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Uses of Cp Equations H s (298 K) = H v (298 K) + H fus (298 K) The fusion, vaporization and sublimation enthalpies of biphenyl are given below. Evaluate these thermodynamic properties at T = 298.15 K and check to see that they are internally consistent. H s (311 K) = 82.5 kJ mol -1 H v (363 K) = 59.6 kJ mol -1 H fus (341.5 K) = 18.66 kJ mol -1 H s 59.6 + 18.7 = 78.3 kJ mol -1

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Biphenyl H s (311 K) = 82.5 kJ mol -1 H s (298 K) = H s (311 K)+(0.71+0.15 Cp(c) calc )[311-298] Cp(c) calc = 10*17.5+2*8.5 Cp(c) calc = 192 J mol -1 K -1 H s (298 K) = 82.5 +(0.38 0.1) H s (298 K) = (82.9 0.1) kJ mol -1

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Biphenyl H s (298 K) = (82.9 0.1) kJ mol -1 H v (363 K) = 59.6 kJ mol -1 H v (298 K) = H v (363 K) +(10.58+0.26 Cp(l) calc )[363-298] Cp(l) calc = 10*21.8+2*15.3 Cp(l) calc = 248.6 J mol -1 K -1 H v (298 K) = 59.6 + (4.88 0.98) H v (298 K) = (64.5 1.0) kJ mol -1

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Biphenyl H s (298 K) = 82.9 kJ mol -1 H v (298 K) = 64.5 1.0 kJ mol -1 H fus (341.5 K) = 18.66 kJ mol -1 H fus (298 K) = H fus (341.5 K) +)+[0.15Cp(c) - 0.26Cp(l)- 9.83][T fus -298] H fus (298 K) = 18.66 -(1.98 0.6) H fus (298 K) = (16.7 0.6) kJ mol -1 H s (298 K) = (64.5 1.0) + (16.7 0.6) H s (298 K) = (81.2 1.2) kJ mol -1

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NIST Webbook A valuable source of thermochemical information http://webbook.nist.gov/chemistry/

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The vaporization enthalpy of anthracene has been measured over the temperature range T = 496-555 K; H v = 59200 200 J mol -1. The fusion enthalpy was measured as H fus (489K) = 29370 100 J mol -1. What is the sublimation enthalpy of anthracene at T = 298.15 K?

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Estimation of Vaporization Enthalpies 1. Group additivity by Guthrie and Taylor Can J. Chem.1983, 61, 602-607. 2. Group additivity by Ducros, M.; Gruson, J. F.; Sannier, H. Thermochimica Acta 1980, 36, 39-65; Ducros, M., Gruson, J.F., and Sannier, H., Thermochimica Acta, 1981, 44, 131-140. DuCros, M. Sanier, H. Thermochim. Acta 1982, 54, 153- 157; Ducros, M.; Sannier, H. Thermochimica Acta 1984, 75, 329-340. 3. “Group Additivity” of Chickos, J. S.;Acree, Jr. W. E.; Liebman, J. F. “Computational Thermochemistry”, Irikura, K. K.; Frurip, D. J. Edit. ACS 1996.

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H v (298) Estimation of Hydrocarbons H v (298)/kJmol -1 =4.69(n C -n Q )+1.3n Q + 3.0 n Q refers to a quaternary sp3 carbon atom H v (298)Estimation of Monosubstituted Hydrocarbon Derivatives H v (298)/kJmol -1 =4.69(n C -n Q )+1.3n Q +3.0+n M M +b +C

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H v (298) Estimation of Hydrocarbons Estimate H v (298) for cycloheptatriene H v (298)=4.69(n C -n Q )+1.3n Q + 3.0 H v (298) = 39.4 kJmol -1 (literature) Estimate H v (298) for 2-nitrotoluene H v (298) = 59.1 kJmol -1 (literature)

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H v (298) Estimation of Polysubstituted Hydrocarbon Derivatives

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Estimate H v (298) of 1,2-dichlorobenzene C 6 H 4 Cl 2 1,2-dichlorobenzene[95-50-1] 51.2(256)[99/20] (363-454)44.5(376)EB[98/8] (256-287)50.8(271)[96/19] (413-453)50.9(298)GC[94/22] (258-313)51.2GC[94/23] (373-453)44.0(388)A[87/5] (360-450)49.9(298)[84/9][91/2] (301-343)50.0(322)GS[82/1]

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Estimate the vaporization enthalpy of perfluoro-2- methylbutane. Estimate the vaporization enthalpy of nonafluorocyclopentane Estimate the vaporization enthalpy of dibutyl disulfide

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Estimate the vaporization enthalpy of 2-propoxyethanol Estimate the vaporization enthalpy of 2-isopropoxyethanol Estimate the vaporization enthalpy of 2,2-dimethoxypropane

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Chapter 17: Thermochemistry

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