What’s coming up???

1. What’s coming up??? • Oct 25 The atmosphere, part 1 Ch. 8 • Oct 27 Midterm … No lecture • Oct 29 The atmosphere, part 2 Ch. 8 • Nov 1 Light, blackbodies, Bohr Ch. 9 • Nov 3 Postulates of QM, p-in-a-box Ch. 9 • Nov 5,8 Hydrogen atom Ch. 9 • Nov 10,12 Multi-electron atoms Ch.10 • Nov 15 Periodic properties Ch. 10 • Nov 17 Periodic properties Ch. 10 • Nov 19 Valence-bond; Lewis structures Ch. 11 • Nov 22 Hybrid orbitals; VSEPR Ch. 11, 12 • Nov 24 VSEPR Ch. 12 • Nov 26 MO theory Ch. 12 • Nov 29 MO theory Ch. 12 • Dec 1 Putting it all together • Dec 2 Review for exam

2. The atmosphere • Made up of a mixture of gases (mainly N2 and O2) • Mole fractions of major gases (nitrogen, oxygen, carbon dioxide, argon) are pretty constant with altitude • “interesting stuff” involves tiny amounts of trace gases – ozone, oxides of nitrogen and sulfurand some others

3. ~ 100%

5. Breathing!!!

6. Argon, Neon, Xenon … rare gases often used in “neon” lights

7. Atmospheric gases can be separated by distillation, since they have different boiling points N2 77 K O2 90 K Ar 87 K Ne 24 K CH4 111 K

9. Pressure profile of atmosphere Pressure drops almost exponentially with increasing altitude ... why?? Trop. Strat.

10. Temperature profile in the atmosphere stratosphere

11. T goes up p stays constant Therefore, density goes down • pV = nRT ideal gas law is “pretty good” (why??) • Sun warms Earth’s surface … p is constant, so (n / V) decreases … p = (n/V) RT

12. Warmer, less dense air rises and expands … • work done against the surroundings … • … internal energy is lost • …. Therefore the air parcel cools

13. Temperature profile in the atmosphere stratosphere

14. The warming that happens through the stratosphere is due to chemical reactions which release heat … exothermic • These reactions involve ozone chemistry: O2 + UV light  O + O heat released O + O2 + M  O3 + Mheat released (M is required to remove excess energy) O + O3  2 O2 heat released O3 + UV light  O2 + Oheat released

15. Outer space Heating due to Ionic reactions Cooling again

16. Aurora borealis: Northern lights are actually due to ions in the ionosphere reacting with charged particles from the solar wind

17. Equilibrium vapour pressure of water Relative humidity > 100% water condenses Relative humidity < 100% water evaporates

19. High altitude clouds (like cirrus clouds) are generally made of ice crystals Lower clouds (rain clouds!) are composed of liquid water droplets

21. Ozone in the atmosphere Most of the atmospheric ozone is in the stratosphere, in the “ozone layer”

22. Basic ozone chemistry: • O2 + UV light  O + O heat released • O + O2 + M  O3 + Mheat released • (M is required to remove excess energy) • O + O3  2 O2 heat released • O3 + UV light  O2 + Oheat released • The ozone layer exists because of a balance between formation and destruction reactions

23. DH0f (O2) = …. DH0f (O3) = 142.7 kJ/mol DH0rxn = 2DH0f (O3) -3 DH0f (O2) = -285.4 kJ/mol

24. Ozone absorbs dangerous wavelengths of solar radiation in the stratosphere (where the ozone concentration is high) before it can reach the surface of the earth O3 + UV light  O2 + O

26. These help to destroy ozone in the stratosphere Almost entirely from humans!

27. These chemical cycles are faster than the reactions which only involve oxygen species. They are most important in the Antarctic (and sometimes the Arctic) regions of the stratosphere, during the local springtime (late Sept-Nov in Antarctica)

28. Early spring Depleted ozone correlates with increased ClO

29. Ozone “hole”

31. Toronto The decrease in ozone concentration in the stratosphere has resulted in an increase of the UV light which is no longer absorbed there

32. Up-to-the-minute newsbreak! What’s up with this year’s ozone hole? Go to http://jwocky.gsfc.nasa.gov/