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Ex-2-3530-S11-soln (2)

Ex-2-3530-S11-soln (2) - CHEM 3530 Exam 2 March 4 2011...

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Unformatted text preview: CHEM 3530 - Exam 2 - March 4, 2011 Constants and Conversion Factors NA = 6.02x1o23 mor1 R = 8.31 J/mol-K = 8.31 kPa-L/mol-K 1 bar = 100 kPa 1 kPa = 7.50 torr r 1 J = 1 kPa—L 1 kcal = 4.184 kJ Molar Masses C8H18 - 114. C4H1o - 58 CHEM 3530 - Exam 2 — March 4, 2011 f Name gfl’é‘h"! (69) PART I. MULTIPLE CHOICE (Circle the ONE correct answer) 1. For the combustion reaction, C3Ha(gas) + 3 02(gas) —+ 3 COz(gas) + 4 H20(liq) at 25 °C, the internal energy change is AU = -2220 kJ. What is AH for this reaction? (A) —2215 kJ (B) 222.5 k (C) -2220 RJ (D) 2217.5 kJ 2. The enthalpy of vaporization of octane, C8H1a, is 41.6 kJ/mol. What is the heat involved when 65 grams of octane are condensed from the gas to the liquid phase at 1 bar pressure and 125 °C? (A) +23.7 kJ (B) -73.0 N (D) Cannot be determined without the constant pressure molar eat capacity. 3. The enthalpy change for the reaction, 8(3) + 3/2 02(9) —> 803(9), is -395 kJ. Therefore, the enthalpy change for the reaction, 3 803(9) -+ 3 8(3) + 9/2 02(9), is (B) +790 kJ (C) +132 kJ (D) -1185 kJ 4. For the reaction 2 NO(g) + 02(9) —> 2 N02(g), AH = -114.2 kJ. The Enthalpy of Formation of N02(g) is +33.2 kJ/mol. Therefore, the enthalpy of formation of NO(g) is (A) -23.9 kJ/mol B) +90.3 kJ/mo (C) +23.9 kJ/mol (D) -90.3 kJ/mol 5. The Fuel Value (aka Specific Enthalpy) of butane, C4H1o, is 50. kJ/g. Therefore, the enthalpy of combustion of butane is ' (A) 0.90 kJ/mol (B) +2900 kJ/mol (C) -2900 kJ/mol (D) -690 kJ/mol 6. The enthalpy of formation of liquid trichloromethane, CHCl3(l) is -103. kJ/mol. Which of the following equations islare correct: ya) 2 02(9) + 2 C(gr) + 2 HCl(g) —> 2 CHCI3(I) AH = -206 kJ ./(ii) 2 CHCI3(I) —> H2(g) + 3 012(9) + 2 C(gr) AH = +206 kJ Xaii) (1/2) H2(g) + 3 C(gr) + 3 Cl(g) —) CHCI3(I) AH = -103 kJ (A) ionly (B) iii only (C) ii&iii 7. The standard molar‘entropies of 8(3), 02(9) and 303(9) are 32 J/mol—K, 205 J/mol—K, and 257 J/mol—K, respectively. Therefore, the entropy Change for the reaction 2 S(s) + 3 02(9) —) 2 803(9) is (A) +450 J/K (B) +165 J/K . (C) -118J/K 8. The constant volume molar heat capacity of C02(g) is 28.8 J/mol-K. What is AS when 5 moles of 002(9) is heated at constant volume from 100 °C to 400 °C? (A) +820 J/K (B) +200 J/K (D) +17 J/K 9. When two moles of N2(g) at 25 °C and 50 L are compressed reversibly and isotherrnally to a final volume of 20 L, the entropy change is (A) -75 J/K (B) +152 J/K (C) 4.5 kJ/K 10. When a gas is compressed adiabatically and reversibly, then: ) AU>0 & AS=O (B) AU<0 & AS=O (C) AU<0 & AS>O (D) AU>0 & AS<O 11. The normal boiling point of methanol is 64 °C. The Enthalpy of Vaporization of methanol is 35.3 kJ/jmol. What is the entropy change of the surroundings when 1 mole of methanol gas is condensed reversibly to the liquid at 64 °C? (A) -550 J/K (B) +550 J/K (D) -105 J/K 12. The enthalpy of fusion of chloroform, mercury is 2.3 kJ/mol. What is the entropy change of the system when 4 moles of mercury liquid are frozen (Le. crystallized) to the solid at -39 °C? (A) +9.8 J/K B) —39.3 J/K (c) -9.81J/K (D) +303 J/K 13. The reaction A —) B is exergonic at 25 °C and the enthalpy change is +20 kJ. What can be concluded about the entropy change for this reaction? m‘ (B) AS > +800 J/K (C) AS < -67 J/K (I ‘o conc usion can be made about AS 14. For the endergonic reaction C ——) D, AS: +20 J/K. For this reaction, (A) AG<0 & AH<0 (B) AG>O & AH<0 (o) AG<O & AH>0 D) AG>0 & AH o 15. The Enthalpy of Vaporization of methanol is 35.3 kJ/mol. The Entropy of Vaporization of methanol is 105 J/mol-K. What is the Gibbs Energy change for the condensation of one mole of methanol gas at 30 °C? (A) +3.5 kJ/mol (B) OkJ/mol (D) -32.2 kJ/mol 16. A hypothetical polypeptide, PP, has two structuraifonns, PP(0L) and PP(B). For the transition PP(a) —+ PP(B), the entropy change is +120 J/mol-K and the enthalpy change is +42 kJ/mol. Over what temperature range is this transition spontaneous? (A) Below 77 °C B) Above 77 ° (C) Below 350 °C (D) Above 350 °C 17. As discussed in class, hydrophobic (non-polar) amino acid sidechains tend to reside in the interior of proteins' tertiary structure. The reason they do _I_'I_O_t reside on the exterior of the protein is that they would rrounding water molecules (C) raise the enthalpy of the surrounding water molecu es (D) hydrogen bond with the surrounding water molecules 18. Mookie McKat (MM) recently developed a new, high efficiency, cycle for the metabolism of glucose. In the MM cycle, the metabolism of one mole of glucose to C02 and H20 converts 25 moles of ADP to ATP. lf AG° = 30 kJ for the conversion of one mole of ADP to ATP, and the MM cycle has an efficiency of 70%, then AG° for the metabolism of one mole of glucose is (B) -525 kJ (C) +525 kJ (D) -2880 kJ 19. The melting point of benzene is 6 °C, the Enthalpy of Fusion is 9.9 kJ/mol, and the constant pressure molar heat capacity of liquid benzene is 136 J/mol-K. When two (2) moles of liquid benzene at 75 °C is cooled at constant pressure to 6 °C, and then frozen to the solid, the enthalpy change is approximately <A)-18.8 m (B) +1.0 kJ (o) 49.3 kJ B C For #20 - #23 consider the I phase diagram to the right P A T—> 20. The slope of curve A-B is negative because (A) Sm(|iQ)>Sm sol) (B) Sm(|iQ)<Sm(80|) <D)vm<uq)>vm(sol) 21. The slope of curve A—D is steeper than the slope of curve A-C because <8) maps > A...s (C) AsubV > AvapV (D) AsubV < Avapv 22. If the pressure on this substance is increased from 1 bar to 500 bar, the melting point will and the boiling point will A decrease, increas- (B) increase, increase (C) increase, decrease (D) increase/decrease depends on relative solid and liquid entropies, increase 23. At temperatures above the triple point temperature, this substance can exist as: (A) vapor onl (B) solid or vapor only ( C) liqid or vapor only (D) solid or liquid or vapor PART II. PROBLEMS (Show work for partial credit) (10) 1. From the following enthalpies of reaction, j) 4 0(3) + 2 H2(g) —> 2 CzH2(g) AH = +453.6 kJ 13 002(9) —> 0(8) + 02(9) AH = +3935 kJ .32 H2(Q)+(1/2)02(9) —+ H200) AH=-285-8 '0 Calculate AH for the reaction, CzH2(g) + (5/2) 02(9) —) 2 C02(g) + H20(l) (12) 2. The constant pressure molar heat capacity of water vapor is 33.6 J/mol-K. The ' molar enthalpy of vaporization of water is 40.7 kJ/mol at 100 °C. Calculate the «if: ii? a, "3%? (entropy and enthalpy changes, AS and AH, when one mole of water vapor is cooled m?“ “ “ ” flaiéat constant pressure from 200 °C to 100 °C and then condensed to the liquid; i.e. for flthe process H20(gas,200 °C) —> H20(liq,100 °C). .fiLif/i/ V73/(5' fio/jjg73/D Q§ A’fli/ééfj 273,k) A’ f f X f m ‘ fl AS; ? y? Ck?” ,&»« E31}: / (;3,{)IZ{:::) 2: “£5 V ’\ (9) 3. The_ riormal boiling point of liquid pyridine is 116 °C, and the vapor pressure of liquid pyridine is 4.3 kPa at 40 °C. Calculate the Enthalpy of Vaporization of pyridine. 67/ém 1/W/{ij 7;: ///E,¢“>>3: 3?”? K ...
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