Determination of the specific heat capacities of aqueous sodium chloride solutions at high pressure with the temperature jump technique

Abstract

In this work specific heat capacities have been measured by the temperature jump technique. Electrical energy stored in a high voltage capacitor is discharged through the electrically conducting solution; this causes a rise in temperature which is measured indirectly by the optical absorbance change of a buffered indicator system. Cy data are reported for aqueous sodium chloride solutions in the concentration range from 0.1 to 2.0 mol kg"1 at 293 K at 1 and 2 kbars. All cy values decrease with increasing pressure. At 1 bar and 1 kbar cy decreases monotonously with increasing salt concentration whereas at 2 kbars a maximum appears. Using data for compressibility and cubic expansion coefficients cv was converted to cp; its dependence on pressure and salt concentration, respectively, is similar to the behavior of cy. The data obtained are discussed with respect to structural effects. From the volume dependence of cv and the pressure dependence of cp, the temperature dependence of (ep/dT)v and of (aV/aT)p, respectively, is calculated; with increasing salt concentration the temperature dependence of both decreases.

Volumetric properties of aqueous solutions of lithium chloride at temperatures from 278.15 K to 338.15 K and molalities (0.1, 0.5, and 1.0)mol · kg−1

“…At constant temperature T = 298.15 K with increasing lithium chloride concentration (figures 13, 14) the effect of pressure on C p decreases (the same dependence is observed at T = 293.15 K and at 1 and 2 kbars for sodium chloride solutions (64) ). The unusual high heat capacity of water is often attributed to a highly ordered structure of water.…”

Volumetric properties of aqueous solutions of disodium tartrate and dipotassiuml-tartrate at temperatures from 278.15 K to 343.15 K and molalities (0.1, 0.5, and 1.0) mol·kg−1

“…the heat capacity of disodium tartrate and dipotassium L-tartrate solutions decreases with increasing pressure, which is typical for pure water (8,20) and other electrolytes. (3,18,19,(21)(22)(23)(24) Differences between the tartrate solutions and pure water,…”

Thermal Properties of the H2O–CO2–Na2CO3/CH3OH/NH3 Systems at Low Temperatures and Pressures up to 50 MPa

“…Changes in CO 2 surroundings along the studied pressure–temperature paths must be considered while interpreting the results of the present study, where the molecule is first dissolved in the aqueous solutions, then “enclathrated” upon cooling, and finally released by heating. The addition of salts, methanol, or ammonia to water-rich phases decreased both specific heat capacity and enthalpy. − These values for these compounds in the solid state, forming salt hydrates, are usually within the ranges of 1–2 J g –1 K –1 and 100–300 J g –1 . , …”