James S. Chickos

Reference materials for calorimetry and differential thermal analysis

This publication is the result of the efforts of the ICTAC working group “thermochemistry” 1 during 1997–1998. It deals with reference materials (in abbreviated form: RM) for calorimetry and differential thermal analysis. It represents the updated version of two previous documents produced by the IUPAC Commission “Physicochemical Measurements and Standards”: the first was published in Pure and Applied Chemistry in 1974 [1] and the second in the book entitled “Recommended Reference Materials for the Realization of Physicochemical Properties” [2]. Calorimetry and differential thermal analysis are applicable to a wide range of scientific and technological research fields involving physical, chemical and biological processes. Calorimetry usually yields highly reproducible results which may, however, be inaccurate because of faulty calibration of the measurement system. Calibration is a fundamental requirement for every thermoanalytical study. It requires the establishment of a quantitatively defined relationship between the value indicated by the measuring instrument and the correct value. The calibration of a modern calorimeter is achieved by the quantification of the produced

Enthalpies of Sublimation of Organic and Organometallic Compounds. 1910–2001

A compendium of sublimation enthalpies, published within the period 1910–2001 (over 1200 references), is reported. A brief review of the temperature adjustments for the sublimation enthalpies from the temperature of measurement to the standard reference temperature, 298.15 K, is included, as are recently suggested values for several reference materials. Sublimation enthalpies are included for organic, organometallic, and a few inorganic compounds.

Enthalpies of Vaporization of Organic and Organometallic Compounds, 1880-2002

A compendium of vaporization enthalpies published within the period 1910–2002 is reported. A brief review of temperature adjustments of vaporization enthalpies from temperature of measurement to the standard reference temperature, 298.15 K, is included as are recently suggested reference materials. Vaporization enthalpies are included for organic, organo-metallic, and a few inorganic compounds. This compendium is the third in a series focusing on phase change enthalpies. Previous compendia focused on fusion and sublimation enthalpies. Sufficient data are presently available for many compounds that thermodynamic cycles can be constructed to evaluate the reliability of the measurements. A protocol for doing so is described.

Critically evaluated thermochemical properties of polycyclic aromatic hydrocarbons

Experimental thermochemical properties of benzene, toluene, and 63 polycyclic aromatic hydrocarbons, published within the period 1878–2008 (over 350 references), are reported. Available experimental data for the enthalpies of combustion used to calculate enthalpies of formation in the condensed state, combined with sublimation, vaporization, and fusion enthalpies, are critically evaluated. Whenever possible, recommended values for these thermochemical properties and for the enthalpies of formation in the gas state at T=298.15K are provided.

Heat capacity corrections to a standard state: a comparison of new and some literature methods for organic liquids and solids

The estimation methods commonly used to correct phase change enthalpies to the standard state are compared where possible to experimental measurements. Heat capacity corrections for liquid-gas equilibria are found to correlate with molecular structure, and we suggest an improved method for estimating these corrections using group methods. A similar improvement for estimating heat capacity corrections for solid-gas equilibria using group methods is also proposed. Heat capacity corrections for liquid-solid equilibria are examined. These corrections were found to be comparable in magnitude to the experimental error associated with heat capacity measurements, so it was not possible to obtain any meaningful correlations.

A Group Additivity Approach for the Estimation of Heat Capacities of Organic Liquids and Solids at 298 K

A group additivity method is described which provides heat capacity estimates of the condensed phase. The data base consists of 810 liquids and 446 solids. Group values for carbon in various common substitution and hybridization states and for 47 functional groups are provided. The standard error of estimation using this approach on this data base is 19.5 (liquids) and 26.9 J/ (mole K) (solids). This can be compared to typical experimental uncertainties of 8.12 and 23,4 J/ (mole K) associated with these measurements, respectively. Experimental uncertainties were estimated from the numerical differences obtained for a given substance from multiple independent literature reports.

Phase Transition Enthalpy Measurements of Organic and Organometallic Compounds. Sublimation, Vaporization and Fusion Enthalpies From 1880 to 2010

Article on phase transition enthalpy measurements of organic and organometallic compounds, sublimation, and vaporization and fusion enthalpies from 1880 to 2010.

Estimating Solid-Liquid Phase Change Enthalpies and Entropies

A group additivity method based on molecular structure is described that can be used to estimate solid–liquid total phase change entropy (Δ0TfusStpce) and enthalpy (Δ0TfusHtpce) of organic molecules. The estimation of these phase changes is described and numerous examples are provided to guide the user in evaluating these properties for a broad range of organic structures. A total of 1858 compounds were used in deriving the group values and these values are tested on a database of 260 additional compounds. The absolute average and relative errors between experimental and calculated values for these 1858 compounds are 9.9 J⋅mol−1⋅K−1 and 3.52 kJ⋅mol−1, and 0.154 and 0.17 for Δ0TfusStpce and Δ0TfusHtpce, respectively. For the 260 test compounds, standard deviations of ±13.0 J⋅mol−1⋅K−1(Δ0TfusStpce) and ±4.88 kJ mol−1(Δ0TfusHtpce) between experimental and calculated values were obtained. Estimations are provided for both databases. Fusion enthalpies for some additional compounds not included in the statistic...

Determination of vaporization enthalpies of simple organic molecules by correlations of changes in gas chromatographic net retention times

A technique is described for determining vaporization enthalpies Δg1Hm(298 K) of organic compounds by high resolution gas chromatography. The technique correlates changes in net retention times of compounds whose Δg1Hm(298 K) are known with those of the compound(s) of interest. The best results are obtained when the reference compounds are structurally similar and in the same chemical family. Application to hydrocarbons and various hydrocarbon derivatives containing one functional group is documented in this report. Comparison with literature values of 102 compounds resulted in a standard deviation of 1.27 kJ mol−1. In most cases, the difference between the literature value and the value from our results is within the normal errors associated with vaporization enthalpy determinations. A linear correlation between the logarithms of experimental vapor pressure and reciprocal retention time was also observed for the compounds studied.

Sublimation enthalpies at 298.15 K using correlation gas chromatography and differential scanning calorimetry measurements

The sublimation enthalpies of 17 hydrocarbons are obtained by combining the technique of correlation gas chromatography (CGC), to evaluate vaporization enthalpies at 298.15 K, and differential scanning calorimetry (DSC) to measure fusion enthalpies. Vaporization enthalpies at 298.15 K obtained by CGC are compared to values measured directly from vapor pressure measurements at temperatures above the melting point by adjusting the experimental vaporization enthalpy for the effects of temperature. Vaporization enthalpies obtained by these two methods agree within3877 J mol ˇ1 . Fusion enthalpies are similarly adjusted for temperature. Sublimation enthalpies, obtained by combining temperature adjusted fusion, and vaporization enthalpies agree within2580 J mol ˇ1 . The sublimation enthalpies of azulene and 1,8-cyclotetradecadiyne are also measured by head-space analysis resulting in values of 76880 and 94348 J mol ˇ1 at 298.15 K, respectively. # 1998 Elsevier Science B.V.