­‐2 3 0.200 0.200 1.20 × 10-­‐1 4 0.300 0.200 2.70 × 10-­‐1 7
10. When a fuel is oxidized in a combustion reaction, for example the combustion of propane in a camping stove, where does the energy come from that is providing the heat for cooking food? 8
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Crossword. 0.5 point for each correct answer (14 pts). 10
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