1. (20 total) In Earth’s atmosphere, the mixing ratio of hydrogen sulfide (H2S,
ID: 899751 • Letter: 1
Question
1. (20 total) In Earth’s atmosphere, the mixing ratio of hydrogen sulfide (H2S, MW=34.09g/mol) is 100 pptv.
a) If you were to randomly select one hundred billion (1011) particles from the troposphere how many of these particles would be H2S molecules?
b) Express the tropospheric concentration of H2S in moles /m3. Assume standard temperature and pressure.
2. (20 total) If the mixing ratio of O3 is 50 ppbv, what is its concentration:
a) in mg/cm3?
b)in molecules/cm3
3. a) (20 total) Briefly describe (compare and contrast..) photolysis and photo-ionization processes. Use a few words and an equations (general or specific) to illustrate each type of process.
b) Calculate the longest wavelength (in nm) of a photon that is capable of photolyzing the carbon-carbon bond in a benzene ring. Do you predict that the photolysis of compounds with benzene rings represents a significant sink of them in the troposphere? Justify your answer.
C-C (aromatic) + photon -> fragments BDE = 518 kJ/mol
4. (20) A measurement made at ground level in Statesboro, GA indicated on a high UV Index day that there were 280 DU of ozone overhead. How many O3 molecules correspond to 280 DU assuming a column area of 1m2?
5. (20) Draw the structures of CFC-114b, CFC-115, and HCFC-22. Predict how these three compounds are expected to rank in terms of their tropospheric lifetimes. Explain your predictions.
Each of these are greenhouse gases. Can you predict how these compounds qualitatively rank in terms of their global warming potentials?
Explanation / Answer
In Earth’s atmosphere, the mixing ratio of hydrogen sulfide (H2S, MW=34.09g/mol) is 100 pptv.
a) If you were to randomly select one hundred billion (1011) particles from the troposphere how many of these particles would be H2S molecules?
pptv= parts per trillion volume
1 pptv = 1x10-12 mol/mol
given that; hydrogen sulfide (H2S, MW=34.09g/mol) is 100 pptv means 100 H2S present in per trillion volume.
one thousand billion = one trillion
one hundred billion = 0.1 trillion
one trillion volume contains = 100 particles H2S
0.1 trillion will contain = 100 particles H2S / one trillion * 0.1trillion = 10 particels.
b) Express the tropospheric concentration of H2S in moles /m3. Assume standard temperature and pressure.
1 pptv= 1 part per trillion or 1 g chemical per trillion (1012) volume.
calculate the number of moles of H2S = 100 g / 34.09g/mol = 2.93 mol
trillion (m^3) = 1 000 000 000 000 m^3
The concentration of H2S in moles /m3 = 2.93 mol / 1 000 000 000 000 m^3
= 2.93*10^-12 moles /m3
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