CHEMISTRY CONCEPTS (LAST CLASS) CHEMICAL THERMODYNAMICS: steps don’t matter  final state – initial state CHEMICAL KINETICS: rates depend on series of elementary reactions that make up the reaction mechanism A + B  Ck 1 A + D  Bk 2

QUESTIONS 1.Which would have the larger atomic radius: C or O? 2.What is the oxidation state of the carbon in methanol? 3.For the reaction A + B ↔ C + D, what would be the equilibrium constant if [A] = 2[D] and [C]=[B]

Chapter 2. ATMOSPHERIC PRESSURE “SEA LEVEL” PRESSURE MAP

ATMOSPHERIC PRESSURE Pressure is the weight exerted by the overlying atmosphere: Average sea-level pressure (SLP): ≡ kPa ≡1 atm ≡ bar ≡ millibars (mbar, mb) or hectopascals (hPa) ≈ mm-Hg, 0 °C ≡760 torr ≈ cm–H 2 O, 4 °C ≈ psi

MEASURING ATMOSPHERIC PRESSURE Measurement of atmospheric pressure with the mercury barometer: vacuum AB h

MASS m a OF THE ATMOSPHERE Radius of Earth: 6378 km Mean pressure at Earth's surface: 984 hPa Total number of moles of air in atmosphere: Mol. wt. of air: 29 g mole -1 =.029 kg mole -1 P=F/A

PRESSURE-GRADIENT FORCE P(z) P(z+dz) Low Pressure F g = mg F p = [P(z)-P(z+dz)]A Pressure gradient force goes from high to low pressure slab of surface area A High Pressure

BAROMETRIC LAW (variation of pressure with altitude) Consider elementary slab of atmosphere: P(z) P(z+dz) hydrostatic equation Ideal gas law: Assume T = constant, integrate: Barometric law unit area M a = kg/mole

SEA-LEVEL PRESSURE CAN’T VARY OVER MORE THAN A NARROW RANGE: 1013 ± 50 hPa Consider a pressure gradient at sea level operating on an elementary air parcel dxdydz: P(x)P(x+dx) Vertical area dydz Pressure-gradient force Acceleration For  P = 10 hPa over  x = 100 km,  ~ m s -2  100 km/hr wind in 1 h! Effect of wind is to transport air to area of lower pressure  dampen  P On mountains, however, the surface pressure is lower, as the pressure-gradient force along the Earth surface is balanced by gravity: P(z) P(z+  z) P-gradient gravity  This is why weather maps show “sea level” isobars;  The fictitious “sea-level” pressure at a mountainous site assumes an isothermal air column to be present between the surface and sea level (at T of surface site)

VERTICAL PROFILES OF PRESSURE AND TEMPERATURE Mean values for 30 o N, March Tropopause Stratopause From 1000 hPa to 0.01 hPa:

REGIONS OF THE ATMOSPHERE Troposphere: generally homogeneous, characterized by strong mixing decreasing T with increasing altitude from heat-radiating surface near surface boundary layer exists (over the oceans ~1km depth), BL often cloud topped and can trap emissions Tropopause: serves as a “barrier” that causes water vapour to condense to ice “tropopause folding” where strat air intrudes into lower levels  exchange mechanism Stratosphere: increasing T with altitude due to OZONE causing heating from absorption of UV Mesosphere: absence of high levels of radiation absorbing species and thus a T decrease upper mesosphere and higher defines the exosphere from which molecules and ions can escape the atmosphere Thermosphere: rarified gases reach temperatures as high as 1200C by absorption of high energy radiation

BAROMETRIC LAW: THE SEA-BREEZE EFFECT ~1 km ~10 km

VERTICAL TRANSPORT: BUOYANCY Object (  z z+  z Fluid (  ’) Imagine object of same density as fluid: Note: Barometric law assumed a neutrally buoyant atmosphere with T = T’ P-gradient Gravity Now look at force imbalance when density of object differs from surrounding fluid: If object is lighter than fluid  accelerate upwards

EXAMPLE: VENUS VS THE EARTH Compare the atmospheres of Venus and Earth: VENUS EARTH g, m/s Planet radius(km) Surface pressure, atm 91 1 Temperature, T a.How does the mass of Venus’ atmosphere compare to the Earth’s? (is it larger/smaller and roughly by how much?) b.How does the scale height of Venus’s atmosphere compare to Earth’s (remember Venus’ atmosphere is mostly CO 2 )?