Bond Enthalpies and Exothermic or Endothermic Reactions
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Endothermic Reaction Solid barium hydroxide octahydrate (Ba(OH)2*8H2O) and ammonium thiocyanate (NH4SCN) are mixed in a beaker, which is then placed on a few drops of water on a small board. The reaction that occurs is highly endothermic.
Calorimetry / Thermochemistry |
Thermodynamics
Entropy These processes are shown in reverse. The situations shown are so highly improbable that we would not expect to observe them in nature.
Thermodynamics : CompareEntropyQual (16 Variations) Indicate which substance in each of the following pairs of substances you expect to have higher entropy. Assume that you have a mole of each substance and all substances are at the same temperature.
Appreciating OxygenHilton M. Weiss Photosynthetic flora and microfauna utilize light from the sun to convert carbon dioxide and water into carbohydrates and oxygen. While these carbohydrates and their derivative hydrocarbons are generally considered to be fuels, it is the thermodynamically energetic oxygen molecule that traps, stores, and provides almost all of the energy that powers life on earth. Weiss, Hilton M. J. Chem. Educ.2008, 85, 1218.
Bioenergetics |
Metabolism |
Oxidation / Reduction |
Photosynthesis |
Thermodynamics
Undergraduates' Understanding of EntropyArnd H. Jungermann Szbilir and Bennett carried out an extensive investigation on undergraduates understanding of entropy. Though I agree in general with their statements that orderdisorder arguments form a misleading entropy concept, I would like to make some comments with regard to a certain part of their online supplement. Jungermann, Arnd H. J. Chem. Educ.2008, 85, 1192.
Thermodynamics
Using Graphs of Gibbs Energy versus Temperature in General Chemistry Discussions of Phase Changes and Colligative PropertiesRobert M. Hanson, Patrick Riley, Jeff Schwinefus, and Paul J. Fischer The use of qualitative graphs of Gibbs energy versus temperature is described in the context of chemical demonstrations involving phase changes and colligative properties at the general chemistry level. Hanson, Robert M.; Riley, Patrick; Schwinefus, Jeff; Fischer, Paul J. J. Chem. Educ.2008, 85, 1142.
Standard Enthalpies of FormationEd Vitz, John W. Moore A section of ChemPrime, the Chemical Educations Digital Library's free General Chemistry textbook.
A Lattice Energy SpreadsheetChristopher King A Lattice Energy Spreadsheet is a tool that easily calculates lattice energies. It also illustrates the relation between crystal structure, coordination number, and ionic radii. A Lattice Energy Spreadsheet contains five related worksheets: Lattice Energy, MX Structure Map, Kapustinsky Lattice Energy, Directions, and Discussion, each described below. In the Lattice Energy worksheet, the lattice energy of many binary compounds can be calculated in about a dozen mouse clicks. An element is selected, and the radius corresponding to the desired charge and coordination number is selected. The same is done for the counter ion, and the anticipated crystal structure of the compound is chosen (rock salt, wurtzite, etc.). The lattice energy is then calculated. This sheet uses enthalpies of formation of monatomic gaseous atoms from the elements, ΔH°form, to calculate lattice energies. The results are more accurate than the values obtained by simply summing enthalpies of fusion and vaporization. The results of the corresponding Born-Haber cycle are also graphed on this sheet.
