Solution Calorimetry Under Hydrothermal Conditions

Ion-pair formation in aqueous strontium chloride and strontium hydroxide solutions under hydrothermal conditions by AC conductivity measurements

“…50,57,58 Solvent polarization effects are reflected in the standard partial molar volumes of aqueous ions which rise to a maximum at B330 to 360 K as short-range hydration effects become less important, and then decrease towards large negative values at the critical point due to the electrostriction caused by long-range solvent polarization. 3,39,59 These conclusions are also supported by molecular dynamics (MD) simulations of SrCl 2 solutions under hydrothermal conditions by Svishchev et al 60 Pioneering MD studies by Balbuena et al 61 showed that the strongly bound first shell of both cations and anions persists well into the hightemperature, low-density range of supercritical water, and a welldefined second shell also persists into this region for the divalent cations. A more complete discussion of ionic hydration of Sr 2+ , Cl À and OH À under these conditions is given in the review by Seward and Driesner 62 and Driesner.…”

Standard Partial Molar Heat Capacities and Volumes of Aqueous N,N-Dimethylethanolamine and N,N-Dimethylethanolammonium Chloride from 283.15 to 393.15 K, and Ionization Constants to 598.15 K

“…The present study used more sensitive fixed-cell differential scanning nanocalorimeters, at a single concentration extrapolated to infinite dilution. Systematic uncertainties in both methods can typically be as large as 4 J·K –1 ·mol –1 . , The ionic strength dependence of apparent molar heat capacities and volumes of amines and amine salts has been measured as a function of temperature by Collins et al, Shvedov and Tremaine, Ford et al, and papers cited by Woolley . The systematic error in the application of eqs and to solutions of ionic strength ∼0.1 mol·kg –1 is typically less than ±0.5 cm –3 ·mol –1 and ±2 J·K –1 ·mol –1 above 298 K. The error in applying eq to neutral species is less than ±0.2 cm –3 ·mol –1 and ±1 J·K –1 ·mol –1 .…”

“…As a result, values for the heat capacity parameters Δ c , Δ d , and Δ e could be determined by fitting eq to the experimental data for C p ° from 283.15 to 393.15 K and using values of the g parameter obtained by regression to the high-temperature V ° data from Bulemela and Tremaine using eq . A similar approach has been used by Helgeson et al ,, in the HKF model , and Sedlbauer-O’Connell-Wood (SOCW) model . The form selected for the limiting high-temperature term in eqs , , and , which includes only the g fitting parameter, follows the approach adopted by Anderson et al, in which higher order terms in 1/ T were omitted in order to maintain a well behaved function for extrapolation.…”

“…This study made use of the methods developed by Woolley and his co-workers to measure V ° and C p ° from 283 ≤ T ≤ 598 K for DMEA­(aq) and its protonated form DMEAH + (aq) using commercial twin fixed-cell, power-compensation, differential-temperature scanning nanocalorimeters and vibrating tube densimeters. The advantages of the method are (i) unlike Picker type microcalorimeters, ,, these instruments measure relative volumetric heat capacities by scanning temperature, rather than measuring the properties of sequential solutions under isothermal conditions, and (ii) the temperature range of commercial instruments is much wider 283 ≤ T ≤ 598 K vs 283 ≤ T ≤ 328 K. As a result, measurements of C p ° extend well above the maximum in C p ° for ionic species, which typically lies in the range T ≈ 340 K, , so that extrapolations to hydrothermal conditions by fitting aqueous equation-of-state parameters are much more accurate. The heat capacity functions in this work were extrapolated to T > 570 K using a fit of the “density” model (eqs to ) to high temperature values for V °, in order to calculate thermodynamic functions for these species.…”

“…An alternative to direct measurements is to calculate equilibrium constants at high temperatures and pressures from the thermochemical properties at 298.15 K and temperature-dependent standard partial molar heat capacities and volumes of reaction, using extrapolated or fitted functions. − Standard partial molar volumes of DMEA and/or its protonated salt have been reported by several workers at near-ambient conditions. − Values for both the standard partial molar heat capacities and volumes of DMEA­(aq) and DMEAH + Cl – (aq) have been reported by Collins et al at temperatures from 283.15 to 328.15 K. There are no high temperature heat capacity measurements for DMEA­(aq) or DMEAH + Cl – (aq) in the current literature. The only such study to be carried out at elevated temperatures and pressures is that of Bulemela and Tremaine who measured the standard partial molar volumes of DMEA­(aq) and DMEAH + Cl – (aq) from 423.15 to 598.15 K at 15 MPa.…”