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8 Chemical Bonding Solutions to Exercises 8.97 (a) AH = 5D(C-H) + D(C-C) + D(C-O) + D(O-H) - 6D(C-H) - 2D(C-O) = D(C-C) + D(O-H) - D(C-H) - D(C-O) If 348 kJ + 463 kJ - 413 kJ 358 kJ AH = +40 kJ; ethanol has the lower enthalpy (b) AH = 4D(C-H) + D(C-C) + 2D(C-O) - 4D(C-H) - D(C-C) - D(C=O) = 2D(C-O) - D(C=O) = 2(358 kJ) - 799 kJ = acetaldehyde has the lower enthalpy (c) = 8D(C-H) + 4D(C-C) + D(C=C) - 8D(C-H) - 2D(C-C) - 2D(C=C) = 2D(C-C) - D(C=C) = 2(348 kJ) - 614 kJ = +82 kJ; cyclopentene has the lower enthalpy (d) AH = 3D(C-H) + D(C-N) + D(C ≡ N) - 3D(C-H) - D(C-C) - D(C N) = D(C-N) - D(C-C) = 293 kJ - 348 kJ AH = -55 kJ; acetonitrile has the lower enthalpy H H H 8.98 (a) 4 H C 6 + 12 0=C=0 + 10 + N N N nitroglycerine = 20D(C-H) + 8D(C-C) + 12D(C-O) + 24D(O-N) + 12D(N=O) - [6D(N N) + 24D(C=O) + 20D(H-O) + D(O=O)] = 20(413) + 8(348) + 12(358) + 24(201) + 12(607) - [6(941) + 24(799) + 20(463) + 495] = kJ 1.00 g C₃H₅N₃O₉ 227.1 1 mol g C₃H₅N₃O₉ C₃H₅N₃O₉ 4 mol -7129 C₃H₅N₃O₉ kJ = 7.85 kJ/g C₃H₅N₃O₉ (b) 4C₇H₅N₃O₆(s) + + 10H₂O(g) + 21C(s) 221