Chemistry 20 Wednesday, October 18, 2006

Chemistry 20 Wednesday, October 18, 2006 - Wednesday,...

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Wednesday, October 18, 2006 Chemistry THE HEAT IS ON! How does reaction scale affect heat exchange? How does bond break/form affect heat exchange? TEXT: Sections 9.2 - 9.4 ENTHALPY CHANGES 1. Before: q + w = a way for system (reaction) to exchange E with surr. Now: Focus on heat changes in reactions 2. Enthalpy changes for process (∆ H) a. Heat exchanged at constant Pressure o can’t measure H of material o can’t measure ∆ H of process Endothermic Final (heat enters system) H Heat leaves surr. Initial (surr. Cool down) ∆ H + Initial Exothermic H (heat exits systems) Heat enters surr. Final (surr. heat up) ∆ H – 3. Heat exchange can result in: a. change in KE (temp.) b. change in volume c. change in PE (move charges) i. make/break bonds 4. ex. H 2 bond forms, E of system decreases (exothermic [top to bottom on picture of E changing]) put E in, bond breaks (endothermic[bottom to top on picture of E changing])
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Wednesday, October 18, 2006 5. In chemical reactions a. Some bonds broken
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This note was uploaded on 03/20/2008 for the course CH 101 taught by Professor Bigham during the Fall '08 term at N.C. State.

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Chemistry 20 Wednesday, October 18, 2006 - Wednesday,...

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