Howard S. Kimmel and Don G. Lambeti Newark College of Engineering Newark, New Jersey 07102
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Developing a course a t Newark College of Engineering in physical chemistry applied to environmental problems presented several challenges. First, the students were Civil Engineering juniors or seniors with only a general chemistry background. Second, although the students had taken a course in mechanical engineering thermodynamics, they had no appreciation of the applications of thermodynamics to chemistry, and almost no background in chemical kinetics. Third, no textbook with quantitative applications of physical chemistry to environmental problems is availahle, although a useful supplement is now availahle (1). The approach decided upon was to assign readings and problems in an elementary physical chemistry text (2) to provide a background for the applications being considered in the lecture. Students were encouraged to participate in the discussions of applications with which they were familiar as well as to bring in material which they might have. Since the students had not dealt with chemistry for two or three years, the first week was devoted to a review of stoichiometry using combustion processes as an example. Specifically, the burning of one ton of coal containing 1%sulfur was considered, with how much SOz, SOa, and HzSOI could be produced, and how much iron could the sulfuric acid react with. These figures were then related to the reduction of SO2 in New York City air and to the more general problem of power production (3). Students later suggested that determination of oxygen and the difference in chemical oxygen demand and biochemical oxygen demand (4) could have been discussed a t this point. Treatment of gases was begun by computing amounts of each gas in unpolluted air, then giving estimates of each material being put into the environment (5). Next, some
Physical Chemistry for Environmental Engineers of the sources of pollution were discussed along with the chemistry involved (6). In particular, the ratios of SO31 SO2 in smokestacks were noted, along with possible processes for conversion of SOz to S o 3 in the atmosphere. Also, the NOz/NO ratio in smokestacks and automobile exhausts was presented and the question was raised as to whether NO, production is not simply a constant independent of the fuel used. One student hrought specifications for an experimental automobile using liquid propane fuel which had about ten times less NO then conventional cars, which lead to a discussion of the factors favoring NO production. The inherent difficulty of reducing both NO and CO in auto emissions was pointed out. During this time the problems in the text an gases were assigned and problems which gave the students difficulty were done in class. Later the students indicated that this survey of the chemistnr of air pollution was a valuable introduction to a subject with which they were not familiar. The first law of thermodynamics was approached from a practical viewpoint. A problem based o n a recent proposal to use steam at 250°C from power plants to heat houses was nresented and was criticized hv students who knew aboui the maze of underground plpea in urban areas. Xext quantitative problems dealing with space heating for houses were presented to rlnrify the conrept of a system. 'I'he basic components of power plants were discussed, and one student hrought some literature about the cooling towers for a new nuclear power plant. With this background, the first law of thermodynamics was developed and applied to the systems previously mentioned, as well as heat transfer in humans (7). the formation of clouds on mountains (ti), and a quantitative derivation of the adiabatic lapse rate (9) which the students had seen mentioned in a previous course in environmental engineering.
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The second law was introduced by asking what is the theoretical efficiency of a power plant, which led immediately to the Carnot cycle. The implications of the second law to thermal pollution was emphasized by showing actual efficiencies of power plants and engines. Efficiency of utilization of sunlight by organisms (10) was related to the question of whether we should eat algae or steak (11). This led to a discussion of the thermodynamics of utilization of food (12) and the efficiency of various organisms in food utilization (13). Some of the important cycles, such as that involvine nitrogen (14) were used to illustrate the application of thermod;na&ci in understanding these cycles. Next the entropy was develo~edfrom the statistical point of view and--qualitative &dictions of entropy changes in phase changes and chemical reactions were confirmed by citing numbers. The concept of the free energy was then developed and applied particularly to the combustion of carbon, nitrogen, and sulfur. It was shown that the SO2 and SOs formation reactions are spontaneous, while the formation of NO is non-spontaneous. After a review of solutions, the thermodynamics of some water treatment processes for removing calcium ion were discussed, and the reverse osmosis process was derived from the point of view of free energy. Several systems were used to illustrate chemical equilibrium. The solubility of oxygen in water (15) was shown to lead to an equilibrium constant. The synthesis of ammonia was discussed in some detail as a typical equilibrium and also to provide a basis for discussion of the problem of nitrates in agricultural water. Some students-commented that this discussion was valuable because tertiary treatments of water are just beginning to be operative. Next the combustion of carbon, nitrogen and sulfur were presented with for example S03/SOz ratios computed at various temperatures in air. It was gratifying to the students to see that a t 100O0C,the S03/S02 ratio is calculated as about 0.05, consistent with the 0.02-0.03 ratio actually observed, while a t 2 5 T , the ratio becomes large, consistent with the observed conversion of SO2 in the atmosphere. The thermodynamics of some of the proposed conversion processes (6) was also examined. Ionic equilibrium was introduced by first discussing some practical ways to shift equilibria in solution (4), and the solubility of A ~ ( O H ) Jand Fe(OH)2, used as water coagulants, was then calculated as a function of pH. The topic of acid-base equilibria was illustrated by consideration of the activated sludge process (4) for sewage treatment, where the carhonate-bicarbonate buffer system is important. It was shown how the system no longer functions if the acid concentration becomes too high. The students had seen a sewage treatment plant but they were unaware of the chemical principles involved. Next, the problem of hardness in water was examined by computing solubilities of limestone in the presence and absence of
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/Journal of Chemical Education
carbon dioxide, and the results were related to the calcium contents of natural rivers and lakes. Complex ion equilibria were introduced through the observation (16) that more mercury dissolves in salt water than in pure water, and i t was shown that the solubility of HgClz in salt water is 45 times its solubility in pure water, in agreement with the observed 50-60 times for NaCl of the same concentration. Finally, the problem of treatment of cyanide-containing wastes containing transition metal ions was considered to show the necessity of destroying the cyanide ion before removing the metal ions was attempted. Ideally, a t least the topics of electrochemistry and kinetics should be discussed in a course of this sort, and plans are being made to incorporate these topics next year. The approach outlined above will still be used, that is, to present up-to-date examples of the application of physical chemistry to environmental problems, while using a good fundamental texthook for developing the basic ideas. Student reaction to this approach was uniformly enthusiastic, because they felt there was a dialog between them and the instructors. Several students commented that they now saw how to apply thermodynamics to environmental problems involving chemical reactions, and they understood the fundamentals of thermodynamics better. One student reported that he had been apprehensive about taking another chemistry course at first, but now if he needed more chemistry, he had confidence in his ahility to understand the subject. Also several students said that they had a much clearer idea about their senior research projects in Civil Engineering after they finished the course. The instructors found the course challenging, that is, to find and to present the current state of the art and to relate this to fundamental principles was satisfying. Persons who wish to try this approach to teaching physical chemistry for environmental engineering students are invited to correspond with the authors. Literature Cited (11 Miller. G. Tyler Jr.. "Energetin, Kineties and Life." Wadsworth Publishing Co., Inc.,Belmonl. CsMornia, 1971. (2) Crockford. H. D. and Knight. Samuel B.. 'Tundammtals of Physical Chemistw.Semnd Edition, John Wiley& Sona. Inc. NevYork, 1967. (3) SLsrr. Chauncey. Sei. Amer., 224 131.36 (1971). (4 S~svyar.Ciair N. end McCsrty, Peny L., "Chemistry for Sanitary Engineers" (2nd Ed.), McGraw-HillBook Co..lne., NeuYork. 1967. ( 5 ) Hodges, Laurenf. "Lacture N o t e in Environmental Pollution." Phyrien Depf.. lows SfateUniv.. Amos, Iowa, 1970.p. 46. (61 Berry. R.S.andLehman, P.A.,Ann. Rsu. P h p . Chrm.. 22,17 (19711. (7) Baas, David E. andCarraher, ChsrlesE. h.,J. CHEM.EDUC., 49, 112(1972). (81 Stevenson. P. E , d . CHEM. EDUC., 17.272(1970). 191 Msgill, Paul L., Holden, Francis R. end Ackley, Charles. Editors. "Air Pollution Handbook."McCraw~Hill Book Co., h c . , New York, 1956. 1101 bates, DavidD., SCL Amcr.. 225 (31.88 (1971). I l l ) Bent. Henry A . J . CHEM. EDUC.,48,692l19711. 1121 Margaria. Rudolfo. Sci. Amer.. 226 131.84 ( p 7 2 ) . I131 Tucker, Vance. Sci. Arne,.. 220ii1.70(1969). (141 Delwiche.C.C..Sci.Arnsr., 225(31, 136l1970). (151 Barron. Gordon M.. "General Chemistry." Wadrwarfh Publishing Co., Ine.. Belmont. California, 1912. (16) Perisic, M.and Cuenod,M.,Scienc~.175.142 119721.
