Chapter 9.10 as handout

Chapter 9.10 as handout - change for: H 2 ( g ) + F 2 ( g )...

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1 The bond energy is the enthalpy change required to break a particular bond in one mole of gaseous molecules. H 2 ( g ) H ( g ) + H ( g ) Δ H 0 = 436.4 kJ Cl 2 ( g ) Cl ( g ) + Cl ( g ) Δ H 0 = 242.7 kJ HCl ( g ) H ( g ) + Cl ( g ) Δ H 0 = 431.9 kJ O 2 ( g ) O ( g ) + O ( g ) Δ H 0 = 498.7 kJ O O N 2 ( g ) N ( g ) + N ( g ) Δ H 0 = 941.4 kJ N N Bond Energy Bond Energies Single bond < Double bond < Triple bond 9.10 The strength of a bond depends on its environment , however. For example, the bond enthalpy of O-H depends on the molecule the bond is found in. The bond energy can be averaged for many different molecules (environments), however. H 2 O ( g ) H ( g ) + OH ( g ) Δ H 0 = 502 kJ OH ( g ) H ( g ) + O ( g ) Δ H 0 = 427 kJ Average OH bond = energy 502 kJ + 427 kJ 2 = 464 kJ 9.10 Bond Energies (BE) and Enthalpy changes in reactions Δ H 0 = total energy input – total energy released = Σ BE(reactants) – Σ BE(products) Imagine reaction proceeding by breaking all bonds in the reactants and then using the gaseous atoms to form all the bonds in the products. 9.10
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2 Example : Use bond energies to calculate the enthalpy
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Unformatted text preview: change for: H 2 ( g ) + F 2 ( g ) 2HF ( g ) H = BE(reactants) BE(products) Type of bonds broken Number of bonds broken Bond energy (kJ/mol) Energy change (kJ) H H 1 436.4 436.4 F F 1 156.9 156.9 Type of bonds formed Number of bonds formed Bond energy (kJ/mol) Energy change (kJ) H F 2 568.2 1136.4 H = 436.4 kJ + 156.9 kJ 2 x 568.2 kJ = -543.1 kJ 9.10 Example : Use bond energies to calculate the enthalpy change for: 2H 2 ( g ) + O 2 ( g ) 2H 2 O ( g ) H = BE(reactants) BE(products) Type of bonds broken Number of bonds broken Bond energy (kJ/mol) Energy change (kJ) H H 2 436.4 872.8 O O 1 498.7 498.7 Type of bonds formed Number of bonds formed Bond energy (kJ/mol) Energy change (kJ) H O 4 460 1840 H = 872.8 kJ + 498.7 kJ 1840 kJ = -469 kJ 9.10...
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Chapter 9.10 as handout - change for: H 2 ( g ) + F 2 ( g )...

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