Thermal Properties Based upon Heat Capacity and Decomposition Pressure of Tetramethylammonium Hydrogen Dichloride. Nature of the Hydrogen Bond in the Clsngbnd;Hsngbnd;Clmdash;Ion

摘要

The heat capacity of tetramethylammonium hydrogen dichloride was determined from 5deg; to 350deg;K by adiabatic calorimetry and the derived thermodynamic properties were calculated. No thermal anomalies were found. Molal values of heat capacity, entropy, and freehyphen;energy function at 298.15deg;K are 49.07, 60.63, and mdash;31.72 cal molemdash;1deg;Kmdash;1, respectively. The decomposition pressure of tetramethylammonium hydrogen dichloride, measured from 340deg; to 380deg;K with a Bourdon gauge as the null indicator, can be represented by the equation log10Pmm=mdash;28.4677ndash;1698.5Tmdash;1+15.502 log10Tmdash;0.012256T.Extrapolated values at 298.15deg; and 410.8deg;K are 1.8 and 760 mm Hg, respectively. Entropy increments for the decomposition reaction were calculated from the equilibrium data and compared with thirdhyphen;law entropy increment values derived from the thermal data. Excellent agreement was obtained. This provides strong support for the location of the equilibrium position of the hydrogen ion midway between the two chloride ions.