Tiêu đề Exercise 5 Prelab Study Guide.pdf ✅

CHEM 111.1 Physical Chemistry I Laboratory No part of this module may be reprinted without the written permission of the Physical, Inorganic and Industrial Chemistry Division, Institute of Chemistry, UPLB, College, Laguna. 1 Module 7 Prelab Study Guide ENERGIES OF REACTIONS I. OBJECTIVES At the end of the module the students should be able to: 1. create molecular structures of the species involved in the reaction between ethene and propane producing ethane and propene using Avogadro; 2. generate input files for geometry optimization; 3. optimize the structures using GAMESS; 4. use the optimized structures as inputs in calculating absolute enthalpies using GAMESS; 5. calculate the enthalpy of the reaction; and 6. compare the calculated value with the literature experimental values. II. INTRODUCTION The change in enthalpy associated with a chemical reaction is called the enthalpy of a reaction (∆rH). It is the difference between the enthalpies, H of the reactants and products in the balanced equation, with ν as the stoichiometric coefficient. ∆rH= ΣνH (products)-ΣνH (reactants) (7-1) Enthalpies of reactions are determined using the enthalpies of formation of the reactants and products from their component elements. So, equation 1 becomes: ∆rH= Σν∆fH (products) -Σν∆fH (reactants) (7-2) which has been the equation used for calculating enthalpies of reactions. However, with the advancements in the field of computational chemistry, the determination of total energies are made possible. In this module, we will use: 1. General Atomic and Molecular Electronic Structure System (GAMESS) is a software that allows a wide range of computational chemistry calculations. It is a general ab initio quantum chemistry package maintained by the Gordon research group at Iowa State University. 2. Avogadro is a molecular builder/editor and visualization tool that has a lot of applications in computational chemistry. These two open-source programs are commonly used hand-in-hand for energy calculations which can then be used to calculate enthalpies of reactions. One of the simplest reactions that would yield a fast and accurate result in computational studies is the reaction between ethene and propane, producing ethane and propene. This is an example of an isodesmic reaction wherein the number and type of bonds in the reactants and products are conserved.