1. Two of the most dangerous pollutants in the exhaust from automobiles are nitric oxide (NO) and carbon monoxide (CO). In the presence of a Monel (a nickel-copper alloy) catalyst, the concentrations of these gases are reduced by the following equilibrium process:
The equilibrium constants vary with temperature as follows:
2. A proposed method for collecting solar energy involves the equilibrium process:
The sulfur trioxide is heated in a chamber to 800 įC by solar energy. The sulfur dioxide and oxygen are then transported to a low-temperature heat exchanger where they recombine to form sulfur trioxide and liberate heat. At 800 įC, sulfur trioxide is 56% dissociated when the total pressure is 3.00 atm or 304 kPa. K p is 1.05 atm or 1.07 X 10 5 Pa or 1.07 X 10 2 kPa.
3. K sp (solubility product constant), K a (dissociation constant for acids), K b (dissociation constant for bases), and K f (formation constant for species, such as FeSCN 2+ in this module’s Laboratory Activity 1 ).
BETWEEN CHEMISTRY AND OTHER DISCIPLINES
1. Chemical processing plants, such as oil refineries and chemical manufacturing plants, work with chemical reactions that establish dynamic equilibrium. It is often true that much creative energy is expended to determine how to shift the equilibrium so that the desired product is produced in large quantity and at a reasonable cost. A good example of this problem is the synthesis of ammonia from the elements, according to the equation:
N 2 (g) + 3H 2 (g) 2NH 3 (g)
2. Stalactite/stalagmite growth is based on equilibrium involving calcium carbonate and carbonic acid. See the article in ChemMatters by David Tanis (February 1984, pp. 10-11, “Underground Sculpture”).
TO THE CONTEMPORARY WORLD
1. The problem of the relationship between eating sugar and tooth decay should interest most students. Fermentation of sugar in the mouth involves an increase in H + concentration. Over a period of time, such as a night’s sleep, increasing H + can shift the equilibrium between tooth enamel and the ions making up the enamel to the ion side of the reaction. The equilibrium is:
Ca 5 (PO 4 ) 3 OH(s) 5Ca 2+ (aq) + OH (aq) + 3PO 4 3 (aq)
Tooth enamel Stress is put on this equilibrium by formation of HOH (H 2 O) and/or HPO 4 2 , causing a net loss of solid enamel.
2. Carbon monoxide, a by-product of “incomplete” oxidation (burning) of hydrocarbons, poses a major pollution problem. It is dangerous to life because it binds to hemoglobin and therefore excludes oxygen. Hemoglobin is a complex molecule that transports oxygen in the blood system.
The binding process can be represented by the equilibrium:
Because of a balance between the forward and reverse reactions, oxygen can be released where it is needed in the body. However, CO can also bind to hemoglobin:
This equilibrium has a greater K eq than the hemoglobinO 2 reaction. Consequently the hemoglobin is not available to transport oxygen. The victim of CO poisoning suffocates.
3. Ozone in our upper atmosphere absorbs ultraviolet light from the sun according to the equilibrium:
The reverse action regenerates O 3 , which can absorb more ultraviolet light. Chlorofluorocarbons have been used in aerosols and refrigerants. These substances can release chlorine radicals that destroy O 3 irreversibly. Scientists are concerned that increased levels of chlorofluorocarbons will migrate into the upper atmosphere and deplete the ozone supply, allowing larger quantities of potentially harmful ultraviolet radiation to penetrate to the earth’s surface.
1. Field trips. Control of equilibrium is a theme in many industrial processes. A visit to a local chemical industry might be a useful activity, although equilibrium probably should not be the only reason for the visit.
2. Knowledgeable individuals : industrial chemists, university chemists, physicians, and pharmacists
A visit to a chemical plant to see the contrast between laboratory-based chemistry and scaled-up chemistry might be useful. Again, the direct association with equilibrium is not the sole reason for such a visit.
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