L24S07_Thermchem, Enthalpy 03-14-07

L24S07_Thermchem, Enthalpy 03-14-07 - Chem 1A L24:...

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Unformatted text preview: Chem 1A L24: "Thermochemistry, Enthalpy" First Law of Thermodynamics w:work + System (you can't win) E = q + w Work for Gases Pext = F/A Previously Conservation of E E is a state function Euniv = Esys + Esurr = 0 L22-4 w = - F h = - Pext V hh3 E = 2 nRT Expansion Compression 3 - + q:heat V > O w<O A.Pines, M.Kubinec,UCB V < O w>O L29-6 Surroundings A.Pines, M.Kubinec,UCB Isothermal Expansion/Compression Pext = F/A Adiabatic Expansion/Compression Pext = F/A Const T : E = H = 0 hh- q = 0 : E = w hhExpansion w<O E < O A.Pines, M.Kubinec,UCB q + ww 0 =- = Expansion wq+ Compression w+ qL22-12 Compression w>O E > O A.Pines, M.Kubinec,UCB 2004 M. Kubinec, A. Pines L24-1 L22-14 Constant Volume / Pressure Pext E = q + w Volume Energy E w=0 E = qv E T Pressure Enthalpy H = E + PV H = E + PV P H = q p H T L24-2 Open to Atmosphere 2004 M. Kubinec, A. Pines ChemQuiz 23.1 An ideal gas expands isothermally against a vacuum.What is q ? vacuum.What Pext = 0 Expansion V > O wO h+ 1) < 0 2004 M. Kubinec, A. Pines 2) = 0 3) > 0 L24-3 2004 M. Kubinec, A. Pines 1 Chem 1A L24: "Thermochemistry, Enthalpy" ChemQuiz 23.2 An ideal gas is isothermally compressed. What is q ? h- 1) < 0 2004 M. Kubinec, A. Pines 2) = 0 3) > 0 L24-5 Isothermal Expansion/Compression Pext = F/A Const T : E = H = 0 Expansion V > O wO h+ q + ww 0 =- = Expansion wq+ L24-7 2004 M. Kubinec, A. Pines Isothermal Expansion/Compression Pext = F/A Const T : E = H = 0 h- q + ww 0 =- = Expansion wq+ Compression w+ qL24-8 2004 M. Kubinec, A. Pines 2004 M. Kubinec, A. Pines 2 Chem 1A L24: "Thermochemistry, Enthalpy" Adiabatic Expansion/Compression Pext = F/A q = 0 : E = w Expansion V > O wO h+ Expansion w<O E < O L24-9 2004 M. Kubinec, A. Pines Adiabatic Expansion/Compression Pext = F/A q = 0 : E = w hExpansion w<O E < O 2004 M. Kubinec, A. Pines Compression w>O E > O L24-10 ChemQuiz 23.3 A gas expands adiabatically against a constant pressure. pressure. What happens to the temperature of the gas ? 1) Increases 2004 M. Kubinec, A. Pines 2) Same 3) Decreases L24-11 2004 M. Kubinec, A. Pines 3 Chem 1A L24: "Thermochemistry, Enthalpy" ChemQuiz 23.4 A stretched rubber band is suddenly released. What happens released. to the temperature of the rubber band ? 1) Increases 2004 M. Kubinec, A. Pines 2) Same 3) Decreases L24-13 Thermochemistry Summary E q+ qSurroundings A.Pines,M.Kubinec,UCB aA+bB q = H cC+dD Standard Enthalpy of Formation Enthalpy Compounds Hill Endothermic: q > 0 H > 0 Heat is absorbed Heat is released System Exothermic: q < 0 H < 0 Standard States: H 1M, 1atm, 25C L19-14 Elements in Standard States Hf 0 Compounds A.Pines,M.Kubinec,UCB L19-7 Standard Enthalpy Change Reactants Hf(R) Products Hf(P) Hf H2(g) O2(g) C(s) Al(s) Fe(s) N2(g) Standard Enthalpies of Formation (kJ mol-1) 0 +218 +249 +473 C(g) CO2(g) H20(l) H20(g) +717 -394 -286 -242 CH3CH2OH (l) -278 -1274 -824 -1676 L24-15 L19-9 Elements in Standard States H = Hf(P) Hf(R) A.Pines,M.Kubinec,UCB 0 H(g) O(g) N(g) C6H12O6 (s) Fe2O3 (s) Al2O3 (s) 2004 M. Kubinec, A. Pines L19-8 A.Pines,M.Kubinec,UCB Thermochemistry aA+bB q = H cC+dD System Endothermic: q > 0 H > 0 E Heat is absorbed System q+ Surroundings 2004 M. Kubinec, A. Pines L24-16 2004 M. Kubinec, A. Pines 4 Chem 1A L24: "Thermochemistry, Enthalpy" Thermochemistry aA+bB q = H cC+dD System Endothermic: q > 0 H > 0 E Heat is absorbed Heat is released System Exothermic: q < 0 H < 0 qSurroundings Standard States: H 1M, 1atm, 25C L24-17 2004 M. Kubinec, A. Pines ChemQuiz 24.1 H for the reaction H2O (g) H2O (l) is +44 kJ mol-1. Which is most hazardous at 100C ? 1) Water 2) Steam 3) Water/Steam 2004 M. Kubinec, A. Pines L24-18 ChemQuiz 24.2 HH H H H C C C OH HH H Propanol HOH H C C C H H HH H Isopropanol The isomerization of propanol is endothermic. Which burns cooler? endothermic. cooler? 1) Propanol 2) Isopropanol 3) Same 2004 M. Kubinec, A. Pines L24-20 2004 M. Kubinec, A. Pines 5 Chem 1A L24: "Thermochemistry, Enthalpy" Standard Enthalpy of Enthalpy Formation Compounds Hill Elements in Standard States H 0 Compounds 2004 M. Kubinec, A. Pines L24-22 Standard Enthalpy Change Reactants Hf(R) (R) Products Hf(P) (P) H Elements in Standard States H = Hf(P) Hf(R) (P) (R) 2004 M. Kubinec, A. Pines 0 L24-23 Standard Enthalpies of Formation (kJ mol-1) H2(g) O2(g) C(s) Al(s) Fe(s) N2(g) 0 +218 +249 +473 C(g) CO2(g) H20(l) H20(g) +717 -394 -286 -242 CH3CH2OH (l) -278 -1274 -824 -1676 L24-24 H(g) O(g) N(g) C6H12O6 (s) Fe2O3 (s) Al2O3 (s) 2004 M. Kubinec, A. Pines 2004 M. Kubinec, A. Pines 6 Chem 1A L24: "Thermochemistry, Enthalpy" ChemQuiz 24.3 What is H (kJ mol-1) for the oxidation of Fe ? Fe (s) + O2 (g) Fe2O3 (s) Fe LO2 1) -575 2004 M. Kubinec, A. Pines 2) -824 3) -1073 L24-25 ChemQuiz 24.4 Which of the following will react with Fe2O3 to produce molten Fe? Fe? 1) C (s) 2) Fe (s) 3) Al (s) 2004 M. Kubinec, A. Pines L24-27 Lecture Complete 2004 M. Kubinec, A. Pines L24-29 2004 M. Kubinec, A. Pines 7 ...
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