Answer Key for SAMPLE EXAMINATION #3 Dr. Slaughter, Instructor NOTE: This Sample Exam is from a previous General Chemistry for Engineers class taught by Dr. Slaughter at a different institution. Some topics on this Exam may not be covered in 1410, and those that are covered were taught in a different order. This Sample Exam is intended to give you a general idea of the type and difficulty of questions I tend to use for different chemistry topics. It is NOT intended to be a study guide or a substitute for studying the lecture notes or problem sets. Correct answers shown in bold italics. (Questions X-1 to X-4): Consider the reaction 2N2O5(g)  4NO2(g) + O2(g) Given the following thermodynamic data: N2O5 NO2 O2 X-1. 355.3 J/K·mol 239.9 J/K·mol 204.8 J/K·mol 115.20 kJ −155.20 kJ 110.02 kJ 21.86 kJ −21.86 kJ −115.6 J/K −249.2 J/K 249 J/K 89.5 J/K 453.8 J/K Calculate ΔG° for the reaction at 25 °C. A) B) C) D) E) X-4. 11.29 kJ/mol 33.15 kJ/mol 0 Calculate ΔS° for the reaction. A) B) C) D) E) X-3. S° Calculate ΔH° for the reaction. A) B) C) D) E) X-2. ΔH°f −135 kJ −11.2 kJ 98.7 kJ −25.2 kJ 245 kJ Under what conditions is the above reaction spontaneous? A) B) C) D) E) Spontaneous at all temperatures Spontaneous at low temperatures only Spontaneous at high temperatures only Spontaneous only at T=242 K. Not spontaneous at any temperature. 1 X-5. Given the following data:  NH3(g) 1/2N2(g) + 3/2H2(g) 2H2(g) + O2(g) ΔG° = +17.0 kJ  2H2O(g) ΔG° = −458 kJ Calculate ΔG°rxn for the following reaction: 2N2(g) + 6H2O(g) A) B) C) D) E) X-6.  3O2(g) + 4NH3(g) 1.31 x 103 kJ 1.42 x 103 kJ 2.68 x 103 kJ 2.82 x 103 kJ −2.68 x 103 kJ Which statement about the above reaction is true? A) It is spontaneous at 25 ºC. B) It is not spontaneous at 25 ºC. C) There is not enough information to determine whether it is spontaneous at 25 ºC. X-7. Predict the sign of ΔS for the following reaction: CH4(g) + 2H2O(g) A) B) C) D) X-8.  CO2(g) + 4H2(g) Negative Positive Neither negative nor positive (ΔS°=0) Not enough information to determine whether positive or negative. Predict the sign of ΔS for the following reaction: TiO2(s) + 2C(s) + 2H2O(g) A) B) C) D) X-9.  TiCl4(g) + 2CO(g) Negative Positive Neither negative nor positive (ΔS°=0) Not enough information to determine whether positive or negative. Which of the following is true regarding production of H2(g) fuel by electrolysis of water: 2H2O(g) A) B) C) D) E)  O2(g) + 2H2(g) It is an endothermic reaction It has an unfavorable entropy change It is currently more economical than producing H2(g) from methane It happens spontaneously when sunlight shines on seawater It is impossible to make hydrogen this way 2 X-10. An organic compound having the formula C6H12 could be which of the following: A) B) C) D) E) A “straight-chain” alkane An alkene An alkyne An alcohol A fatty acid X-11. What is the correct systematic name of the organic compound shown below? H3C A) B) C) D) E) C C CH3 2-butylane 2-butyne 2-butene 2-butone methylpropylene X-12. What is the correct systematic name of the organic compound shown below? A) B) C) D) E) 2-butylhexane trimethylheptene 1,4,7-trimethylheptane 5-propylhexane 5-methylnonane X-13. What is the correct systematic name of the organic compound shown below? A) B) C) D) E) butanoic acid 4-butyric acid pentanoic acid 1-keto-1-pentanol linoleic acid 3 X-14. Which of the following polymers is synthesized by an addition polymerization reaction? A) B) C) D) E) Polyethylene Nylon-6,6 Kevlar Adipic acid None of these X-15. What is the name of the polymer shown below? CH2 CH CH3 A) B) C) D) E) CH2 CH CH3 CH2 CH CH3 n Polyethylene Nylon-6,6 Polystyrene Polymethylhexane Polypropylene X-16. Natural rubber (latex) is crosslinked to make tire rubber by reaction with: A) B) C) D) E) styrene adipoyl chloride carbon sulfur ethylene X-17. Hydrogen for fuel cell cars is stored as H2 (ℓ). What intermolecular forces hold the molecules together in this liquid? A) B) C) D) E) London dispersion forces Hydrogen bonding Dipole-dipole forces Electrostatic attraction Covalent bonding 4 X-18. Consider the following data: Compound H2O H2S H2Se H2Te Boiling Point 100 ºC -61 ºC -42 ºC -2 ºC The reason for the higher boiling point of H2O is: A) B) C) D) E) Stronger London dispersion forces Fewer valence electrons Hydrogen bonding Higher reactivity of oxygen Lower molecular weight X-19. Which is an example of a molecular solid? A) B) C) D) E) NaBr Ice Diamond Gold Ca(NO3)2 X-20. Metallic Al has a closest packed structure with layers alternating in an ABCABC pattern (i.e., every fourth layer is the same as the first). What type of unit cell does a crystal of Al have? A) B) C) D) E) Simple cubic Body-centered cubic Face-centered cubic Rhombic prism Hexagonal 5 HELP SHEET Periodic Table of the Elements 1 18 1 2 H 1.008 2 13 14 15 16 17 He 4.003 3 4 5 6 7 8 9 10 Li Be B C N O F Ne 6.941 9.012 11 10.81 12.01 14.01 16.00 19.00 20.18 12 Na Mg 22.99 24.31 3 4 5 6 7 8 9 10 11 12 25 13 14 15 16 17 18 Al Si P S Cl Ar 26.98 28.09 30.97 32.07 35.45 39.95 19 20 21 22 23 24 26 27 28 29 30 31 32 33 34 35 36 K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr 39.10 40.08 44.96 47.88 50.94 52.00 54.94 55.85 58.93 58.69 63.55 65.38 69.72 72.59 74.92 78.96 79.90 83.80 37 38 39 40 41 Rb Sr Y Zr Nb Mo Tc 42 43 45 46 47 48 49 50 51 52 53 54 Ru Rh 44 Pd Ag Cd In Sn Sb Te I Xe 85.47 87.62 88.91 91.22 92.91 95.94 (98) 101.1 102.9 106.4 107.9 112.4 114.8 118.7 121.8 127.6 126.9 131.3 55 56 57 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn 132.9 137.3 138.9 178.5 108.9 183.9 186.2 190.2 192.2 195.1 197.0 200.6 204.4 207.2 209.0 (209) (210) (222) 87 88 89 Fr Ra Ac (223) (226) (227) Electronegativities of the Elements (For Compounds, In Pauling Units) 1 H 2.1 2 Li Be B C N O F 1.0 1.5 2.0 2.5 3.0 3.5 4.0 13 Na Mg 0.9 1.2 3 K Ca Sc 0.8 1.0 1.3 4 14 15 16 17 18 He -Ne -- Al Si P S Cl 9 10 11 12 1.5 1.8 2.1 2.5 3.0 Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br 1.6 1.9 1.9 1.9 1.6 1.6 1.8 2.0 2.4 2.8 Kr -- 5 6 Ti V 1.5 1.6 7 1.5 8 1.8 Ar -- Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe 0.8 1.0 1.2 1.4 1.6 1.8 1.9 2.2 2.2 1.9 1.7 1.8 1.9 2.1 2.5 -- Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At 0.7 0.9 1.1 1.3 1.5 1.7 1.9 2.2 2.2 2.2 2.4 1.8 1.9 1.9 2.0 2.2 Rn -- Fr Ra Ac 0.7 0.9 1.1 2.2 6 1.7 1.9 Electron Pair Geometries # e- Pairs* e- Pair Geometry Ideal Angle Between e- Pairs Hybridization 2 Linear 180° sp 3 Trigonal planar 120° sp2 4 Tetrahedral 109.5° sp3 5 Trigonal bipyramidal axial-equatorial: 90° sp3d equatorialequatorial: 120° 6 Octahedral sp3d2 90° 7 Prefixes for Compound Names (Inorganic Compounds) Prefix # of Atoms mono1 di2 tri3 tetra4 penta5 hexa6 hepta7 octa8 nona9 deca10 Conversion Factors 1 atm = 760 Torr 1 J = 1 kg·m2/s2 1 cm = 10-2 m 1 nm = 10-9 m 1 kJ = 1000 J 1 Hz = 1 s-1 T(K) = T(°C) + 273.15 Constants R = 0.08206 L·atm/mol·K (pressure units) = 8.31451 J/mol·K (energy units) Prefixes for Organic Compound Names Prefix # of Carbons meth1 eth2 prop3 but4 pent5 hex6 hept7 oct8 non9 dec10 Avogadro’s Number 6.022 x 1023 mol-1 Molar gas volume 22.4 L Gas Laws Boyle’s Law P1V1 = P2V2 Charles’s Law V1 V2  T1 T2 Ideal Gas Law PV = nRT Graham’s Law of Effusion r1 M2  r2 M1 8