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22 Chemistry of the Nonmetals Solutions to Exercises 1944.1 -571.66 = 275,636 = 2.76 The minus sign indicates that energy is produced. 22.90 From Appendix C, we need only for F(g), so that we can estimate AH for the process: F₂(g) F(g)+F(g); = 160 kJ XeF₂(g) The average Xe-F bond enthalpy is thus 269/2 = 134 kJ. Similarly, XeF₄(g) = 218 kJ 2F₂(g) 4F(g) = 320 kJ XeF₄(g) = 538 kJ Average Xe-F bond energy = 538/4 = 134 kJ XeF₆(g) - = 298 kJ 3F₂(g) 6F(g) = 480 kJ XeF₆(g) Xe(g)+6F(g) = 778 kJ Average Xe-F bond energy = 778/6 = 130 kJ The average bond enthalpies are: 134 kJ; 134 kJ; XeF₆, 130 kJ. They are remarkably constant in the series. 22.91 (a) AH = -285.83 kJ/mol H₂ + AH = 2(-285.83) - 393.5 (-74.8) = -890.4 mol CH₄ (b) for H₂: -285.83 1 mol H₂ 1 mol H₂ H₂ = -141.79 kJ/g H₂ for CH₄: 1 -890.4 mol CH₄ mol CH₄ CH₄ = -55.50 CH₄ (c) Find the number of moles of gas that occupy 1 at STP: n = 273 K atm 100 1m 73 1L = 44.64 mol for -285.83 1 mol H₂ 44.64 1 m³ mol H₂ H₂ = -1.276 10⁴ kJ/m³ H₂ for CH₄: 1 -890.4 mol CH₄ 44.64 1 m³ mol CH₄ CH₄ = -3.975 10⁴ kJ/m³ CH₄ 686