物理化学学报 >> 2008, Vol. 24 >> Issue (01): 161-164.doi: 10.3866/PKU.WHXB20080129

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微量热法研究碱土金属离子与18-冠-6结合的热力学常数

刘鹏; 李曦; 潘牧   

  1. 武汉理工大学理学院应用化学系, 武汉 430070; 武汉理工大学材料复合新技术国家重点实验室, 武汉 430070
  • 收稿日期:2007-05-09 修回日期:2007-08-21 发布日期:2008-01-05
  • 通讯作者: 刘鹏 E-mail:chemliup@whut.edu.cn

Binding Thermodynamic Constants of Alkaline Earth Metal Ions with 18-Crown-6 Studied by Microcalorimetry

LIU Peng; LI Xi; PAN Mu   

  1. Department of Applied Chemistry, School of Sciences, Wuhan University of Technology, Wuhan 430070, P. R. China; State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070, P. R. China
  • Received:2007-05-09 Revised:2007-08-21 Published:2008-01-05
  • Contact: LIU Peng E-mail:chemliup@whut.edu.cn

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摘要： 通过微量热法研究了18-冠-6与碱土金属离子结合过程. 根据反应后的平衡关系, 求出反应平衡常数、焓、熵和吉布斯自由能变化. 金属离子由原来溶剂化的游离态变为与18-冠-6以静电力结合, 体系的能量降低, 放出了热量；同时由原来的自由运动变为被限制在冠醚孔穴内, 自由度减小, 熵值减少. 冠醚内的氧原子能够紧紧地围绕着半径为138 pm的Ba2+, 而离子半径较小的其它离子, 围绕得不够紧密, 与氧原子之间的作用力变小. 从Be2+、Mg2+、Ca2+、Sr2+到Ba2+, 与冠醚结合的放热增加, 平衡常数也逐渐增大.

关键词: 微量热, 滴定, 冠醚, 结合常数, 焓驱动

Abstract: The binding of alkaline earth metal ions with 18-crown-6 was studied by microcalorimetry. Equilibrium constant and changes of enthalpy, entropy, Gibbs free energy can be obtained from titration analysis. In the process of binding, the free metal ions bind to oxygen atom of 18-crown-6 by static force. The binding causes both energy and entropy in system to decrease, so reaction process was accompanied by release of heat and reduction of freedom. Having the similar size to ion radii (138 pm) of Ba2+, the cycle of 18-crown-6 can surround Ba2+ tightly. Metal ions with a smaller size have a weaker force to bind oxygen atom because of size effect. From Be2+, Mg2+, Ca2+, Sr2+ to Ba2+, more heat releases and equilibriumconstant increases in the process of the binding reaction.

Key words: Microcalorimetry, Titration, Crown ester, Binding constant, Enthalpy-driven