CH 301 Chapter 6 notes part 3

CH 301 Chapter 6 notes part 3 - CH301 Notes Chapter 6 part...

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CH301 Notes Chapter 6 part 3 Bond Energy amount of energy required to break a bond and separate the atoms in the gas phase. Breaking bonds always requires energy ! HCl (g) Æ H (g) + Cl (g) Δ H = +432 kJ/mol ALL B.E. VALUES ARE POSTIVE!! Bigger B.E. = more stable bond = harder to break. BE can be measured directly in some cases. BE can be measured via Hess’ Law using Δ H º f (see below) BE can come from heat or light For GAS PHASE REACTIONS ONLY: Δ H o rxn = Σ BE reactants - Σ BE products If all BE’s known: can calculate Δ H o rxn If Δ H o rxn is known: can calculate BE from other BE’s, or, Δ H o f ‘s Example: Calculate the bond energy for hydrogen fluoride, HF. 2. Calculate the average N-H bond energy in ammonia, NH 3 AVERAGE Bond Energies have been measured and tabulated. . Here’s ours for HW and exams:
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Bond Energy Table Notes: See your book: pages 234, 235: Tables 6.7 and 6.8 Exact values of BE differ slightly for same bond in different compounds - can be overlooked Single bonds weaker (lower BE) than double bonds
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CH 301 Chapter 6 notes part 3 - CH301 Notes Chapter 6 part...

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