JOHNJ. ALEXANDER University of Cincinnati Cincinnati, Ohio 45221
exam que~tion exchange Physical Chemistry-Thermodynamics
4) (a) 5) (c) Change the word solute to soluent. R a )- , ...I l~
Jack Richlin Monrnouth College West Long Branch, NJ 07764
7) tb) A low-hdng iurutrupc will hc prduced unly when the vapor pressurc ofrhe sdutim is higher than the vapor pressures of huth
One difficulty found in testing in physical chemistry courses is that the goal of assessment of understanding of the theoretical material often involves evaluation of derivations and manipulations of memorized equations. Additionally, working out of problems and derivations can take time, so the scope of material the instructor can reasonablv cover in a 50-minute exam is necessarily limited. It then follo& that the point value for each auestion must he inflated in order that the student be assured there is sufficient time allotted to think through each ouestion and search for the Droner ~ n r o a c hand crucial . a .. assumption or condition. Assignment of ~ a r t i a~l o i nvalues t for each answer is difficult for the instructor because if the student misses the initial thrust of the auestion. hwshe will often fill the space with false starts whichehow some understanding and-leave the instructor with the lingering feeling that the student was on the right track but simply did not recognize the critical point. The style of question herein presented allows the instructor to cover a wide range of material a t varying achievement levels in a reasonable period of time. I t is particularly suited for testing in thermodynamics, and the questions can be arranged to test for basic understanding, subtle points, or rote memory. Normally, questions of this type would constitute approximatefy 50 percent of an examination, the other half being given over to traditional-style problems. Below are examples of subject matter and degree of sophistication for which this format may be used profitably. Quesilon State whether the followine are (a) absolutelv true. (b) conditionally true, or ( c ) absol&ly fake. If your &wcr is (hl, eive the conditiun(s1 which make it true. If vour answer is (cl, substitute, if possible, a correct statementfor the situation.
1) A system gains in heat, q, when it expands isothermally. 2) The van der Waals' constant,. a,. corrects for the excluded volume of the gas molecules. dSSrJt = dq1T. ' (If V is a function of T and p , then ( a T l a p ) I~=& ~P)T(~TI~v),. At the boiling point of a solution, the chemical potential of the solute in the liquid phase is equal to the chemical notential of the solvent in the vaoor . .~ h a s e . 6) ~~(GIT)I~T],, 7 -HIT2. 7) Positive devlat~onfrom Raoult's law in a binarv solution produces a low-boiling azeotrope. 8) From d U = -pdV TdS, we get the Maxwell relation ( a p l a ~=) -(asiav),. ~ 9) pliquid < paolid for a pure substance a t a constant pressure. 10) AG = J - S d T .
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Acceptable Solution 1) (h) The external pressure must he greater than zero. (a) is acceptable at the junior level. 2) (c) The constant, b, corrects for excluded volume. 3) (b) True when the process is reversible (dq = dq,,).
pure components at that temperature. 8) (c) (Jp1JS)v = -(JTlJV)s. 9) (h) True when T > Tr.*,. 10) (h) True when the process is carried out at constant pressure.
Superfluous Steps in Glycolysis? Thomas P. Chirpich Memphis State University Memphis. TN 38152 Students encounter the glycolytic pathway in detail in biochemistry but may also have had previous encounters with it in a physiology or a bacteriology course. Too often they feel that there is not much more to he learned and regard the pathway only as a series of steps to be learned by rote. The followine auestion shows that there is much more to the pathwa
