JOSEPH
from the pa~t
Edited by: S. SCHMUCKLER
Chairman of Science Education Temple University 345 Riner Hall Philadelphia, PA 19122
Reaction Rate
Catalysis
T h e r a t e of a reaction approximately doubles for a t e n degree temperature rise, T r u e or False? J. E. House, Jr., responded t o this "Chemical Querie" i n J. CHEM. EDUC.46, 674-675, October 1969.
"Catalysis," Doris Kolb, J. CHEM. EDUC., 56,743-747, November 1979. Many thousands of examples af reactions being accelerated by addition of another substance can be shown, but the phenomena of catalysis is still not completely understood. Kolb's treatment of the topic of "catalysis" in her feature article, "Chemical Principles Revisited," is easy tu read, interesting, and complete. Following an introduction of "What is a Catalyst?" she presents a brief history dating back to Brezelius'and Ostwald's work. Further subtopics include affects of catalysts on rates of reaction, the eatalytics process, enzymes, and industrial catalysts. She ends her article by saying ". . .yet catalysis in many ways is. . .much more an industrial art than an academic science." "These compounds should show strong attraction, but when they are mixed-no reaction. They seem in a state of paralysis. Then, touched by some curious rubble, they suddenly darken and bubble! The magic is known as catalysis."
". . .whether or not the rate of a reaction is doubled by an increase of 10' depends upon the activation energy of the reaction and upon the range of temperatures where the 10" interval falls."
The Law of Mass Action "The Law of Mass Action,"Steven Berline, Clark Bricker, J. CHEM. EDUC., 46,499-501 August 1969.
by changes in temperature, changes in pressure, and changes in the concentration of reactants and products. When mare quantitative aspects of equilibria are approached, the idea of an equilibrium constant is introduced and methods to evaluate these constants are disthis method, it is necessary to understand that mast chemical reactions do not proceed by the mechanism suggested by the balanced equation far the overall reactian. Instead, several sequential steps may be involved, and the balanced equation for the overall reaction is merely the sum of the balanced equations for each of thesteps. A reaction consisting of two or mare steps cannot proceed any faster than the slowest or rate-determining step. In the derivation of an equilibrium constant from kinetic data it is essential to know how the rate determining step is affected by the concentratian of reactants and, similarly, how the rate of the reverse reaction is affected by the concentration of products. The Law of Mass Action, proposed by Guldberg and Waage in 1867, states that the rate of the forward reactian is proportional to the product of the concentrations of the reactants, each raised to the power of its coefficient in the balanced equation. Thus, if the rate-determining step for areaction is represented by xA+yB=C we would write Rate of forward reaction
= a[A]z[B],
A Versatile QuantitativeExperiment "The Effects of Chloride Ion a n d Temperature on Lead Chloride Solubility," Allen C. West, J. CHEM. EDUC., 46, 773-775, November 1969. "This experiment is based on a simple accurate volumetric method. By using all the student results a significant amount of data can he collected in a short time. The lead chloride system lends itself to study and interpretation a t several levels of sophistication, so that the experiment can be adapted to the background of the students and the time available. I t demonstrates some of the false simplifications involved in a rudimentary treatment of solubility equilibria and the common ion effect, and it can also be made openended in a variety of ways."
Demonstration/Experiment I n t h e March 1982 edition of this column, J. R a e Schwenck's "Chemistry of Silver," J. CHEM. EDUC., 36,45, January 1959, was cited. Another similar article appeared t h a t opens u p some interesting student experiments and/or classroom demonstrations. "A Simple Demonstration of Some Precipitation and Solubility Effects," E . Matijevic, J. P. Kratohvil, M. Kerker, J. CHEM. EDUC., 38,397-399, August 1961. The writers have developed avery simple yet striking experiment which demonstrates a number of ". . . precipitation and complex solubility effects." The purpose of this paper is to describe this experiment and to provide~anexplanation of the basic physical process involved. Using a silver bromide system the writers present data, eranhs, and tables that are useful for both teacher and student to inderstand the observable phenomena
The reason for this relationship is usually left unexplained. Indeed, the student often gains the impression that the parameters in [AIs[B]Y are determined solelv bv exneriment and that it is onlv bv coincidence that they are the sameas the coefficients of the reactanis in the balanced equation. In more advanced chemistry courses, the proof of the Law of Mass Action is based on chemical potentials. This approach, however, is not well suited for elementary courses. I t is the purpose of thm paper to present a derivation which should have meaning and could be utilized at an elementary level." The derivation nresented hv Berline and Bricker takes the reader steo bv steo through a series of eauationr that are exolicit. T h e au-
"Sickle-Cell Anemia. Hemoelohin Solubilitv. a n d Resistance t o Malaria," avid'^. arti in, J a m e s ~ u h e e y J. , CHFM. EDUC., 49,177-178, March 1972.
that their approach is in agrekment with the Law of Mass Action, and why the agreement exists
This article provides a wealthof resource material far the teacher who wishes to use sickle-cell anemia to illustrate the relevance of chemical principles, in this case, solubility.
Interdisciplinary Application of Solubility
Volume GO
Number 5
May 1983
417
