CH 101 notes 10-17

CH 101 notes 10-17 - Bond Energies Components of a chemical...

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Reactants ! Products Components of a chemical reaction: Break Bonds Between Atoms ! Make New Bonds Between Different Atoms requires energy endothermic Hº>0 gives off energy exothermic Hº<0 Section 9.4 H rxn ~ Σ # (broken bond) xD (broken bond) Σ # (formed bond) xD (formed bond) Table 5 Common bond energies (kJ/mol) From online CAMS, D. Wertz C-H 413 N-H 391 O-H 463 H-H 436 C-F 485 N-F 272 O-F 190 H-F 565 F-F 159 C-Cl 328 N-Cl 200 O-Cl 203 H-Cl 431 Cl-Cl 243 C-Br 276 N-Br 243 O-Br 235 H-Br 366 Br-Br 193 C-I 234 O-I 234 H-I 299 I-I 151 C-C 347 N-N 163 C-N 293 C-O 358 O-O 146 C=C 612 N=N 418 C=N 615 C=O 799 O=O 495 C C 820 N N 941 C N 891 C O 1072 H C CCCH H H H H H C CCCH H H H H HH + HH Estimate H for the following rxn reactants product Section 9.4 Circle what doesn’t change and ignore it H rxn ~ Σ # (broken bond) xD (broken bond) Σ # (formed bond) xD (formed bond) H rxn ~ +(C C) + (H-H) - (C=C) - 2(C-H) H rxn ~ + (820) + (436) - (612) - 2(413) ~ -182 kJ H C CCCH H H H H H C CCCH H H H H HH + HH Estimate H for the following rxn Section 9.4 Or, if it bothers you to spot changes, just break every reactant bond and make every product bond H rxn ~ Σ # (broken bond) xD (broken bond) Σ # (formed bond) xD (formed bond) H rxn ~ 6(C-H) + 2(C-C) + (C C) + (H-H) - 8(C-H) – 2(C-C) - (C=C) 2 H rxn ~ +(C C) + (H-H) - (C=C) - 2(C-H) H ~+(N N) + 3(H-H) -6(N-H) Estimate H for the following rxn H ~ + (941) + 3(436) -6(391) ~ -97 kJ Section 9.4 products reactants N N H H H H H H N H H H N H H H Lewis Structure Needed! N 2 (g) + 3H 2 (g) 2NH 3 (g) Estimate H for the following rxn H = -97 kJ per 2 mol NH 3 (g) produced Section 9.4 N 2 (g) + 3H 2 (g) 2NH 3 (g) H = -97 kJ per 3 mol H 2 (g) consumed H = -97 kJ per 1 mol N 2 (g) consumed What is H if 6 mol of NH 3 (g) is produced? How much heat is produced if 0.33 mol of N
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CH 101 notes 10-17 - Bond Energies Components of a chemical...

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