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  Home > JCE Print > Journal of Chemical Education > Issues > 2006  > September  >
Research: Science and Education
Are Crystallization and Melting the Reverse Transformation of Each Other?
Hermínio P. Diogo
Centro de Química Estrutual, Complexo I, IST, 1049-001 Lisboa, Portugal

Joaquim J. Moura Ramos
Centro de Química-Física Molecular, Complexo I, IST, 1049-001 Lisboa, Portugal

Cover
September 2006
Vol. 83 No. 9
p. 1389
Abstract
This article examines the pedagogical issue of teaching phase changes from a non-equilibrium perspective, and specifically demonstrates that crystallization is often not the simple reverse of melting. Differential scanning calorimetry is used to analyze four compounds that show different properties as the liquid and solid phases interconvert. Crystallization is shown to be a two-step process (nucleation and crystal growth). These steps are shown to exhibit both thermodynamic and kinetic control of the overall crystallization process, making it far more complex than the single-step, thermodynamically controlled melting process.
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A more complete presentation of classical nucleation and crystal growth theories is available.
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Citation
Diogo, Hermínio P.; Moura Ramos, Joaquim J. J. Chem. Educ. 2006 83 1389.
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Keywords
Calorimetry / Thermochemistry; Crystals / Crystallography; Liquids; Phases / Phase Transitions / Diagrams; Physical Chemistry; Solids; Thermal Analysis; Thermodynamics; Thermodynamics; Upper-Division Undergraduate
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History
Created:
Last Updated:
8/7/2006
8/18/2006
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