edited by: RON DELORENZO Middle Georgia Cdlege Cochran. Georgia 31014
Weight-Loss Diets and the Law of Conservation of Energy
Chemical Wastes and the Law of Conservation of Matter
John W. Hill University of Wisconsin-Rlvw Falls River Falls. WI 54022
John W. Hill
An important chemical principle with interesting applications is the law of conservation of energy. If energy is conserved, why do we have an energy crisis? Some of us have a personal energy crisis. We eat so much food and exercise so little that the excess energy taken in is stored in fat deposits for possihle future use. Energy is conserved. The law nf conservation of energy is also of intrrest to those who diet to lose weight. There are dozens of books with "maeic" methods for losing weight. ( ~ o n e yis also conserved: ~ r , l l & gained by the auacks e u u a l dollars lost hv the suckers.) All weieht-1% diets kork if ( A d only if) the c&ic intake isless than the calories burned. Is exercise a good way to lose weight? Consider taking off a kilogram of fat.'
Matter cannot be destroyed, but it can be changed from one form to another. That's what chemistry is ahout-transformations of matter. Nearly any general chemistry student can correctly state the law of conservation of matter in one form or another. The enlightened students will realize that this law is the basis for calculations involving chemical equations (stoichiometry). Atoms are conserved; the law is well established and widely known, yet we hear scientists and engineers talk about getting rid of wastes as if matter could simply be obliterated. I t cannot; certainly not in meaningful amounts. If we have waste--chemical or nuclear or agricultural or whatever-there are only three places to put it-in the air, the water, or the land. I t is possible to change matter, in some cases, to a less harmful form. For example, we do not have to dump polychlorinated biphenyls (PCBs) on the ground or into the waters. They can he incinerated. Properly done, this transforms the PCBs into carbon dioxide, water, and hydrogen chloride (HCI). These are presumably less harmful forms of matterunless you live downwind, in which case you might wonder about the HCI from the improper disposal of incineration products. Mercury is an element. I t is toxic as the free metal and in all soluble combined forms. For vears it was thoueht that mercury in the mrironment was no prohlem; it wuuld be ronverrnl h\. nature t insoluble. harmless merrurs(I1)sullidc. Then we learned that certain bacteria can convert kercury compounds to extremely toxic methvlmercw which is readilv taken up by organisms: Chemists are not thk only organismi that can carry out chemical conversion. Atoms are conserved. Present day detergents are hiodegradable. But what do they degrade to? They cannot degrade to nothingness. Remember-matter is conserved. Barry Commoner claims that degradation leads to toxic phenol. Whether he is correct or not, the situation does lend credence to the old adage, "out of sight, out of mind." Our rivers no longer foam, so we assume the detergent problem has been
University of Wisconsin-River Falls River Falls. WI 54022
1kg fat = 7700 kcal(32 000 kJ)
Let's do it bv runnine. Runnine a t a moderate Dace (about 5 minlkm) expends energy at a ;ate of about 95'kcal/km (400 kJ/km). How far would wr have to run to l~urnoffa kilorram of fat? 1km 7700 kcal X -= 81 km 95 kcal That's about the distance of two marathons! And without any food taken in! Yet vuu read advertisements which feature diets promising weigh
