Abstract The analysis of the melting point of molecular crystals requires a spontaneous perspective on the melting process, considering both the enthalpy change of melting (ΔHm) and the entropy change of melting (ΔSm). ΔHm is directly related to intermolecular forces, where a larger ΔHm results in a higher melting point. Intermolecular forces primarily consist of hydrogen bonds and van der Waals forces. Apart from strongly polar molecules, van der Waals forces, primarily composed of dispersion forces, are influenced by factors such as relative molecular mass, molecular deformability, and intermolecular distance. Simultaneously, molecular deformability increases the ΔSm during the melting of molecular crystals. A larger ΔSm leads to a lower melting point of molecular crystals. Hence, analyzing the melting point of molecular crystals necessitates attention to molecular deformability. Teachers should actively engage in targeted learning to enhance their knowledge structure and deepen their understanding of the chemistry discipline. This approach enables the identification of the primary influencing factors among the numerous elements affecting the melting point.
WENG Xue-Xiang, ZHOU Qi-Xin, WU Chao-Hui. Subject Understanding: Analyzing Melting Points of Molecular Crystals Should Consider Both Enthalpy Change and Entropy Change of Melting[J]. Chinese Journal of Chemical Education, 2024, 45(23): 99-103.
