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chem notes 10-22 - -endothermic always positive-exothermic...

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October 22, 2007 Dr. Stevens Gen. Chem. 1 Chapter 6 Objectives: 1. know difference b/w heat and temp 2. ID exo and endothermic reactions 3. define and apply enthalpy to reactions 4. use equation for specific heat 5. calculate enthalpy from standard tables of reference data Energy: -thermal energy: energy associated with random motions of molecules (temperature) -chemical energy: energy stored in bonds (breaking/making bonds – reaction) -heat: transfer of thermal energy between 2 objects at different temperatures -temperature: measure of thermal energy -exothermic: releases energy -R P + q (products feel warmer) -endothermic: uses energy -R + q P (products feel cooler) Signs of energy change: -enthalpy(H): heat flow in a reaction at constant pressure -reaction change(H) = products(H) – reactants(H)
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Unformatted text preview: -endothermic: always positive-exothermic: always negative-reference point of change in enthalpy (delta H) delta H naught of formation (delta + H + “naught” + subscript f)-heat change that results when 1 mole of a compound is formed from its elements at 1atm pressure-O2 gas = 0-Fe solid = 0-Fe gas =\= 0-H2O liquid =\= 0-enthalpy of a reaction is enthalpy of product minus the enthalpy of reactants-aA + bB cC + dD-deltaHnaughtreaction = sum of all deltaHnaughtofformationproducts-…reactants-[cH(C) + dH(D)] – [aH(A) + bH(B)]-Ex: calc. enthalpy of reaction of 2C6H6(l) + 15O2(g) 12CO2(g) + 6 H2O-12(-393.5kJ/mol) + 6(-285.85kJ/mol) – 2(49.04kJ/mol) = -6535kJ/mol-exothermic...
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