Nitrogen Exercises

Some of these questions make reference to the assigned papers for today, so please make sure to read them before attempting to answer the questions below. In addition, there are very nice tutorials on photoelectron spectroscopy available from the Center for Gas-Phase Electron Spectroscopy. Lectures 2 and 3 available there in PowerPoint format contain much helpful information about N2 photoelectron spectra.
  1. The bond dissociation energy for N2 is ca. 946 kJ/mol, making for one of the strongest bonds known in all of chemistry. Given bond energies of 436, 391, and 159 kJ/mol, respectively, for H-H, N-H, and N-N single bonds, calculate the enthalpy of reaction for the dissociation of hydrazine (N2H4) into N2 + 2 H2.
  2. Look up the heat of formation of hydrazine in the NIST chemistry webbook. How does the number you find there compare to the number you calculated in the previous question?
  3. What does the value of the hydrazine heat of formation mean with respect to the stability of hydrazine?
  4. Look up the heat of formation of CO2 in the NIST chemistry webbook. Compare the sign and the magnitude of the CO2 heat of formation with that of hydrazine, and put into context what you know about the chemical stability of these two molecules.
  5. With reference to the paper on the photoelectron spectrum of N2, make a sketch of the spectrum in the 15-20 eV energy range.
  6. On your sketch from the preceding problem, near each manifold of peaks, draw a sketch of the nitrogen molecular orbital that has been ionized to give rise to that peak manifold.
  7. How many of the N2 MOs give rise to peaks in this 15-20 eV range?
  8. Ionization of which N2 molecular orbital gives rise to a peak manifold manifesting the greatest amount of vibrational fine structure? Draw this molecular orbital give a brief interpretation of the fine structure.
  9. Explain why it is that the HOMO of N2 does not correspond to the molecule's pi bonds.
  10. With reference to the paper on the photoelectron spectrum of N2, write down the term symbol corresponding to each of the following configurations: (1σg)2(1σu)2(1πu)4(2σg)1, (1σg)2(1σu)2(1πu)3(2σg)2, (1σg)2(1σu)1(1πu)4(2σg)2, (1σg)1(1σu)2(1πu)4(2σg)2.