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Barbi Della Polla
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This 2 page Class Notes was uploaded by Barbi Della Polla on Friday February 13, 2015. The Class Notes belongs to CHM 112 at University of Miami taught by Vanessa Falcao in Spring2015. Since its upload, it has received 17 views. For similar materials see Principles of Chemistry II in Chemistry at University of Miami.
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Date Created: 02/13/15
Class 0130 Heat Flow Entropy and the Second Law when ice is placed in water heat ows from the water into the ice According to the second law this happens because it results in more dispersal of heat The entropy of the universe increases Heat Transfer and Changes in Entropy of Surroundings The second law demands that the entropy of the universe increase for a spontaneous process 0 Yet processes like water vapor condensing are spontaneous even though the water vapor is more random than the liquid water o If a process is spontaneous yet the entropy change of the process is unfavorable there must have been a large increase in the entropy of the surroundings The entropy increase must become from heat released by the system the process must be exothermic Heat Exchange and A Ssurroundings Exothermic add heat to surroundings l increase entropy of sur Endothermic takes heat from the surroundings l decrease entropy of sur 0 The amount of entropy of the surroundings changes depends on its original temperature Temperature Dependence of A Ssurroundings When heat is added to surroundings that are cool it has more of an effect on the entropy than it would have if the surroundings were already hot Water freezes spontaneously below 0 C because the heat released on freezing increases the entropy of the surroundings enough to make A Spositive Quantifying Entropy Changes in Surroundings o The entropy change in the surroundings is proportional to the amount of heat gained or lost qsurroundings A o The entropy change in the surroundings is also inversely proportional to its temperature 0 At constant pressure and temperature the overall relationship is A Ssurroundings qsys AHsyS Gibbs Free Energy and Spontaneity Class 0130 AS univ sys surrl univ TA Suniv AH AH A n AS sys39 T sys39T I o The Gibbs free energy G is the maximum amount of work energy that can be released to the surroundings by a system for a constant temperature and pressure system A Gsys A H sys 39 39l Because AS umvdetermines if a process is spontaneous AG also determines spontaneity AS univis positive when spontaneous so AG is negative Gibbs Free Energy AG 0 A process will be spontaneous when AG is negative AH is negative and AS positive Exothermic and more random AH is negative and large and AS is negative but small low T AH is positive but small and AS is positive but large high T o A process will be nonspontaneous when AG is positive AH is positive and AS negative Never spontaneous at any temperature AH is negative and small and AS is negative and big AH is positive and AS is positive but small 0 When AG0 the reaction is at equilibrium TABLE 171 The Effect olf AH AS and T on Spentaneity AH As law Temperature High Temperature Example Spnntanleoua AG lt l Spontaneous AG d 0 2 NEDg gt 2 lN2g39 02g Nonspontaneous AG 3 390 Nonspontaneous AG i2gt D 302ng gt 2 03g Spontaneous AG lt 0 Nonspontaneous AG igt U Hl20l H2039S Nonspontanenus AG gt D Spontaneous AG lt D Hl20l 39gt Hl20g
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