SATURATION THERMODYNAMIC FUNCTIONS FOR MERCURIC CHLORIDE
2989
The Saturation Thermodynamic Functions for Mercuric Chloride from 2 9 8 ° K to the Critical Point'
by Daniel Cubicciotti, H. Eding, and J. W. Johnson Stanford Research Institute, Menlo P a r k , California 94025
(Received A p r i l $9, 1966)
The saturation enthalpy increments above room temperature for HgC1, in its condensed phases were determined with a drop calorimeter to within 50" of the critical point. These were combined with previously determined enthalpies of vaporization to obtain values for the saturated vapor, and the data were extrapolated to the critical point. Saturation entropies for vapor and condensed phases were calculated from the enthalpies. The internal energy departures of the gas from ideal values were evaluated and compared with similar data for molecular fluids.
Introduction The present report is a part of our study of the thermodynamic properties of inorganic liquids a t elevated temperatures. Recent investigations of bismuth chloare being followed by studies on mercuric chloride. The volume change on vaporization5 and the vapor pressure6 of HgCl, up to its critical point were determined previously in this laboratory, and the enthalpy and entropy of vaporization have been obtained from those results. In the present paper, we have determined the enthalpy increments (above the solid at 298°K) for the condensed phases under saturation conditions, and from them and the enthalpies of vaporization we have ohtained values for the saturated vapor. The entropies and free energy functions for both the condensed and gas phases were calculated from the enthalpy increments and their temperature derivatives.
the vapor pressure of the HgCl?. As a result, a substantial fraction of the heat evolved came from the glass, and so the accuracy of those determinations was limited. To obtain more accurate data in the lower temperature range, where the vapor pressure was low enough, sealed platinum containers were used. The important details of the samples are listed in Table I.
Table I : Details of Samples Used W t of Sample no.
Container material
A B C D
Quartz glass Quartz glass Quartz glass Platinum
HgClz, g
24 7 5 13
0608 0609 3083 4660
Wt of container, g
6 8617 6 4409 6 077!) 7 7860
Internal vol of ampoule, cc
Symbol used In F~gures 1 and 2
6 9181 2 0801 2 2132
0 8 @ X
Measured Heat Increments The same method was used for this work as reported in our BiCls study:4 samples of HgCI, sealed in evacuated quartz glass ampoules were heated to various temperatures, some within 50" of the critical temperature, and dropped into a modified Parr calorimeter at room temperature. From the heat transferred to the calorimeter, the enthalpy of HgCI, in the condensed phases, under saturation conditions, was calculated. The samples heated to the higher temperatures required heavy-walled glass ampoules to withstand
(1) Thiz work was made possible by financial support from the Research Division of the U. s. Atomic Energy commission under Contract No. AT(04-3)-106. (2) 3. W. Johnson and D. Cubicciotti, J. Phvs. Chem., 68, 2235 (1964). (3) J. W. Johnson, W. J . Silva, and D. Cubicciotti, ibid., 69, 3916 (1965). (4) D. Cubicciotti, H. Eding, F. J . Keneshea, a n d J. W. Johnson, ibid., 70, 2389 (1966). ( 5 ) J. W. Johnson, W. J . Silva, and D. Cubicciotti, ibid., 70, 1169 (1966). (6) J. W. Johnson, W.J. Silva, and D. Cubicciotti, ibid., 70, 2985 (1966).
Volume '70, Number 9 September 1966
2990
A small part of the heat liberated by the sample was due to condensation of HgC1, vapor. The amount of that heat for each drop was calculated from the known liquid and vapor densities and the volumes of the ampoules. For the calculation, the enthalpy of vaporization at the sample temperature was used instead of the more complicated calculation of integration over the range of temperatures for which condensation occurred. Since the total correction was small, the difference in methods of calculation was negligible. For determinations made belo\v 700"I
