JOURNRL OF
Chemical € ducation: Software Abstracts for Volume 6B, Number 2 KinWORKS: A Learning Tool for Kinetics Lab Richard W. Rarnette ~ a r k o College n Northfiled, MN 55057
KinWORKS is a computer simulation that is designed to help students learn how to design chemical kinetics experiments, collect and analyze kinetic data, and draw conclusions from those data. I t offers a large number of reactions of graded complexity to investigate. provides far the instructor to make unique assignments for each student, including assignments where the solutions are not revealed. Solutions to these reactions can he revealed thmugh use of an auxiliary program. reouires the student to desien even, exveriment to ahtain time and wncentrstux data. 'I'hls mvnl\~esselectwn of ternprmtLre, ingttnl concentrations, whether to use rhe ~ n l c k ~ u t t drare law mrthod or m>rlal rare* mrthwl, and when the data points are taken as the reaction progresses. imposes experimental error on all data, which results in a data-quality penalty for poorly designed experiments. Examples are inadequate flooding, failure to let the reaction progress far enough for integrated rate law work, or attempting to deduce the activation energy by using a temperature range that is toa small. includes convenient high-resolution platting. Any or all reaetant concentrations from the data sets may he plotted versus time a s either concentration, reciprocal concentration, or natural logarithm of concentration. Aleast squares fit of the data is shown with each plat. nermits simulation of realistic data far a known reaction
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printed problems based on actual reactions. permits graphical analysis of externally prepared data, such as actual laboratory data, literature data, or textbook pmblems. This feature includes time and concentration data, which can he plotted as described above, and temperature and rate constant data. which can he dotted in wavs . aovra., prrate to drrerminmy ;he ncrivauun i n e r g \ . Such dotn can br enrrrrd dmrtly into KmWORKS or retnevrd from files prepared by a text editor. provides an efficient, friendly interface with both keyboard and mouse support that makes it easy to carry out a number of experiments in a short time and safeguards against user averation errors. .offers on-screen helpon kinetics principles and experimental strategy, with calculation examples.
KinWORKS organizes reactions into three levels of stoichiometric complexity: easiest
A hardest
+ ... + bB pP+ ... + bB + eC + pP+ . .
A +pP A
where b, c and p are integer stoichiornetric coefficients. Each reaction is given a unlaue set of characteristics. The stoichiometrie co&icients are known, but not the rate constant, activation energy, or the reaction orders. KinWORICS sets up a standard type of rate law for each reaction: 762
Journal of Chemical Education
rate = 4 I A l l d t = dlPllpdt = k LAI*IBt"IClZ
Generally, the orders for reactants x, y, and z may be 0,1 or 2. However, experienced users can challenge themselves with problems where z may be from -2 to +2 and may be fractional.
Quantum Barrier David A. Lloyd
Hofstra University Hempstead, NY 11550 The interaction of a quantum mechanical particle with a ~otentialenerw barrier illustrates a number of interesting aspects of quantum behavior, the best known of which is tunneling. This problem has been treated in quantum mechanics texts by Pilar (l),Atkins(Z),Davis (31,and Powell and Craseman (4).There is excellent software by Rioux ( 5 ) available for many bound-state quantum mechanics problems, hut it does not include the barrier problem. Quantum Barrier allows students to interactively discover the effect of particle energy, particle current, barrier height, and bamer thickness on the reflection and transmission coefficients.At the same time the wave function for the particle beam is displayed. The Quantum Bamer display screen consists of three panels. The lower, or control panel, allows the student to try particle energies up to 1000 eV in 1%increments, and barrier energies up to 400 eV in 5% increments. Thus, the ratio of particle energy to bamer height can be adjusted from 0.025 to 50. The barrier width can be changed from 0.2 to 2.0 Angstrom units, and the particle beam current is
adjustable in 1%increments to 1000 mA. I n all cases, the mass of the particle is assumed to be the electron rest mass. The use of experimental a s opposed to atomic units is intended to eive the student an intuitive feeling for the quantitiesinvolved. The center panel depicts the physical situation, using differently colored pixels to represent incident particles a s opposed to reflected particles. The speed a t which the pixels move across the screen is made aporoximatelv to the velocities of the parti"proportional .. h e s they represent. The detector icon in the ;enter panel displays the magnitude of the transmitted current, while the wave function is simultaneously displayed in the upper panel. The imaginarycomponent of the wave function is represented by the thickness of the line drawn on the screen, which allows the phase of the function to be visualized. Quantum Barrier can be used to explore one or more of the followine assienments: Plot the increase in transmis-" sion a s the particle energy appmaches the barrier height. What is the period of the cvclic variation in reflection a t particle energies in excess of the barrier energy? How does the phase of the wave function change a s the amount of reflection changes? Is transmission more sensitive to barrier height or barrier width? Why does the number of partitles in the display decrease with increasing particle-energy a t constant current?
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Animated Demonstrations II: Mass Spectrometer; Single-Crystal X-Ray Diffraction Philio . ..... I. PavlikNonnern M c y a n L n verstry Marq-ene, M 49855-53343
Thcse two prokwuns continue n series ol'animated demonstrations ~ u b l i i h r dcarlicr 16,. Muss Spectmmeter provides a n &mated view of the workings bf a simple mass spectrometer. A lecturer or student may select one of several different elements and generate its mass spectrum. Peaks appear on a chart and isotopic masses and abundances are reported in a table. Single-Crystal X-ray Diffraction shows a n X-ray source, a n animated beam of Xrays, a rotating single crystal, and a film on which spots are produced by diffraction of the beam.
About This Issue John W. Moore and Jon L. Holmes University of Wisconsin-Madison Madison. WI 53706-1396 Chemistry textbooks typically present kinetics problems of onlv a few tvoes: a table of time and concentration data for a unimolecular reaction; a table of initial rates corre" A
sponding to a few different combinations of reactant concentrations; or a table of rate constants a t two or more temperatures. Students are asked to deduce orders, rate con. problems are of stants. and activation e n e r ~ e s Such necessity "final data", and preempt the student's grasp of what had to be done in the lab to obtain the numbers. KinWORKS provides an excellent alternative, allowing students to explore a wide variety of different experimental situations much more rapidly than they could in the lab. Q.uantum Barrier addresses the problem of insufficient lecture time to explore the quantum-mechanical model of electron tunneling in detail. Often only the final expressions for the reflection and transmission coefficients are presented. The expressions for the wave functions are not so easily visualized as those for the particle in a box, and the algebra needed to obtain them is extremely laborious. Given these obstacles, few students are likely to investigate the properties of the model on their own. By allowing the student to interactively discover the various properties of quantum barriers, this program opens a much wider range of experience and intuition. Short but graphic, animated demonstrations can spice up any lecture. They are also useful for students to explore more fully on their own after a lecture is over. Mass Spectrometer will be useful when the ideas of separating isotopes and determining isotopic masses are presented. Single-Crystal X-Ray Diffraction allows students to see the basic components of an X-ray diffraction experiment and to envision how a beam of X-rays is diffracted by a crystal. Hardware Requirements Programs in this issue of JCE: Software are designed for IBM PSl2, PC, or PC-compatible microcomputers with 640K of RAM and one floppy disk drive. VGA or compatible graphics and PC- or MS-DOS 3.1 or later are also required. (CGA and EGA graphics will not work.) A disk drive larger than 360K is recommended for KinWORKS. Literature Cited 1.Pilar. F.L. Elsrnmrow Quantum Mechonles, 2nd ed.: McGraw-Hill: NewYork, 1990, pp. 73-77. 2. Atkins, E W. Molecular QuonfarnMmhmnics, 2nd ed.: Oxford Univereity Press: New York, 1983,pp. 4 1 4 . 3. Dan$,Jr., J. C. A d u o n d Physic01 Chamlsin: Ronald Ress: New York, 1965. pp. 88-43. 4. Powell, J.L.; Crasemsn. B. QvoniumMechonics, Addison-Wesley:Reading,MA.1961, pp. 107-109. 5. Rioux, F. "Numerical Solutions for Schradingeri Equation"; J. Chem. Edur: So,% wore, 19901IIB 12). 6. Pav1ik.P. 1. J Chem. Educ:Softwam 1992 58(21.
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Volume 70 Number 9 Se~tember1993
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