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Chapter 8 Chemical Bonding

Values q this is only an approximate hrxn this 5

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Unformatted text preview: q Use bond energies to calculate the enthalpy Use change for the following reaction: change N2(g) + 3H2(g) → 2NH3(g) (g) q ∆ Hrxn = DN ≡ N + 3DH-H - 6DN-H rxn ∆ Hrxn = 942 + 3(432) - 6(386) = -78 kJ measured value = -92.2 kJ q Why are the values different? 5 Sample Problem q Use bond energies to calculate the Use enthalpy change for the following reaction: reaction: 2CO(g) + O2(g) → 2CO2(g) (g) DC ≡ O = 1072 kJ DO = O = 492 kJ DC = O = 799 kJ q ∆ Hrxn = 2DC ≡ O + DO = O - 4DC = O 2D rxn ∆ Hrxn = 2(1072) + 492 - 4(799) = -560 kJ 5 Bond Energy and Bond Length q The distance between the nuclei of the atoms The involved in a bond is called the bond length. involved q Multiple bonds are shorter than single Multiple bonds. bonds. q Multiple bonds are also stronger than single Multiple bonds. bonds. q As the number of bonds between two atoms As increases, the atoms are held closer and more tightly together. more 6 Bond Lengths 6...
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