ROBERT C. PLUMB
chemical principles exemplified
Worcester Polytechnic Infitute Worcester, Massachuseth 01609
Culture and the Conservation Laws lllustroting elementary applications o f the basic tenets of ofomic theory ond thermodynamics t o the problem of environmentol pollution and survivol o f the species
Contribution by Professor Henry A. Bent North Carolina State University Many-possibly most-of the larger problems of society (peace, poverty, prejudice, population, pollution) are closely related to the question: To what extent can we manipulate our environment-our physical, biological, and cultural environments? One finds part of the answer in the conservation principles of physical science. Most urban dwellers are aware, consciously or unconsciously, that what goes into a city (in trucks, trains, and planes) must go out (in the air, rivers, and barges), or pile up (in litter, private cans, and public dumps). There are n o consumers of mass or energy, only converters. We may try to dispose of our waste beer cans, e.g., by burying them (thereby polluting, eventually, our ground water), or by burning them (if combustible, polluting our air), or by flushing them down the drain (if soluble, polluting our streams and rivers). Rut we cannot annihilate beer cans. "Burn up," "waste disposal," and "consumer economy" are misleading phrases. We may destroy the form but not the su6stance of our physical surroundings. In all chemical and physical transformations, matter, according to Dalton, is conserved, atom for atom.
technological procedure in order to slow down the catabolic process and keep some foods fresh for the consumer. This is known as controlled atmosphere storage. I n pioneer days, apples and cabbages were buried in barrels to preserve them through the winter. I n our age, many warehouses for apples and tomatoes use controlled atmosphere. How does it work? Glucose, as an example, degrades through a series of enzyme activated steps to pyruvic acid, a process called glycolysis, and in one of the last steps molecular oxygen is required. This reaction wit.h oxygen takes place in the mitochondria, the "powerhouses of the cell," shown in the adjoining figure. To get there, molecular oxygen must dissolve in the cytoplasm and diffuse through the mitochondria wall. The supply of molecular oxygen required to carry out the glycolysis reaction can be cut off by reducing the concentration of dissolved oxygen, and this is determined by a simple equilibrium with the gaseous oxygen. Reducing the partial pressure of oxygen will cause the flow of material in the catabolic process to stop, just as too few attendants dispensing toll cards will cause trafficto pile up at a toll road check point. In practice there are other complications and alternative catabolic pathways, so that oxygen cannot be entirely removed and carbon dioxide needs to be controlled. However, oxygen contents of 2% and carbon dioxide contents of 5% permit storage for several months longer than normal. Instant First Aid
Prolonging Death (in Apples)
Illustrating principles of thermochemistry
lllustroting principles of chemical equilibrium ond kinetics
Contribution by James A. K a u f m a n Worcester Polytechnic Institute
When an apple or tomato or strawberry is picked for the market, man imposes a dramatic change on the way of life of the biological cells of which the fruit is composed. The cells go on living but the metabolism shifts from anabolism, in which various chemical building blocks, cellular constituents, are being formed and stored, to catabolism in which the stored cellular constituents are consumed in order to keep the cell alive. After a time the fruit is worthless to the consumer because the cells have themselves consumed a large part of those chemicals such as fruit sugars which humans relish, and eventually even the life processes in the cells are brought to a halt. An elementary principle of chemical equilibrium bas been used in the form of empirical black art for centuries and in recent years as an increasingly important 518
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Journal of Chemical Education
A student learns that the heat of solution of a salt in water can be either positive or negative, but to whom does it matter? One needs only to look as far as the nearest dispensary or school athletic department to find a direct practical use of the effect: instant ice packs or hot packs for use when refrigerators and hot water aren't available! How do they work? AH.,, of NH4N03 is -6.3 kcal/mole and the solubility is 118 g/100ml of H20 at 0°C. Place a quantity of NH,N03(s) in a small, thinwalled plastic bag and seal it, together with water, inside a tough flexible plastic bag. When a sprain or other such injury occurs, break the small bag by kneading the large bag and you have an "ice pack." How cold will it get?
