Chapter 3

# Marandsnoteschapter3thesecondlawofthermodynamics 123

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Unformatted text preview: ce between temperatures TA and TB is accompanied by a  change in entropy ΔSm.  ΔSm = TB ∫ TA T T B BC δqP dHm Pm ( T) =∫ =∫ dT   T T T T T A A where Cpm is the molar heat capacity at constant pressure of that  € substance. Obviously, the above equation is only valid if that substance  does not exhibit a phase change between the temperatures TA and TB.  The  above equation can be generalized to describe the change in entropy for  Marand’s Notes: Chapter 3 ‐ The Second Law of Thermodynamics  111  one mole of a pure substance, when it is heated at constant pressure  between 0 K and a temperature T. If we assume that at temperature T the  substance is in the vapor phase, then the change in entropy between 0 K  and T is given at the standard pressure by:  ΔS∅ m = S∅ m (T) − S∅ m Tfus (0) = ∫ 0 C S ( T) Pm T Tb CL ( T) Δ fusH∅ dT + + ∫ Pm dT Tfus T T fus T ∅ + Δ vapH Tb + ∫ Tb C V Pm ( T) T   dT where Tfus and Tb are respectively the melting (fusion) temperature of the  € substance in the solid state and the boiling (vaporization) temperature of  the substance in the liquid state at the standard pressure, PØ. In the above  equation, the quantities CPmS, CPmL and CPmV are the molar heat capacities at  constant pressure (P Ø) for the solid, liquid and vapor phases, respectively.   Calorimetric measurements allow us to measure specific heat capacities as  a function of temperature (for temperatures above a few kelvins) as well as  latent heats of phase transformation (standard enthalpy of fusion and  va...
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## This note was uploaded on 01/26/2014 for the course CHEM 3615 taught by Professor Aresker during the Spring '07 term at Virginia Tech.

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