Class Note for CHEM 112 at UMass(24)
Class Note for CHEM 112 at UMass(24)
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This 12 page Class Notes was uploaded by an elite notetaker on Friday February 6, 2015. The Class Notes belongs to a course at University of Massachusetts taught by a professor in Fall. Since its upload, it has received 17 views.
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Date Created: 02/06/15
Gibbs Free Energy G AGO AHO TASo Two methods of calculating AG aDetermine AH rxn and AS M and use Gibbs equation bUse tabulated values of free energies of formation AGf Free Energies of Formation Table 193 Standard Molar Free Energies of Formation ofSome Substances at 298 K ElementCompound A6kJmol ElementCnmpound 6kJmol lug u 02g 73944 02m a Cng 7503 N2g o H20g 72255 Cgiapnite 0 H200 72372 Cdiamond 2900 NH9 7154 09 71372 Fezuxs r7422 Note that AG for an element 0 Calculating AG rxn Combustion of acetylene C2Hzg 52 029 quotgt 2 0029 H20g Gibbs Free Energy G AGO AHO TASO Two methods of calculating AGO aDetermine AHorxn and ASODm and use Glbbs equation bUse tabulated values of free energies Of formation AGfO AG Xn Z AGf products 2 AGf reactants 4 Calcula rl ng AG rxn AG Xn Z AGf products 2 AGf reactants Combustion of carbon Cgraphite 029 gt 0029 Neighborhood Discussion Why is AG temperature dependant Can we predict what temperature would promote spontaneity mwmmn Dy mm s x and mm mm hwmhk my at man inmurnwws mum my mm mm mm 1 MawYe H leuwevamm nuummm AS new mm 4 gt11 Mtzmqu mun a PM A mm yummy rrAsltltn lemon 5 Muzmrimwu Mltltn 1wlta m Imam Temverawm Innev39 g Yunnanquot mm ng Mumquot AN ltnandAygtn am mmta Mum ltn prammmmn mmmm mm AH gta rummamm ltmptmmn m A gt n mm at quh r an lemp mmu Free Energy and Temperature 2 Fe203s 3 08 gt 4 Fes 3 0029 AHO 4679 kJ ASODm 5603 JK rxn At what T does AGorxn just change from being to being Estimate the temperature K at which the reaction below becomes spontaneous CaCO3s e CaO s 02 g AH 1790 kJ AS 1602 JK AG 1602 JK 13138 kJ Thermodynamics ond K6q FACT AGOrxn is the change in free energy when pure reactants convert to pure products FACT Productfavored systems have Therefore both AG rxn and Keq are related to reaction favorability 11 AG AG ond K6q AG is change in free energy at non standard conditions AG is related to AG AGAG RTnQ where Q reaction quotient When Q lt K or Q gt K reaction is spontaneous When Q K reaction is at When AG 0 reaction is at Therefore 12 AG AGquot and Keg Product Favored AG negative K gt 1 i Diffevence in ee energy ur pure restrain and puie products Spoiitaneuus rrrrrrrrrrrrrrrrrrrr reaztiun when U 5 K Increasing free energy 6 4 Reamnts Equilibrium Pmducis uniy mixtum unly nurse uf mama 13 Thermodynamics and Kea KEq is related to reaction favorability and so to AGDW The the value of K the more the value of AGDW AGOrxn RT InK where R 831 JKmol 14 Thermodynamics and Keq AGOxn RT InK Calculate Kfor the reaction N204 gt2 NO2 AG rxn 48 kJ 15 AG AG and Keq L as J gt 536 Productfavored JV as A a 2N02gtN204 2 A a L p AG rxn 48kJ Pawnquotisvrnductmmd Avignan State with both reactants and products present is more stable than complete conversion K more products than reactants lncreasing in energy a 15 AG AG and K8q w gt a Reactant favored A J 3 f A 39 N204quot39gt2 N02 g A t L 084 AG rxn48 kJ State with both reactants and products present is more stable than complete conversion 5 K more reactants than products lncreasmg m energy a Rustinquot cnnrdmate a 17 Thermodynamics and K8q Keq is related to reaction favorability When AG rxn reaction moves energetically downhill AG rxn is the change in free energy when reactants convert COMPLETELY to products 13 19 From Keq the energy balance at standard state AG0 can be determined With a value for A60 Keq can be calculated AG R nKeq Keq eXpAG RTJ AG M lgg at 298 K 250 24 x104 100 56 50 12 00 1 50 0084 100 0018 250 42 x 10395 Keq changes rapidly as a function of AG 20 The Propane Combustion Process C3H3 9 502 9 9 4H20 9 3002 9 PCSHB 1 atm P02 1 atm PHQO 1 atm P502 1 atm AG AG RTan The Propane Combustion Equilibrium C3H3 9 502 9 2 4H20 9 3002 9 o AG R739ane AG RTInKeq K50 eXpAG RT 21 When AGOrxn energetically downhill A mpow Greater than 0 Equal to 0 Less than 0 A B and C A amp C only reaction moves 22 What is the value of AG0 for the reaction below at 25 C Agaq C39aq 9 AgCIs Ksp v n 3910 A 56 kJmol 56 kJmol 56 X 103 56 X 103 56 X 10393 rnUOw 23
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