JOURNRL OF
Chemical € ducation: Software Abstracts for Volume ID, Number 1 AnswerSheets
Signif~cantFigures Temperature Conversion Stoichimetry 'VSEPR Structures
Richard Cornelius Lebanon Va ey Col ege Annvl e. PA 17003-0501 The series of software modules called AnswerSheets is a collection of files for Microsoft's spreadsheet program Excel. The user interface is through dialog boxes, buttons, and pull-down menus; no knowledge of spreadsheets is necessary in order to run the software. The primary focus ofAnswerSheets is to provide answers and explanations to problems that students provide. Modules are available to handle topics a s varied a s unit conversion, inorganic nomenclature, stoichiometry, and VSEPR structures. The problems that a student provides can come from a textbook, homework, an exam, or any other source. Resources available to help a student include a calculator that understands chemical formulas, a glossary, and a periodic table for access to data about the elements. If a student wants practice problems, AnswerSheets can serve as a nearly limitless source, and it provides answers and explanations to the problems it generates. An additional feature is that each module provides a capsule summary of the topic. The
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ease of copying questions and answers from AnswerSheets into a word processor also makes the software helpful in the preparation of quizzes, complete with an answer key. The modules included in this issue are
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Screen from AnswerSheets.
:reen from the Molecular Dynamics Simulator.
Molecular Dynamics Simulator G. Peter Matthews Polytechnic South West Plymouth, England Emerson F. Heald Thiel College Greenville, PA 16125 Molecular Dynamics Simulator provides a display ofmolecular motion in a solid, liquid, or gas. An updated version of the program described by Matthews (11,i t shows nonpolar molecules moving under the influence of the LennardJones S 1 2 potential function. Initially, a small sample of 32 molecules is placed in a cubic lattice. The molecules are assigned random velocities and inhabit a cubic section of three-dimensional mace that repeats itself over and over in each direction. A periodic boundary condition applies-if a molecule leaves through the one side of the c&e, i t appears on the opposite size. The molecules interacting with a given molecule are its closest neighbors, including ones in neighboring cubes. The user supplies values of the temperature and number density, or number of molecules per-unit volume. One of three things happens as the calculation proceeds: A t low temperatures and high densities, the molecules are so close to one another that they remain in the solid structure. The molecules move around their equilibrium positions in the lattice, but they cannot move past one another. 'At high temperatures and low densities, the molecules are far enough apart that intermolecular forces are negligible. In this ease thev move in straight lines. If two molecules anpmnch, they are first attranpd and then repelled. simul&mg a mllwinn. After a while all memory of [he original solid is l o ~ nt n d the n~ulreuleshehnve as if they are in a gns. .At intermediate temperatures and densities, the molecules are far enough apart to be able ta move past each other but close enough that they are continually attracted and revelled by each other. In this ease the molecules move in random curved trajectories and their behavior simulates that of a liquid. The sample of molecules is too small to simulate the behavior of a multiphase system, but users can clearly see how molecular motion differs in solid, liquid, and gas states. provided bv the pmeram is a view of the cube The display . .. from one side. ~olecul&motibncan be observed either as tracks (lines tracing the position of the centers of the molecules) showing w h e r e t h e molecules have been or a s spheres (circles) having the collision diameters of the molecules. The spheres move and leave shadows showing where they have been.
Volume 70 Number 5 May 1993
387
