Chemical Energetics

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Chemical Energetics
All about enthalpy, calorimetry and the First Law of Thermodynamics A Chem1 Reference Text
Stephen K. Lower • Simon Fraser University1

Contents
Part 1: Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Part 2: Basic thermodynamics: what you need to know . . . . . . . . . . . . . . . . . . 5 Systems and surroundings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Properties and the state of a system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Heat and work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Internal energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 The First Law of thermodynamics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Pressure-volume work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Adiabatic and isothermal processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Reversible processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Part 3: Heat changes at constant pressure: the enthalpy . . . . . . . . . . . . . . . . 11 The heat capacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Part 4: Molecules as energy carriers and converters . . . . . . . . . . . . . . . . . . . . 13 Chemical Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 How molecules take up thermal energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Part 5: Energetics of chemical reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Changes in enthalpy and internal energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Variation of the enthalpy with temperature . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Part 6: Thermochemistry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Thermochemical equations and standard states . . . . . . . . . . . . . . . . . . . . . . . 18 Enthalpy of formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Hess’ law and thermochemical calculations . . . . . . . . . . . . . . . . . . . . . . . . . 20 Calorimetry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Part 7: Some applications of First-law-related topics . . . . . . . . . . . . . . . . . . . . 25 Enthalpy diagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Bond enthalpies and bond energies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Energy content of fuels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 Energy content of foods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 Thermodynamics and the weather . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

1. To contact the author, please use the Web form at http://www.chem1.com/VT_mail.html

The Chem1 Virtual Textbook is a collection of reference textbook chapters and tutorial units providing in-depth coverage of topics in college-level General
Chemistry.

For a more information on the Virtual Textbook contents, see http://www.chem1.com/acad/webtext/virtualtextbook.html

This document covers the basics of chemical thermodynamics, the First Law, and thermochemistry at a level appropriate for first-year college chemistry. It was last modified on 23 December 2003 . It can be downloaded from http://www.chem1.com/acad/pdf/energetics.pdf A Web-based version is available at http://www.chem1.com/acad/webtext/energetics/

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All chemical changes are accompanied by the absorption or...
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