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 ΔHrxn≈ΔErxn (PΔV ≈ΔngasRT is small) ΔHrxnand ΔErxnare mostly due to bond breaking and formation Forming bonds releases energy (to surroundings) so exothermic ΔHrxnand ΔErxndepend slightlyon T, P Energetics of Phase Changes ΔHfus= ΔHrxnfor X(s) →X(l) ΔHvap= ΔHrxnfor X(l) →X(g) (measures average intermolecular force (total, per molecule)) •Generally 0 < ΔHfus< ΔHvapIntermolecular forces determine ΔHfus, ΔHvap, Tmand Tb Specific and Molar Heat Capacity c, and C (csand Cm) Calorimetry Constant V: Consant P: Coffee cup calorimetry Imagine two step process for exothermic rxn. 1.Reaction occurs. Products are higher T than reactants (ΔT). (q = 0 because insulated)2.
This is the end of the preview.
access the rest of the document.