Hydration Heat Capacity Research Articles

Heat capacities of hydration of saturated uncharged organic compounds at 25° C

The procedures so far adopted for interpreting the partial molal heat capacities at infinite dilution of organic compounds in water at 25°C, Φ°Cp, are critically reviewed and a new method of correlating Φ°Cp data to the molecular structure is proposed. In this method, the ΔChp values, obtained by substracting the heat capacities in the gas phase from the Φ°Cp data, are interpreted as the sum of the following terms: (i) formation of a cavity inside the solvent; (ii) interaction between the hydrocarbon part of the molecule and water; (iii) interaction between hydrophilic centres, Y, and water; (iv) a term to account for interactions among centres, Y, when more than one hydrophilic group is present in the molecule.A general equation which accounts for the formation of the cavity and for the interaction water–hydrocarbon surface is obtained on the basis of the ΔChp values of the first six n-alkanes. The values of the (iii)rd and (iv)th terms are then calculated for several types of groups Y and of couples Y1, Y2, by using the above mentioned equation in conjunction with the ΔChp values.This analysis has revealed that both the formation of the cavity and the hydrocarbon group combine to produce large positive Φ°Cp values, while all hydrophilic groups always bring about a decrease of the partial molal heat capacities. It is also shown that the interaction between hydrophilic centres in the same molecule is important in determining the Φ°Cp values, and that this may cause either ancrease or a decrease of the Φ°Cp values predicted on the basis of the Φ°Cp contribution for non-interacting groups.

The standard chemical free enthalpy, enthalpy, entropy and heat capacity of hydration of the hydrogen ion, and the surface potential of water at 25°C

AbstractThe standard chemical free enthalpy, enthalpy, entropy and heat capacity of hydration of the H+ ion have been determined. The determination is based on a cyclic process in which the ferricinium ion and the ferrocene molecule are involved.No rather arbitrary divisions or long‐range extrapolations of thermodynamic data for electroneutral combinations of ions have to be made in this method. The accuracy of the values obtained, especially of the entropy, is high, and is determined mainly by the accuracy of the experimental data. For the first time an estimate of the heat capacity of a single ion is given.From the value of the chemical free enthalpy of hydration obtained and literature data on the real free enthalpy of hydration, the surface potential of water can be calculated.If 1 atm fugacity and 1 molal concentration are used as standard states in the gas‐phase and the aqueous solution, respectively, the following values are obtained (at 25 °C):

Low Temperature Heat Capacity, Entropy and Heats of Formation and Hydration of Monocalcium Phosphate

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTLow Temperature Heat Capacity, Entropy and Heats of Formation and Hydration of Monocalcium PhosphateEdward P. Egan Jr., Zachary T. Wakefield, and Kelly L. ElmoreCite this: J. Am. Chem. Soc. 1956, 78, 9, 1811–1813Publication Date (Print):May 1, 1956Publication History Published online1 May 2002Published inissue 1 May 1956https://doi.org/10.1021/ja01590a009RIGHTS & PERMISSIONSArticle Views233Altmetric-Citations2LEARN 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 (411 KB) Get e-Alerts Get e-Alerts