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Handout1001 - Lecture outline for Monday October 1...

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Lecture outline for Monday, October 1, 2007 (Chem 100, section 2) Topic: Energy of phases transitions and temperature changes Start with Review of Energy/Enthalpy Concepts Tabulated heats of reactions Exothermic: system heats surroundings Endothermic: surroundings heat system Δ H rxn Δ E rxn (P Δ V Δ n gas RT is small) Δ H rxn and Δ E rxn are mostly due to bond breaking and formation Forming bonds releases energy (to surroundings) so exothermic Δ H rxn and Δ E rxn depend slightly on T, P Energetics of Phase Changes Δ H fus = Δ H rxn for X(s) X(l) Δ H vap = Δ H rxn for X(l) X( g ) (measures average intermolecular force (total, per molecule)) Generally 0 < Δ H fus < Δ H vap Intermolecular forces determine Δ H fus , Δ H vap , T m and T b Specific and Molar Heat Capacity c, and C (c s and C m ) Calorimetry Constant V: Consant P: Coffee cup calorimetry Imagine two step process for exothermic rxn. 1. Reaction occurs. Products are higher T than reactants ( Δ T). ( q = 0 because insulated) 2.
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