CHEM: Calculate the ΔH of the following reaction: N2(g) + 3H2(g) → 2NH3(g)?

Bond dissociation energy data

N–N (triple bond) = 945 kJ / mol

H–H = 436 kJ / mol

N–H = 391 kJ / mol

OPTIONS:

1538 kJ

−769 kJ

−93 kJ

113 kJ

2 Answers

  • Reactants: N triple bond N = 945

    H-H = 436 x 3 = 1308

    Total reactant bond energy = 2253 kJ

    Products: N-H = 391 x 3 = 1173 x 2 = 2346 kJ total for products

    2253 - 2346 = -93 kJ

  • Some examples of what to do:

    http://chemteam.info/Thermochem/HessLawIntro3.html

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