Chemical Kinetics and Dynamics: Ozone Formation and Chlorofluorocarbons - Prof. Philip R. , Study notes of Chemistry

Download Chemical Kinetics and Dynamics: Ozone Formation and Chlorofluorocarbons - Prof. Philip R. and more Study notes Chemistry in PDF only on Docsity! Chemical Kinetics & Dynamics Chem 415/515 Fall 2008 http://python.rice.edu/~brooks/Chem515/home.html November 18 2008 Ozone Formation in atmosphere 1 O 2 + h! "O +O * Chapman 1930 (! < 200nm) ! 1 = 2.5x10 "12 s "1 midday @ 30km 2 O + O2 + M → O3 + M k2=7.2x10-8 M-2s-1 3 O 3 + h! " O 2 +O (210 < ! < 290nm) ! 3 = 3.2x10 "4 s "1 4 O + O3 → 2O2 k4=3.8x105 M-2s-1 d[O] dt = 2R 1 ! R 2 + R 3 ! R 4 = 0 d[O 3 ] dt = R 2 ! R 3 ! R 4 = 0 R 1 = R 4 R 2 = R 3 + R 4 ! R 3 ! 1 [O 2 ] = k 4 [O][O 3 ] k 2 [O][O 2 ][M ] = ! 3 [O 3 ] [O 3 ] [O] = k 2 [O 2 ][M ] ! 3 ! 10 4 "10 6 1994--Montreal Protocol bans CFCl’s O3 levels have stopped decreasing and starting to Go up. use CHF2Cl--more reactive in troposphere: Reacts before getting to stratosphere CHF2Cl + OH → CF2Cl + H2O But: Antarctic ozone hole Daily Average 20 km O, Density Events Inside of Polar Vortex T T T T T 5 2 & > 3 a é THETTP TTT TT sesietibisparireiterririeriterrrisiitieriseiis Polar Stratospheric Clouds a eters Nitric acid trihydrate (HNO -3*H20) Ternary solution (H20, H,SO,4, HNO3) Formation Temp: SEE a 4 atm Cs 1pm Altitudes: eer at Toate ee SRR EWE Bey eons Water Ice eC UC 188K Particle diameter: Pee) Altitudes: ae a) Settling rates: Pa Cree ha Type II PSC cloud Heterogeneous reactions take place on PSCs, releasing chlorine from HCI and CIONO, into icra lee cen OR Rat Ome rit t tick Cree CeO OO eee) Q • T [ ]high [ ]low Tsteady Tignition Explosions H2 & O2 2:1 T ! 600 T ! 460 460 ! T ! 600 Explodes at any P No explosion Depends on P T P 1 10 100 1000 Steady reaction Explosion P (torr) 500K Steady reaction Steady reaction Explosion Explosion ≈2 ≈100 ≈260 2H2 + O2 --> 2H2O ∆H=-241.8kJ/mole 1st Limit sensitive to surface type and amount 2nd limit not sensitive to surfaces Rate decreases H2-->2H ∆E=4.5 eV O2-->2O ∆E=5.1 eV initiation r0 H+O2 --->OH + O O + H2--->OH + H ∆H=+0.7 eV ∆H=+0.1 eV Few kT Endo Branching k2 k3 H + wall--->1/2 H2 H + O2+ + M -->HO2 + M termination k5 k6 Reaction Mechanism OH + H2--->HOH + HO, OHconsumed k4 ∆H=-0.7 exo Note: in the overall reaction 3 bonds are broken but 4 are made