Vapor pressures of 1.0-6.1 mol kg™1 aqueous sodium chloride were measured from 298 to 373K. The apparatus for measuring vapor pressures was modified to increase the convenience and the precision so that it could be operated by a single observer; the precision of measurement was ±0.002K or ±0.005 torr, whichever was larger. From these measurements, other vaporpressure and freezing-point measurements, and calorimetric enthalpies and heat capacities at 298K, 20 parameters of the modified Debye-Huckel-powerseries-in-the-molality equation were determined for aqueous sodium chloride. The equation was compared with measurements of the vapor pressure, the electromotive force of concentration cells, and thermal properties. The agreement was usually excellent.Previous static measurements of liquid-vapor equilibrium (33-35) indicated that the method is capable of even greater precision. Therefore, we reconstructed the cell and most of the auxiliary apparatus (9, 10). The changes which are of general interest were the replacement of the membrane null manometer by a liquid mercury manometer and the replacement of the air thermostat by an oil thermostat. The quantities to be measured were the equilibrium temperature and pressure, the total amount of each component, and the volume of the vapor phase.
Vapor pressures of aqueous 1.0-18.5m lithium chloride were measured from 25" to 100°C. From these measurements, other precise vapor-pressure and freezing-point measurements, and calorimetric enthalpy and heat capacity data, a 25-parameter quintic equation in the molality was developed for the nonDebye-Huckel part of the osmotic coefficient. With a similar equation for sodium chloride, the isotonic ratios of sodium chloride and lithium chloride were calculated and compared with literature values. The lithium chloride equation was compared with measurements of vapor pressure, freezing-point depression, and the electromotive force of concentration cells. The agreement is generally good.Recently, we reported static vapor-pressure measurements on aqueous sodium chloride ( 2 7 ) and synthetic seawater (2). The same apparatus with only minor changes was used to measure the vapor pressures of aqueous lithium chloride. The small size of the lithium ion relative to the sodium ion causes striking differences in the properties of the two chlorides in water. Lithium chloride is quite hygroscopic and has a molar solubility at 25°C more than three times greater than that of sodium chloride. The wide range of concentrations and water activities attainable with lithium chloride is one of the reasons it was chosen for study. ApparatusThe apparatus and procedure are the same as those described (27) except for one modification to improve the degassing procedure. Previous work (24) showed that an effective method for degassing nonelectrolyte solutions is to expand off the vapor from the cell while the solution is stirred at a temperature near the maximum temperature at which measurements are to be made. To adapt our apparatus for this degassing method, a mercury, porous glass frit valve was added to one arm of the solvent transfer U tube (Figure 1). During degassing, vapor is allowed to escape from the cell by lowering the mercury in the U tube to the level of the glass frit. The rate at which vapor escapes can be controlled roughly by adjusting the surface area of the frit which is exposed. The mercury, glass frit valve eliminates possible contamination of the cell with helium from the right side of the solvent transfer U tube, which must be pressurized at temperatures much above 25°C. MaterialsFisher reagent-grade lithium chloride was twice recrystallized from conductivity water and dried in a vacuum oven at 130°C. The solid was powdered and stored in the drying oven at 130°C until use. The purification and degassing of the water used in preparing solutions have been described ( 2 7 ) . ProcedureFinely powdered lithium chloride is added to the cell with a long-stemmed funnel through the ground glass joint G (Figure 1). This must be done quickly because the salt is extremely hygroscopic. The joint G is sealed with mercury, the cell is evacuated, and the system is pumped out for 24 hr at room temperature with a mercury diffusion pump. The salt is dissolved by distilling 6 ml of thoroughly degassed water from a reservoir with the cell...
A compact expression is derived for the change in any extensive thermodynamic state variable which accompanies an electrochemical reaction. The distinction between an electrochemical reaction and the complete thermodynamic change in state is clearly drawn. The cases in which every reactant is in a single, pure phase and that in which some reactants are dissolved in solution are discussed. Detailed calculations of all, AG, the cell potential, and the thermal efficiency of the lead/acid battery are presented as examples. Practical thermal ef~ciencies of II other systems are calculated and compared, where possible, with theoretical thermal efficiencies. Equations for the rate of heat flow from batteries are developed and applied to a typical duty cycle of a lead/acid battery for vehicular propulsion.
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