Determination of Purity and Phase Behavior by Adiabatic Calorimetry

  • Edgar F. WestrumJr.

Abstract

Heating and cooling curves through the melting region of a substance allow calculation of the amount of impurity that is soluble in the liquid phase but insoluble in the crystalline phase as described by several investigators [e.g., 1, 2, 3] and highly developed by others [e.g., 4]. A more precise method of determining purity is the calorimetric procedure. In this technique, the temperature at which the crystalline and liquid phases are in equilibrium is determined as a function of the fraction of the sample liquefied. The depression of the freezing point and the enthalpy of fusion, and hence the cryoscopic constant, are determined in a single experiment. Precise results can be obtained because the sample can be held under adiabatic conditions as long as required for equilibration. The two procedures have been compared experimentally by Glasgow et al. [5]. The calculation of the purity of the sample from its equilibrium melting curve, which has been discussed by various investigators [6, 7, 8, 9, 10, 11, 12], involves straightforward application of ideal solution laws.

Keywords

Entropy Depression Enthalpy Benzene Fluoride 

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Copyright information

© Plenum Press 1968

Authors and Affiliations

  • Edgar F. WestrumJr.
    • 1
  1. 1.Department of ChemistryUniversity of MichiganAnn ArborUSA

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