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Unformatted text preview: q Use bond energies to calculate the enthalpy
change for the following reaction:
N2(g) + 3H2(g) → 2NH3(g)
q ∆ Hrxn = DN ≡ N + 3DH-H - 6DN-H
∆ 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
enthalpy change for the following
2CO(g) + O2(g) → 2CO2(g)
DC ≡ O = 1072 kJ
DO = O = 492 kJ
DC = O = 799 kJ q ∆ Hrxn = 2DC ≡ O + DO = O - 4DC = O
∆ Hrxn = 2(1072) + 492 - 4(799)
= -560 kJ 5 Bond Energy and Bond
q The distance between the nuclei of the atoms
involved in a bond is called the bond length.
q Multiple bonds are shorter than single
q Multiple bonds are also stronger than single
q As the number of bonds between two atoms
increases, the atoms are held closer and
more tightly together.
more 6 Bond Lengths 6...
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This note was uploaded on 09/24/2012 for the course CHM 113 taught by Professor Anbar during the Spring '06 term at ASU.
- Spring '06