The conditions under which the Picker flow microcalorimeter can be used to measure enthalpies and rates of reactions were investigated. For this purpose, systematic studies were made of the enthalpies of neutralization of HCl, HBr, HNO 3 , acetic, proprionic, and butyric acids with NaOH, enthalpies of hydrolysis of methyl and ethyl acetate with NaOH, and the reaction rates of the ester hydrolysis with NaOH. The general procedure and various sources of error are discussed and it is concluded that enthalpies of slow reactions can be measured to about 1% when the calorimeter is operated in the quasi-isothermal mode and the reaction rates to about 3% when operated in the quasi-adiabatic mode.

A series of measurements with aqueous electrolyte and nonelectrolyte solutions indicates that there is a small systematic difference between the heat capacities per unit volume determined with a Picker flow microcalorimeter and the original prototype. Through various tests and comparisons, it is, concluded that the commercial instrument gives results closer to the true values. Most of the previous data obtained in our laboratory have been corrected and expressed relative to aqueous NaCl at 25°C taken as a standard.

Heats of mixing at 25°C have been obtained calorimetrically for alkane mixtures where component 1 is cyclohexane, 2,2-dimethylbutane or n-hexane and component 2 is a normal-Cn, n= 6,8,12 or 16, or a corresponding branched-Cn: 2,2-dimethylbutane, 2,2,4-trimethylpentane, 2,2,4,6,6-penta-methylheptane or 2,2,4,4,6,8,8-heptamethylnonane. For the three n-Cn series, the molar heats and heats per unit volume are positive and increase rapidly with n. With the branched-Cn, cyclohexane gives smaller positive heats decreasing with n, while n-hexane and 2,2-dimethylbutane show increasingly negative heats. The magnitudes and variations of the heats, and of the derived X12 parameters are inconsistent with the usual interpretation of positive ΔHM in n-alkane mixtures, i.e. an energetic weakness of methyl(end)-methylene (middle) interactions. The results are explained by energetic effects associated with a correlation of molecular orientations (CMO) in the pure components and the mixture. The CMO, studied optically by Bothorel and collaborators, is highly sensitive to molecular shape, increasing with n for pure n-Cn liquids, remaining zero for the branched-Cn, and being destroyed on mixing with spherical molecules such as cyclohexane and 2,2-dimethylbutane. Parameters (J), characterizing the CMO in the component liquids, are used to give a quantitative interpretation of the X12 and ΔHM values.

A precision densimeter for liquids, based on the oscillating-tube principle, has been designed. The apparatus allows relative density measurements to be carried out routinely with ppm precision, on 5–7 cm3 of solution, in a total time ranging between 5 to 10 min. The results of various tests reported here show the densimeter to be useful for investigation in aqueous as well as nonaqueous media; it is particularly well adapted to accurate measurements of small density increments, as required in excess-volume studies. Since the instrument operates in the flow regime, it is also adaptable to on-line monitoring of density in continuous processes.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPrecise closed-loop thermostatPatrick Picker , Carmel Jolicoeur , and Jacques E. Desnoyers Cite this: J. Chem. Educ. 1968, 45, 9, 614Publication Date (Print):September 1, 1968Publication History Received3 August 2009Published online1 September 1968Published inissue 1 September 1968https://doi.org/10.1021/ed045p614Request reuse permissionsArticle Views37Altmetric-Citations11LEARN 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 (584 KB) Get e-Alertsclose Get e-Alerts