ICC CHEM 132 - Thermodynamics and Equilibrium

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Chemistry 132 NTThermodynamics and EquilibriumReviewFree Energy ConceptFree Energy and SpontaneityStandard Free-Energy ChangeA Problem To ConsiderSlide 8Slide 9Slide 10Standard Free Energies of FormationSlide 12Slide 13Slide 14DGo as a Criteria for SpontaneitySlide 16Slide 17Maximum WorkSlide 19Free Energy Change During ReactionFigure 18.9 Free-energy change during a spontaneous reaction.Slide 22Figure 18.10 Free-energy change during a nonspontaneous reaction.Relating DGo to the Equilibrium ConstantSlide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Spontaneity and Temperature ChangeCalculation of DGo at Various TemperaturesSlide 34Slide 35Slide 36Slide 37Slide 38Slide 39Slide 40Slide 41Slide 42Slide 43Slide 44Slide 45Operational SkillsKey EquationsSlide 48HomeworkPowerPoint Presentation11111Chemistry 132 NTI wish I would have a real tragic love affair and get so bummed out that I’d just quit my job and become a bum for a few years, because I was thinking about doing that anyway.Jack Handey22222Thermodynamics and EquilibriumChapter 18Module 2Sections 18.4, 18.5, 18.6 and 18.7Photomicrograph of urea crystals under polarized light.33333ReviewCalculating the entropy change for a phase transitionPredicting the sign of the entropy change of a reactionCalculating So for a reaction44444Free Energy ConceptThe American physicist J. Willard Gibbs introduced the concept of free energy (sometimes called the Gibbs free energy), G, which is a thermodynamic quantity defined by the equation G=H-TS.This quantity gives a direct criterion for spontaneity of reaction.55555Free Energy and SpontaneityChanges in H an S during a reaction result in a change in free energy, G , given by the equationThus, if you can show that G is negative at a given temperature and pressure, you can predict that the reaction will be spontaneous.STHG 66666Standard Free-Energy ChangeThe standard free energy change, Go, is the free energy change that occurs when reactants and products are in their standard states.The next example illustrates the calculation of the standard free energy change, Go, from Ho and So.oooSTHG 77777A Problem To ConsiderWhat is the standard free energy change, Go , for the following reaction at 25 oC? Use values of Hfo and So, from Tables 6.2 and 18.1.Place below each formula the values of Hfo and So multiplied by stoichiometric coefficients.)g(NH2)g(H3)g(N322So: 3 x 130.6191.5 2 x 193 J/KHfo:00 2 x (-45.9) kJ88888A Problem To ConsiderWhat is the standard free energy change, Go , for the following reaction at 25 oC? Use values of Hfo and So, from Tables 6.2 and 18.1.You can calculate Ho and So using their respective summation laws.)g(NH2)g(H3)g(N322)reactants(Hm)products(HnHofofokJ 8.91kJ ]0)9.45(2[ 99999A Problem To ConsiderWhat is the standard free energy change, Go , for the following reaction at 25 oC? Use values of Hfo and So, from Tables 6.2 and 18.1.You can calculate Ho and So using their respective summation laws.)g(NH2)g(H3)g(N322)reactants(Sm)products(SnSoooJ/K -197J/K )]6.13035.191(1932[ 1010101010A Problem To ConsiderWhat is the standard free energy change, Go , for the following reaction at 25 oC? Use values of Hfo and So, from Tables 6.2 and 18.1.Now substitute into our equation for Go. Note that So is converted to kJ/K.)g(NH2)g(H3)g(N322kJ/K) 0.197K)( (298kJ 91.8 oooSTHG kJ 33.1(see Exercise 18.6 and Problem 18.37)1111111111Standard Free Energies of FormationThe standard free energy of formation, Gfo, of a substance is the free energy change that occurs when 1 mol of a substance is formed from its elements in their most stable states at 1 atm pressure and 25 oC.By tabulating Gfo for substances, as in Table 18.2, you can calculate the Go for a reaction by using a summation law.)reactants(Gm)products(GnGofofo1212121212A Problem To ConsiderCalculate Go for the combustion of 1 mol of ethanol, C2H5OH, at 25 oC. Use the standard free energies of formation given in Table 18.2.)g(OH3)g(CO2)g(O3)l(OHHC22252Gfo:-174.8 0 2(-394.4) 3(-228.6)kJPlace below each formula the values of Gfo multiplied by stoichiometric coefficients.1313131313A Problem To ConsiderCalculate Go for the combustion of 1 mol of ethanol, C2H5OH, at 25 oC. Use the standard free energies of formation given in Table 18.2.)g(OH3)g(CO2)g(O3)l(OHHC22252You can calculate Go using the summation law.)reactants(Gm)products(GnGofofokJ )]8.174()6.228(3)4.394(2[GoGfo:-174.8 0 2(-394.4) 3(-228.6)kJ1414141414A Problem To ConsiderCalculate Go for the combustion of 1 mol of ethanol, C2H5OH, at 25 oC. Use the standard free energies of formation given in Table 18.2.)g(OH3)g(CO2)g(O3)l(OHHC22252You can calculate Go using the summation law.)reactants(Gm)products(GnGofofokJ 8.1299GoGfo:-174.8 0 2(-394.4) 3(-228.6)kJ(see Exercise 18.7 and Problem 18.41)1515151515Go as a Criteria for SpontaneityThe following rules are useful in judging the spontaneity of a reaction.1. When Go is a large negative number (more negative than about –10 kJ), the reaction is spontaneous as written, and the reactants transform almost entirely to products when equilibrium is reached.1616161616Go as a Criteria for SpontaneityThe following rules are useful in judging the spontaneity of a reaction.2. When Go is a large positive number (more positive than about +10 kJ), the reaction is nonspontaneous as written, and reactants do not give significant amounts of product at equilibrium.1717171717Go as a Criteria for SpontaneityThe following rules are useful in judging the spontaneity of a reaction.3. When Go is a small negative or positive value (less than about 10 kJ), the reaction gives an equilibrium mixture with significant amounts of both reactants and products.(see Exercise 18.8 and Problem 18.45)1818181818Maximum WorkOften reactions are not carried out in a way that does useful work.As a spontaneous precipitation reaction occurs, the free energy of the system decreases and entropy is produced, but no useful work is obtained.In principle, if a reaction is carried out to obtain the maximum useful work, no entropy is produced.1919191919Maximum WorkOften reactions are


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ICC CHEM 132 - Thermodynamics and Equilibrium

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