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Environmental Chemistry

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ENV440 - Examination 3 (100 points)

Chemistry 440--Environmental Chemistry

Examination 3, 100 points Name_________________________

April 29, 2002

 

1. (10 points) Write the correct definition, as it applies to environmental chemistry, for each of the following terms:

a. Troposphere

 

b. Mesosphere

 

c. Aerosol

 

d. Visibility (as an air quality parameter)

 

e. Non-methane hydrocarbons

 

 

2. (15 points) Dry air, at one atmosphere and 25 ° C, contains 2.46 X 1019 molecules per cubic centimeter. Calculate the number of molecules in one cubic centimeter of dry air at an altitude of 40 km, where the temperature would be -23° C. Assume ideal gas behavior (PV = nRT) and that the pressure at 45 km can be calculated from the relationship:

The average molar mass of air is 28.97 g/mol and Avagadro’s number is 6.02 X 1023.

 

 

 

 

3. (15 points). Calculate the settling velocity of a particle having a density of 0.90 g/cm3 in air at 1.00 atm pressure and 0 °C temperature, and a Stokes diameter of 0.08 microns. The viscosity of air at 0 °C is 170.8 micropoise. The density of air under these conditions is 1.29 g/L.

 

 

 

 

 

 

4. (12 points) Particulate matter in the atmosphere interacts with light in several different ways. Use diagrams and words to describe the physical processes involved in each of the following terms, as they relate to atmospheric visibility.

 a. Forward Scattering

 b. Backward Scattering

 c. Rayleigh Scattering

 d. Absorption

 

 

5. (6 points) Describe a situation, using a diagram if necessary, where a vewier would perceive atmospheric haze to appear "white."

 

 

 

 

 

6. (12 points) Listed below are a series of common air pollutants. For each air pollutant shown, state (1) whether is it expected to have a direct effect or a secondary effect on air quality, and (2) draw the structure of the first product formed from the reaction of this substance with the hydroxyl radical (HO•).

 

 

 

 

 

7.  (9 points) List the three equations, known as the Chapman Cycle, that are responsible for a steady-state concentration of ozone in the stratosphere.

 

 

 

 

 

 

 

8. (9 points) List the two equations that show how chlorine atoms (or nitrogen oxide or chlorine oxide) react with ozone to form diatomic oxygen. Give the net, overall, reaction for this process.

 

 

 

 

10. (12 points) Figure 13.4, from pg. 390 in Manahan, is shown below. Use equations from the generalized reaction mechanism for photochemical smog formation to answer the following questions.

a. Why does the atmospheric concentration of non-methane hydrocarbons peak at 8:00 a.m., and then decrease throughout the day?

 

 

 

 

b. Why does the atmospheric concentration of aldehydes peak at 1:00 p.m., and then decrease throughout the afternoon?

 

 

c. Why does the atmospheric concentration of oxidants (PAN) peak at 3:00 p.m.?

 

 

 

Useful Equations, CHM 440

pE = -log(ae-) pH = -log(aH+) Ka1, H2CO3 = 4.45 x 10-7 Ka2, H2CO3 = 4.7 x 10-11

Ksp, CaCO3 = 4.8 x 10-9 Ka, NH4+ = 5.7 x 10-10

 

a H2CO3 = a HCO3- =

 

a CO3-2 =

1/2 NO3- + H+(w) + e- ® 1/2 NO2- + 1/2 H2O pE° = +14.15

1/8 NO3- + 5/4 H+(w) + e- à 1/8 NH4+ + 3/8 H2O pE° = +14.90

1/6 NO2- + 4/3 H+(w) + e- à 1/6 NH4+ + 1/3 H2O pE° = +15.14

[X(aq)] = K Px Ph = Poe-Mgh/RT

 

Physical constants: g = 981 cm/s2 R = 0.0821 L-atm/mol-deg; R = 8.314 x 107 erg/mol-deg

R = 8.314 J/mol-deg; R = 1.98 cal/mol-deg; h = 6.63 x 10-34 J-s

blueback.gif (1060 bytes) ENV 440 Exams

 

Environmental Chemistry -- ENV 440
Last Updated:  04/22/2004