GENERAL CHEMISTRY CHEM 152
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This 15 page Class Notes was uploaded by Carmela Kilback on Wednesday September 9, 2015. The Class Notes belongs to CHEM 152 at University of Washington taught by Staff in Fall. Since its upload, it has received 28 views. For similar materials see /class/192597/chem-152-university-of-washington in Chemistry at University of Washington.
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Date Created: 09/09/15
Use ll Information AEqw AEanAT ManPAT V w P wrev ex initial d AS Sk1nQ bl M V AS nR1u quot Vinitial i T AS nCP 1 quot initial T AS nCv IHE 39w initial AG 2 AG RTlnQ and K Q at equilibn39um C c Dd aAbBcCdD szw A10 31 AH 1 AS 0 K1 R T2 T1 AHoncn ZCAHOf ZCAHOf Products reac an ix 0 2 o 0 AS rxn CS 2 CS produch reac an ts Aorcn ZCAGOf ZCAGOf Products reac an ts Lecture 9 Gibbs Free Energy Reading Zumdahl 107 109 0 Outline De ning the Gibbs Free Energy AG Calculating AG Pictorial Representation of AG Lecture 8 Summary AHOsys lt 0 AHOsys lt 0 De ning AG Recall the second law of thermodynamics AS AStotal AS ASsurr uniV system Also recall ASSUI39I39 Then AStotal AS AHsysT AHsysT system TAStotal TAS AHSys system De ning AG cont We then de ne AG TAStotal Then AG TASSys AHSys Or AG AH TAS AG The Gibbs Free Energy W P const AG and Spontaneous Processes Recall from the second law the conditions of spontaneity Three possibilities If ASumV gt O process is spontaneous If ASumV lt O process is spontaneous in opposite direction If ASumV O equi1ibrium In our derivation of AG we diVided by T therefore the direction of the inequality changes relative to entropy AG and Spontaneous Processes cont Three possibilities If ASuniV gt O process is spontaneous If ASumV lt O process is spontaneous in opposite direction If ASumV 0equi1ibrium In terms of AG If AG lt O process is spontaneous If AG gt O process is spontaneous in opposite direction If AG 0equi1ibrium Which of the following processes is spontaneous A A110 Sys TASS sys AH sys I ways I AH39Dsys TASQ s ys AG and Spontaneous Processes cont Note that AG is composite of both AH and AS AG AH TAS A reaction is spontaneous if AG lt 0 Such that If AH lt O and AS gt O spontaneous at all T If AH gt O and AS lt O not spontaneous at any T If AH lt O and AS lt O spontaneous at low T If AH gt O and AS gt O spontaneous at high T Example At What T is the following reaction spontaneous BI 21BI 2g Where AHO 3091 kJmol A80 932 JmolK 39 Ans AGO AHO TASO Example cont Try 298 Kjust to see AGO AHO TASO AGO 3091 kJmol 298K932 Jm01K AGO 3091 2778 kJmol 313 kJmol gt 0 Not spontaneous at 298 K Example cont At What T then AGO AHO TASO 0 T AHOASO T 3091 kJmol 932 JmolK T 33165 K Just like our previous calculation Calculating AGO In our previous example we needed to determine AHOIX11 and Asom to determine AGO I39Xl l Now AG is a state function therefore we can use known AGO to determine AGOIX11 using AGorxn ZAGopmd ZAGOreact Standard AG of Formation AGfO Like AH and SO AG is de ned as the change in free energy that accompanies the formation of 1 mole of that substance for its constituent elements with all reactants and products in their standard state Like AHfO AGfO O for an element in its standard state Example AGfO 02g O
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