IMG_0001_NEW_0011 - their standard states Symbol(o"> process carried out under standard conditions(1 atm 1 M 298 K AHf:0 for element in its

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-t l Enthalpy and Hess's Law dj l' fll) For chemical reactions: M.eaction: Hproducts - Hreactants - Exothermic reactions, AFl. . O - Endothermic reactions, LH,> 0 Afi is an extensive property = LH is proportional to the amounts of substances in a system All changes sign when a process is reversed 4) 1/ is a State Function -+ Hess's Law LH is the same whether the reaction takes place in one step or in a series of steps (independent of pathw ay) Example: Use heat of combustion data to determine AH fbr the following reaction: 3C(.s) + 4Hr(g) -+ CrHr(g) e Standard Enthalpy of Formation (AHr') AHf : change in_Slltrglpy that occurs in the formation of 1 mole bf compound from its elements with all substances in
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Unformatted text preview: their standard states Symbol ((o" > process carried out under standard conditions (1 atm, 1 M, 298 K) AHf :0 for element in its standard state e,e oz(9), Na(s), Hg(D, ... 0. r L) . To Find AH" 1) Break reactant compounds into elemental forms 2) Construct products from elemental forms 3) M. .u.tion : Hfoprodu.r, -,F[o."u"1-1, . Example: Calculate the standard enthalpy of combustion of ethane - CrHu 10 2) 3) a ll I lr I nr i.i ;1rr. {f,l S,lt: t r;) i\il : I-+i!' :l r, 9i i., i *- ) i: rtrl , i [' P,v i"ti 1 :J i L I ,: 1, itr: -r- !( | i '' l;.; ;i 1''":11 ti I r r!'! c;{t.46lss"{l ({ttt-i I t_i + c ((, I ( li /.',...
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This note was uploaded on 12/27/2011 for the course CHEM 122 taught by Professor Williams during the Fall '10 term at Simon Fraser.

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