Heat Capacities Of Aqueous Solutions Research Articles

Heat capacities of aqueous solutions of nickelous chloride and nickel chloride-sodium chloride (NiCl2.2NaCl) from 0.12 to 3.0 mol kg-1 and 321 to 572 K at a pressure of 17.7 MPa

Heat capacities of aqueous solutions of nickelous chloride and nickel chloride-sodium chloride (NiCl2.2NaCl) from 0.12 to 3.0 mol kg-1 and 321 to 572 K at a pressure of 17.7 MPa

Determination of the Specific Heat Capacities of Aqueous Solutions of Pentose

Abstract A laboratory-constructed isoperibol twin calorimeter of dry shield type (J. Chem. Thermodyn., 13, 89 (1981)) was used for measurements of the specific heat capacities of aqueous solutions of d-xylose, d-ribose, d-, and l-arabinose at ca. 30 °C. The partial molar heat capacity at infinite dilution, Cp.2∞ was determined. Values of Cp.2∞ obtained are: d-xylose 281±2, d-ribose 271±2, d-arabinose 278±3, and l-arabinose 270±4 J K−1 mol−1. Measurements of the heat capacity of these pentoses in the solid state, Cp.2* were carried out and the parameter ΔCp.2∞≡Cp.2∞–Cp.2* was evaluated. Values of ΔCp.2∞ are smaller than the corresponding values for hexose obtained previously. Similarly as had been the case for hexose, the additivity parameters of the group contribution on Cp.2∞ of solute estimated from the data on other nonelectrolytes were not acceptable for pentose. From this point the interactions working between solute of saccharide and the solvent water are considered to have characters largely different from those of other nonelectrolyte.

Experimental Study of Dynalnic Specific Heat Capacity of Protein Aqueous Solutions

We performed the measurements of the dynamic heat capacity of aqueous solutions of lysozyme and α-chymotrypsin near heat denaturation by using an ac calorimeter. The obtained values of the ac enthalpy and the ac entropy at the heat denaturation process were much smaller than those measured by usual dc calorimeters. This fact tells us that the main part of the dynamic denaturation process takes place at a frequency lower than our measuring frequency of 0.6 Hz, in consistent with the results given by T-jump experiments. Furthermore, it was clarified by a circular dichroism measurement that the disulfide bridges play an important role in holding the three-dimensional structure of the proteins.

Aqueous solutions of azoniaspiroalkane halides. VI. Apparent molal volumes and apparent molal heat capacities of chlorides and iodides

Densities and heat capacities of aqueous solutions of azoniaspiroalkane halides, (CH2)nN+ (CH2)nX− (where X=Cl, I andn=5,6), have been measured at 25°C using a flow densimeter and a flow microcalorimeter. The limiting apparent molal volumes (ov∘) and apparent molal heat capacities (ocp∘) obtained from these data are compared with those of the azoniaspiroalkane bromides and the corresponding tetraalkylammonium halides. The concentration dependence of ov and ocp are examined for clues on the influence of solute hydration, structure, and conformational flexibility on the excess functions of quaternary ammonium halides.

A contribution to the debate about hydrophobic effects

Based on available measurements of the concentration dependence of the volume and the heat capacity of aqueous solutions of low molecular weight compounds it is suggested that non-polar molecules or non-polar groups in aqueous solution fluctuate between solvated and non-solvated states. The experimental data indicate that the change in standard free energy of the hydrophobic solvation is positive and so large that the solvation is incomplete even in the most dilute solutions studied. It is tentatively suggested that the hydrophobic solvation enhances the solubility in water of non-polar substances, and that the reason why non-polar groups in protein solutions are buried in the interior of the protein conformations is a low degree of solvation of these groups in the solvent exposed state.

Heat Capacities of Aqueous Solutions of Glutaric and Malonic Acids

Abstract Using a calorimeter composed of a Dewar vessel and a Beckmann thermometer, the specific heat capacities of aqueous solutions of glutaric and malonic acids were measured at 30 °C. Techniques for establishing the temperature gadient between the solution in the Dewar and the outer air bath were adopted. The partial molar heat capacities at infinite dilution were estimated assuming a relation of the form mφCp=bm+cm2. The contributions of the –CH2– and –COOH groups to the partial molar heat capacities in aqueous solution are roughly additive: for –CH2– a positive contribution and for –COOH a negative one. The Δ(=‾Cp2°–Cp2(pure state)) were also calculated and positive and negative values were obtained for Δ(–CH2–) and Δ(–COOH), respectively.

Heat capacities of aqueous electrolytes: eight 1:1 electrolytes and ΔCp0 for ionization of water at 298 K

We have made measurements with a flow calorimeter leading to apparent molal heat capacities of aqueous solutions of NaCl, HCl, KBr, KCl, KOH, NaBr, HBr, and NaOH at 298 K. Results have been used to derive apparent molal heat capacities of these electrolytes at infinite dilution and thence ΔCp0 = −215.2 ± 4 J K−1mol−1 for ionization of H2O(liq) at 298 K.

Heat capacity of aqueous solutions of sulfuric acid at low temperatures

Results of an experimental determination of the specific heat of H2O-H2SO4 solutions at low temperatures are presented and the heat capacity of a heterogeneous two-component system is analyzed.

Enthalpy of dilution and heat capacity of aqueous solutions of tetrabutylammonium butyrate as a function of temperature

Enthalpies of dilution of tetrabutylammonium butyrate are reported as a function of temperature between 10° and 50°C. Heat capacities of aqueous solutions of tetrabutylammonium butyrate were measured in order to obtain values ofφcp at 15°, 25°, and 35°C. These data were combined with the enthalpy of dilution data to obtain φcp as a function of molality and temperature. The apparent molal heat content φL decreased with increasing temperature in concentrated solutions but increased with increasing temperatures in dilute solutions (below0.7 m). Over the temperature range studied φcp shows a maximum as a function of molality at approximately 0.5m. The decrease in φcp with increasing concentration of hydrophobic solute is consistent with the view that the hydrophobic hydration cages, formed under the influence of the tetrabutylammonium and butyrate ions, are saturated at about 0.5m, and that at higher molalities increased overlap of the hydration cages occurs.

Heat Capacities of Aqueous Solutions of Ethylene Glycol, Propylene Glycol and 1, 3-Butanediol

A calorimerter composed of a Dewar vessel and a Beckmann thermometer was constructed. By means of this calorimeter, the heat capacities of aqueous solutions of ethylene glycol, propyrene glycol, and butanediol were measured at 30d C. It was confirmed by the measurement of heat capacities of n-heptane that the errors due to the evaporation were negligible. The partial molar heat capacities at the infinite dilution were obtained for the respective solutes. The structural changes of water caused by the dissolution of these solutes were discussed,

Heat capacity of solutions by flow microcalorimetry

A differential flow microcalorimeter has been designed for the measurement of heat capacities of solutions. Under steady-state condition, it is possible to obtain directly the ratio of the heat capacity of a solution to that of its solvent without any knowledge of the heat capacity of the instrument, the flow rate, or the induced change in temperature. The steady state is reached within 1 min. The overall precision on heat capacity changes is 0.5 per cent and the limit of detectability is 7 × 10 −5 JK −1 g −1 . As a check for reproducibility, the apparent molar heat capacities of aqueous solutions of NaCl in the range 0.01 to 2 mol kg −1 and of urea in the range 0.1 to 10 mol kg −1 were measured at 297.3 K.

The Activity Coefficients of Hydrofluoric Acid in Water from 0 to 35 °C.

The mean stoichiometric activity coefficients of hydrofluoric acid in aqueous solutions have been calculated from measurements of electrolytic conductivity, the electromotive forces of galvanic cells without liquid junction, and the freezing-point depression. Values obtained from freezing-point depressions were converted to values for 25 °C using known values of the heats of dilution and apparent molal heat capacities of aqueous solutions of hydrofluoric acid of various concentrations. It is also shown that values for the concentrations of the various ionic species in hydrofluoric acid, namely, H+, F-, , and HF depend on the functions used to represent the ionic activity coefficients whereas values of the mean activity, , are independent of such functions. Values of the pH of various concentrations of hydrofluoric acid are given for temperatures of 0 to 35 °C; these, likewise, are nearly independent of activity-coefficient function used to obtain values for the ionic concentrations.

Apparent molal heat capacities of aqueous solutions of alkali halides and alkylammonium salts

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTApparent molal heat capacities of aqueous solutions of alkali halides and alkylammonium saltsH. Rueterjans, F. Schreiner, U. Sage, and Th. AckermannCite this: J. Phys. Chem. 1969, 73, 4, 986–994Publication Date (Print):April 1, 1969Publication History Published online1 May 2002Published inissue 1 April 1969https://doi.org/10.1021/j100724a038RIGHTS & PERMISSIONSArticle Views172Altmetric-Citations78LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (909 KB) Get e-Alerts

Heat capacity changes and standard partial molal heat capacities of aqueous solutions of some tetra-alkyl ammonium halides at 30°C and the effect on water structure

ΔC°p values of tetra-alkylammonium halide salts Me4NBr, Me4NI, Et4NBr, Et4NI, Pr4 NBr, Pr4NI and Bu4NBr in aqueous solutions at 30°C have been determined by measuring integral heats of solution at 25 and 35°C ΔC°p values which vary from –16.5 to 179 cal deg.–1 mole–1 are in the increasing order of Me4NI < Me4NBr < Et4NBr ≃ Et4NI < Pr4NBr ≃ Pr4NI < Bu4NBr. Results are discussed in terms of the influence of tetra-alkylammonium halide salts on the water structure. Me4NBr and Me4NI break water structure, while all other tetra-alkylammonium bromide and iodide salts enhance or promote water structure. The influence of R4N+ salts in promoting water structure increases greatly with increase in the size of the alkyl group R. The influence of anions (bromide and iodide) does not appear to be significant in modifying the structure of water. Results from this work support the concept of “cation-cation interactions” in explaining the nature of interaction of tetra-alkylammonium halide salts with water.

THE HEAT CAPACITY OF AQUEOUS SOLUTIONS OF HYDROFLUORIC ACID

The heat capacity of aqueous solutions of hydrofluoric acid varying in concentration from 0.55 to 48% was determined over the temperature range 18° to 20 °C. The respective values for the specific heat varied between 0.996 and 0.718 cal. per gm. The values obtained are consistent among themselves but differ markedly from those found in the literature. The apparent molal heat capacity of the solute over this range of concentration and temperature was calculated and compared with values obtained from the data of other experimenters.

Heats of Dilution and Heat Capacities of Aqueous Solutions of Mono-, Di- and Trimethylamine Hydrochlorides1

Heats of Dilution and Heat Capacities of Aqueous Solutions of Mono-, Di- and Trimethylamine Hydrochlorides¹

A Study of the Heat Capacity of Aqueous Solutions of Urea and Mannite

A Study of the Heat Capacity of Aqueous Solutions of Urea and Mannite

A Study of the Heat Capacity of Aqueous Solutions of Barium Chloride

A Study of the Heat Capacity of Aqueous Solutions of Barium Chloride