Ch9_BE - 1 Using Bond Energies 2 Using Bond Energies...

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Unformatted text preview: 1 Using Bond Energies 2 Using Bond Energies Estimate the energy of the reaction H—H + Cl —Cl ----> 2 H— Cl Net energy = Hrxn = Net = energy required to break bonds energy - energy evolved when bonds are made energy ----> O=O + 2 H—O—H Energy required to break bonds: Estimate the energy of the reaction 2 H—O—O—H ----> O=O + 2 H—O—H Cl—Cl = 2242kJ/mol Cl—Cl = 42 kJ/mol H—Cl = 432 kJ/mol H—Cl = 432 kJ/mol Is the reaction exo- or endothermic? Sum of H-H + Cl-Cl bond energies = 436 kJ + 242 kJ = +678 kJ Which is larger: A) Net = H = +678 kJ - 864 kJ = -186 kJ 5 Using Bond Energies 2 H—O—O—H ----> O=O + 2 H—O—H Net energy = +2144 kJ - 2350 kJ = - 206 kJ Net energy = +2144 kJ - 2350 kJ = - 206 kJ break 4 mol of O—H bonds = 4 (463 kJ) break 2 mol O—O bonds = 2 (146 kJ) The reaction is exothermic! The reaction is exothermic! TOTAL ENERGY to break bonds = 2144 kJ TOTAL ENERGY to break bonds = 2144 kJ More energy is evolved on More energy is evolved on making bonds than is making bonds than is expended in breaking expended in breaking bonds. bonds. TOTAL ENERGY evolved on making O=O TOTAL ENERGY evolved on making O=O bonds and 4 O-H bonds bonds = 2350 kJ bonds and 4 O-H bonds bonds = 2350 kJ Page 1 energy req’d to break bonds energy req’d B) 2 mol H-Cl bond energies = 864 kJ mol H-Cl bond 4 2 H—O—O—H Using Bond Energies Estimate the energy of the reaction H—H = 436 kJ/mol H—H + Cl —Cl ----> 2 H— Cl H—H = 436 kJ/mol H—H = 436 kJ/ mol H—H = 436 kJ/mol Cl— Cl = 242 kJ/mol Cl—Cl = 242 kJ/mol H—Cl = 432 kJ/mol H—Cl = 432 kJ/mol Using Bond Energies 3 or energy evolved on making bonds? ...
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This note was uploaded on 10/19/2011 for the course CHM 2210 taught by Professor Staff during the Spring '08 term at University of Central Florida.

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