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Unformatted text preview: 10/13/09 Chapter 10 For an isothermal process, reversible process, S=q rev /T Phase Transitions Fusion (melting): solid liquid liquid solid Vaporization liquid gas gas liquid q p =H S fusion =H fusion /T f S vap =H vap /T v We can determine the differences in the entropies of states in the same manner as we determined differences in E and H Entropies are unique in that the absolute values of entropies can be determined 1 st we must understand how entropies change with T For an isothermal reversible process: Ssystem=qrev/T qrev=TS qp=H=nCpT qv=E=nCpT Calculate S for a temperature change (T1 T2) S=nCpT/T S=nCvT/t S=nCpln(T1/T2) S=nCvln(T1/T2) Unlike H and E, we know the value of the absolute entropies of all substances at one temperature 0 K 3 rd Law of Thermodynamics: the entropy of an ideal crystal at 0 K is zero The degree of vibration is a function of the energy available to the crystal The degree of vibration is a function of the energy available to the crystal...
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