ATMOSPHERIC CHEMISTRY
AOSC/CHEM 637
Homework #2 (Thermodynamics)
Due February 25, 2010
CIRCLE YOUR ANSWERS
1. (4) The following statement appears in an article entitled Pollution and Climate Change by J.E. Lovelock (Atmos. Environ., 5, 403, 1971):
Until recently the atmosphere was looked on as if it were a leftover from primeval inorganic chemistry, a mixture of gases ejected from the Earth's interior and transformed once and for all by photochemistry in the upper air into the composition we now know, but if inorganic chemistry alone mattered, by now all the Earth's nitrogen should be in the sea as salts of nitric acid, for at the (oceanic) pH and oxygen partial pressure of the atmospheric environment molecular nitrogen spontaneously oxidizes to nitrate ion. That, even after 5x109 yr, the air still consists mainly of nitrogen acknowledges the overwhelming victory of biological processes over inorganic chemistry and equilibrium thermodynamics.
Justify this statement with a thermodynamic argument. You will have to assume that the amount of HNO3 equivalent to the total N2 in the atmosphere would not saturate the oceans with nitrate - prove it. What are the other important assumptions?
|
SUBSTANCE |
DHf o kcal mole-1 |
DGf o kcal mole-1 |
|
O2 & N2 |
0 |
0 |
|
H2O |
-57.8 |
-54.6 |
|
H2O(l) |
-68.3 |
-56.7 |
|
HNO3 (g) |
-32.1 |
-17.9 |
|
HNO3 (aq) |
-49.6 |
-26.6 |
|
NO2 |
8.1 |
12.4 |
|
NO |
21.6 |
20.7 |
|
H +(aq) |
0 |
0 |
|
OH -(aq) |
-55.0 |
-37.6 |
2. (4) Compute the N-O bond dissociation energy for nitric oxide, NO, and nitrogen dioxide, NO2, (the first bond only). Calculate the maximum wavelength of light that can photolyze NO2, in other words can initiate the following reaction:
NO2 + hn ® NO + O
For extra credit repeat for NO3, and explain what that tells us about the importance of NO3 during the daylight hours.
3. (2) Carbon monoxide, CO, ozone (O3), and reactive nitrogen compounds NO, NOx (the sum of NO and NO2) and NOy (NOx plus PAN, HNO3 and other N compounds), were measured simultaneously over the course of a summer day in a rural area in the eastern US. The day started out clear and then became stormy. Find the mean and standard deviation for each data set. Which species is most likely to have the longest lifetime? Calculate the correlation coefficient and "least squares" line parameters for each pair of variables. Plot the data in an understandable manner. Is it likely that CO and NOx have the same source? Suggest a likely chain of events leading to the observed mixing ratios.
8/14/91
All units ppb
|
EST |
[CO] |
[NOy] |
[NOx] |
[NO] |
[O3] |
|
0.5 |
186.0 |
2.677 |
0.453 |
0.122 |
8.00 |
|
1.5 |
195.7 |
3.341 |
0.743 |
0.039 |
14.00 |
|
2.5 |
202.1 |
2.894 |
0.804 |
0.119 |
6.00 |
|
3.5 |
214.6 |
2.488 |
0.577 |
0.151 |
3.00 |
|
4.5 |
201.1 |
2.931 |
0.554 |
0.079 |
9.00 |
|
5.5 |
190.5 |
3.494 |
0.605 |
0.061 |
15.00 |
|
6.5 |
209.2 |
3.603 |
0.824 |
0.097 |
8.00 |
|
7.5 |
181.20 |
4.154 |
0.719 |
0.139 |
11.00 |
|
8.5 |
189.0 |
5.003 |
0.750 |
0.136 |
21.00 |
|
9.5 |
182.3 |
5.386 |
0.790 |
0.097 |
26.00 |
|
10.5 |
174.5 |
4.721 |
0.716 |
0.080 |
27.00 |
|
11.5 |
189.6 |
4.384 |
0.592 |
0.080 |
27.00 |
|
12.5 |
183.1 |
5.023 |
0.955 |
0.161 |
25.00 |
|
13.5 |
214.6 |
6.662 |
1.307 |
0.211 |
34.00 |
|
14.5 |
186.6 |
5.173 |
0.941 |
0.091 |
34.00 |
|
15.5 |
181.3 |
3.313 |
0.970 |
0.104 |
39.00 |
|
16.5 |
168.8 |
2.588 |
0.808 |
0.041 |
40.00 |
|
17.5 |
158.7 |
2.363 |
1.262 |
0.056 |
41.00 |
|
18.5 |
170.5 |
3.446 |
1.929 |
0.067 |
37.00 |
|
19.5 |
165.7 |
4.541 |
2.547 |
0.057 |
39.00 |
|
20.5 |
163.6 |
4.698 |
2.024 |
0.041 |
33.00 |
|
21.5 |
167.40 |
3.995 |
1.519 |
0.051 |
28.00 |
|
22.5 |
174.08 |
4.209 |
1.595 |
0.063 |
22.00 |
|
23.5 |
174.56 |
5.545 |
2.331 |
0.058 |
24.00 |