Heat Capacities Of Organic Compounds Research Articles

Comparison of isochoric and isobaric heat capacities of liquid organic non-electrolytes and their vaporization enthalpies

The present paper is devoted to the study of the relationship between the difference of isochoric heat capacities of liquid and ideal gas phase organic non-electrolytes and their vaporization enthalpy at 298.15 K. This investigation is intended to more deeply analyze the origin of the recent finding that the difference of isobaric heat capacities of organic compounds in liquid and ideal gas phase is in a linear correlation with the vaporization enthalpy. We showed that the difference of isobaric and isochoric heat capacities of liquid aromatic compounds is constant within 3 J·K−1·mol−1 and does not depend on the vaporization enthalpy. A direct proportionality between isochoric heat capacity change and the vaporization enthalpy was established for 84 compounds, which included not only aromatic liquids but other rigid and relatively inflexible molecules (root-mean-square deviation equaled 2.5 J·K−1·mol−1). The slope agreed with that of isobaric heat capacity change – vaporization enthalpy correlation. Statistical significance of the established relationship far exceeded correlations with other molecular size-related parameters, namely the heat capacities, molar volume, and molecular weight.

The fusion thermochemistry of rubrene and 9,10-diphenylanthracene between 298 and 650 K: Fast scanning and solution calorimetry

The fusion enthalpies and the heat capacities of crystalline, molten, and supercooled liquid rubrene (Tm = 603 K) and 9,10-diphenylanthracene (Tm = 523 K) were measured using fast scanning calorimetry and conventional DSC. The experimental fusion enthalpies at the melting temperature were corrected to 298.15 K according to Kirchhoff’s law of thermochemistry. On the other hand, the fusion enthalpies at 298.15 K were determined from the solution enthalpies of these compounds in benzene, considering “like dissolves like” principle. The fusion enthalpies at 298.15 K obtained using independent methods were in mutual agreement. The heat capacity corrections of the fusion enthalpies of the studied non-planar polycyclic aromatic hydrocarbons to 298.15 K were found to be significantly higher than for planar polyaromatics.The features of measurement of the heat capacities of organic compounds by fast scanning calorimetry in the temperature range of notable volatility were discussed. The complete absence of the mass losses during heating-cooling cycles was found to be unnecessary condition for accurate heat capacity measurement; tolerable mass losses during the procedure were evaluated.

Quantitative Structure–Property Relationship Prediction of Liquid Heat Capacity at 298.15 K for Organic Compounds

Novel QSPR models were developed and evaluated for the prediction of heat capacity of liquids at 298.15 K with only three descriptors. Two linear and nonlinear models were produced using genetic function approximation (GFA) and adaptive neurofuzzy inference system (ANFIS) methods based on a data set of 706 compounds with a wide variety of functional groups. The results showed that both GFA and ANFIS methods could model the relationship between the liquid heat capacity of organic compounds and their structures with high accuracy. The predictive quality of the QSPR models were tested for an external test set, where the squared correlation coefficients of prediction for the GFA and ANFIS methods were 0.970 and 0.973, respectively.

Prediction of high pressure liquid heat capacities of organic compounds by a group contribution method

A new method for estimating high pressure liquid heat capacities based on molecular structure and group contribution is proposed. A common set of structural groups was employed. The method was developed using 67 sets of 43 organic compounds with 3449 experimental heat capacity data. A small number of measured compounds, data points per compound and other comparable methods were observed. This is a simple first-order approximation with acceptable accuracy of 2.548%.

Calculation of Entropy and Heat Capacity of Organic Compounds in the Gas Phase. Evaluation of a Consistent Method without Adjustable Parameters. Applications to Hydrocarbons

The purpose of this study has been to determine how well a consistent ab initio thermostatistical method reproduces experimental values of heat capacity and entropy. The method has been applied to calculation of heat capacity and entropy of a representative set of hydrocarbons that includes compounds consisting of multiple conformers. All Cp and S values are for the gaseous state at 1 atm; units are cal K-1 mol-1. A detailed sensitivity (error) analysis has been performed to determine the root mean square (rms) values of errors expected of the calculated values: these are 0.27 cal for Cp and 0.36 cal for entropy. In comparing calculated values with experimental values, it is necessary to consider also the uncertainties of the experimental data. When these are included, the expected rms values of Cp(experimental) - Cp(calculated) values at 298.15 K range from 0.21 to 0.73. For S(experimental) - S(calculated), they range from 0.36 to 0.72. Calculations with frequencies derived with the 6-31G(d,p) basis set and scaled by 0.91 yielded rms values for Cp(experimental) - Cp(calculated) of individual compounds from 0.14 to 0.84 cal and rms values for S(experimental) - S(calculated) of individual compounds from 0.07 to 1.11 cal. Calculated Cp values for 7 out of 16 compounds agree with experimental values within the rms uncertainty estimated for the compound, and 11 fall within twice that estimate. For entropy, the calculated values for 13 of 18 compounds agree with the very limited available experimental data within the rms estimated uncertainty for the compound, and 16 of 18 fall within twice the uncertainty.

Estimation of the Differential Molar Heat Capacities of Organic Compounds at Their Melting Point

Methods for the estimation of the differential molar heat capacity, the difference between the heat capacity of the solid and the liquid form of organic compounds at their melting point Δcp(Tm), are presented. Three schemes are considered: the first involves use of group contribution methods for the prediction of solid heat capacity (cpS) and liquid heat capacity (cpL); the other two, empirical correlations through the entropy of fusion at the melting point ΔSf(Tm). Recommendations for the different categories of organic compounds are made that provide substantial improvement over the commonly used assumption of Δcp = 0, in the prediction of ideal solid solubility and solid vapor pressure.

Saturated-liquid heat capacity of organic compounds: New empirical correlation model

A new saturated-liquid heat capacity model is recommended. This model is tested and compared with the known polynomial and quasi-polynomial models on 39 sets with 1453 experimental heat capacity data. The obtained results indicate that the new model is better then the existing models, especially near the critical point.

Heat Capacities of Organic Compounds in the Liquid State I. C1 to C18 1-Alkanols

Heat capacities of liquid C1 to C18 1-alkanols measured by calorimetric methods were compiled and evaluated. The selected experimental data were fitted as a function of temperature with cubic splines using weighted least squares minimization. The parameters of the cubic spline polynomials and the recommended values for heat capacities are presented. A new quasi-polynomial equation which permits extrapolation of heat capacities outside the temperature range of experimental values was derived and its parameters for C1 to C10 1-alkanols are presented.

Heat capacities of organic compounds in liquid state II. C1 to C18 n-alkanes

Heat capacities of liquid C1 to C18 n-alkanes measured by calorimetric methods have been compiled and evaluated. The selected experimental data were fitted as a function of temperature with cubic splines using weighted least squares minimization. The parameters of the cubic spline polynomials and the recommended values for heat capacities are presented. Heat capacities were also fitted by a quasipolynomial equation permitting extrapolation of heat capacities outside the temperature range of experimental values.

Accuracy of differential scanning calorimetry for heat capacities of organic compounds at high temperatures. New method for enthalpy of fusion by d.s.c.

Accuracy of differential scanning calorimetry for heat capacities of organic compounds at high temperatures. New method for enthalpy of fusion by d.s.c.

Additivity schemes permitting the estimation of partial molar heat capacities of organic compounds in aqueous solution

The available [Formula: see text] values for neutral organic compounds in aqueous solution can be fitted with useful precision by additivity schemes based on atomic, bond, or group contributions. For the set of 132 compounds these schemes require 11, 14, or 49 parameters and give weighted average deviations of 14, 9, or 6 J K−1 mol−1. For acyclic molecules the atomic contributions scheme permits chemically useful estimates of [Formula: see text] to be made for compounds of C, H, O, and N.

Apparent molal heat capacities of organic compounds in aqueous solution. Part 3.—ω-Amino acids and related compounds

Values of apparent molal heat capacities ΦCp in the range 23°–55°C, were determined by adiabatic calorimetry for the following amino acids: glycine, α-alanine, α-aminoisobutanoic acid, valine, serine, threonine, sarcosine, dimethylglycine, betaine, β-alanine, β- and γ-aminobutanoic acids, δ-aminopentanoic acid and Iµ-aminohexanoic acid. Some hydroxy acids, sodium and ammonium salts of carboxylic acids, methyl and ethyl esters of acetic acid and glycine methylester hydrochloride have also been studied.An attempt has been made to quantify the contribution to ΦCp associated with charge separation in amphionic molecules by comparing the experimental value (ΦexpCp) for amino acids with those for similar uncharged molecules (ΦrefCp). The ΔΦ* values (ΦexpCp–ΦrefCp) thus obtained for +H3N(CH2)m COO– compounds (m= 2, 3, 4, 5) are used in order to obtain some information about the interactions between neutral or charged amino and carboxylic groups. Effects connected with the methyl additions to N+ centres in glycine or ammonium salts are considered.

Heat capacities of organic compounds in solution. I. Low-molecular-weight alcohols in water

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTHeat capacities of organic compounds in solution. I. Low-molecular-weight alcohols in waterEdward M. Arnett, W. B. Kover, and J. V. CarterCite this: J. Am. Chem. Soc. 1969, 91, 15, 4028–4034Publication Date (Print):July 1, 1969Publication History Published online1 May 2002Published inissue 1 July 1969https://doi.org/10.1021/ja01043a002RIGHTS & PERMISSIONSArticle Views357Altmetric-Citations98LEARN 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 (843 KB) Get e-Alerts Get e-Alerts

Estimation of Heat Capacity of Organic Compounds from Group Contributions

Estimation of Heat Capacity of Organic Compounds from Group Contributions

The heat capacities of organic compounds at low temperatures. iii. an adiabatic calorimeter for heat capacities at low temperatures

1. I. An adiabatic calorimeter for heat capacities at low temperatures has been devised which gives results consistent to about 1 2 per cent. 2. 2. It is faster and simpler in operation, more economical than the present most used type and applicable to a wider range of organic compounds because of its small size (8 cc.). 3. 3. The heat of fusion of toluene was found to be 1584 calories/mol. at 177.94° K. 4. 4. The heat capacity of touluene was found from 100° K. to 250° K. by comparison with benzene.

The heat capacities of organic compounds at low temperatures. II. A low temperature thermostat. Thousandth degree copper-constantan thermocouple reference tables from 85° to 310° K

The heat capacities of organic compounds at low temperatures. II. A low temperature thermostat. Thousandth degree copper-constantan thermocouple reference tables from 85° to 310° K