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With a growing number of PCMs and new, suitable PCM candidates, an overview is not only important, but also increasingly complex. Classification of PCM was thus changed significantly in the past decades. A review of classification of PCMs from recent years shows that not only different classification criteria are used, but more important that they are often mixed, used inconsistently, even without a clear goal. Focusing on the main goal of current classification schemes, to give an overview of the material options for the search for new, suitable PCM candidates, including already established PCMs, a consistent classification is developed in a desktop study. For this, first, the general options for classification criteria are reviewed, and then the appropriate ones selected. Then, based on them a new, revised PCM classification is suggested. It is specifically detailed with regard to mixtures; for binary mixtures it is based on a literature review performed within the study. The result also stresses the importance of specific R&D: for pure substances the sources and the chemical modification, and for mixtures their optimization by new compositions, additives, etc. [ABSTRACT FROM AUTHOR]

With a growing number of PCMs and new, suitable PCM candidates, an overview is not only important, but also increasingly complex. Classification of PCM was thus changed significantly in the past decades. A review of classification of PCMs from recent years shows that not only different classification criteria are used, but more important that they are often mixed, used inconsistently, even without a clear goal. Focusing on the main goal of current classification schemes, to give an overview of the material options for the search for new, suitable PCM candidates, including already established PCMs, a consistent classification is developed in a desktop study. For this, first, the general options for classification criteria are reviewed, and then the appropriate ones selected. Then, based on them a new, revised PCM classification is suggested. It is specifically detailed with regard to mixtures; for binary mixtures it is based on a literature review performed within the study. The result also stresses the importance of specific R&D: for pure substances the sources and the chemical modification, and for mixtures their optimization by new compositions, additives, etc.

Students’ misconceptions in science can lead to a range of learning difficulties if the teacher does not choose the appropriate teaching strategies to reduce their frequency. In this paper, 13–14-year-old students’ misconceptions regarding structure and states of matter, pure substances, and mixtures are explored. The teaching strategy with E-learning material was applied to examine its effects on the frequency of misconceptions. The research was conducted in urban schools in Bosnia and Herzegovina with 7th- and 8th-grade students. Findings pointed to the misconceptions originating in transferring the macroscopic observations into the submicroscopic level and in misinterpretation of the size of particles. Students who used E-learning material at school mostly had lower percentages of misconceptions in comparison to students from the control group and students who accessed the same E-learning material from their home. This indicates that the E-learning strategy could have promising results if applied more extensively at schools. This study aims to direct teachers’ attention toward applying E-learning in chemistry teaching, for students to gain scientifically accepted knowledge and to reduce the occurrence of misconceptions.

In this work, the dynamic viscosity of Newtonian fluids is modeled using Eyring's theory and the residual Helmholtz free energy. In order to estimate this energy, a modified Peng-Robinson cubic equation of state is applied. The pseudo-experimental data have been obtained from two databases (DIPPR and NIST databses) most commonly used in the development of thermodynamic models, where DIPPR data are used to obtain the parameters and generalization of the model and the NIST data are used to evaluate the predictive capabilities of the generalization procedure. The adjustable parameters of the model have been determined from data in the liquid and vapor coexistence for n-alkanes and n-alcohols. Later these parameters have been generalized using simple mathematical expressions that depend on the molecular weight of each substance. The predictive capabilities of the model are evaluated in the liquid and vapor single-phases. The absolute deviations during the correlation process are below 3.27%, while in the prediction process they are below 5.60%. The generalized model is extended to binary mixtures using a simple mixture rule with one interaction parameter. The experimental data of the mixtures are obtained from different literature works and the absolute deviations are around 8.19% (without binary interaction coefficients) and 3.45% (with binary interaction coefficients). Finally, the model is compared with others in the literature using an analysis of variance in order to establish if there is a statistically significant difference between the deviations of the models used in the comparison. The statistical results show that the model developed in this work provides acceptable results. [ABSTRACT FROM AUTHOR]

The article studies the development of transfer measurement standards in the form of high-purity metals (Ag, Cd, Co, Cr, Cu, Fe, Ge, Mn, Mo, Ni, Pb, V, Zn). The evaluation of the mass fraction of the main component (MDOK) is performed by an indirect method (100 %o minus the sum of impurities). The impurity composition of the reference measurement standard materials was determined by mass spectrometry with inductively coupled plasma, reductive and oxidative melting using the State primary measurement standard of mass (molar) fraction and mass (molar) concentration of the component in liquid and solid substances and materials, based on coulometry, GET 176. The relative expanded uncertainty of MDOK (k = 2, P = 0,95) in the reference measurement standards was less, than 0,01 %o, in gravimetrically prepared solutions of the reference measurement standard it was less than 0,05 %o in most cases. The solutions of the reference measurement standards were used in the determination of certified values of metal mass fraction and mass concentration in reference materials for composition of mono-element solutions of approved types. The relative expanded uncertainty of certified values (k = 2, P = 0,95) of reference materials variedfrom 0,22 %o to 0,54 %o. Thus, it was demonstrated that metals can be used as reference measurement standards for storing a unit of the mass fraction of the main component and transferring it during characterization of reference materials for composition of solutions of the corresponding chemical elements. This work was performed within the research project «Research in the field of measurements of physicochemical composition and properties of substances, aimed at the development of State transfer measurement standards in the form of high-purity substances for reproduction and transfer of the units, characterizing chemical composition of solid substances» under the code «Purity» (2015-2017) and research and development project «Research in the field of measurements ofphysicochemical composition and properties of substances, aimed at the development of State transfer measurement standards in the form of high-purity substances for reproduction and transfer of the units, characterizing the chemical composition of solid substances and the development of reference measurement procedures» under the code «Purity-2» in the field of physicochemical measurements of composition and properties of inorganic components in solid substances (metals and salts) and food safety indicators under the code «Purity-2b» (2017-2019).

This paper presents the results of a series of studies aimed at investigating the reference material (RM) of a multicomponent solution. An algorithm for estimating the uncertainty induced by the chemical element content in the RM is proposed taking into account the mass of the measurand in each component of the mixture. The results calculated according to the preparation procedure using the proposed algorithm were confirmed by the Monte Carlo method, while the elemental content in the mixture was confirmed via inductively coupled plasma optical emission spectroscopy. The applicability of weighted mean estimates for characterizing an RM of a multicomponent solution is shown.

Analysis revealed, that in the area of chemical composition measurements high-purity substances may be regarded as the best measurement capabilities in the database of the International Bureau of Weights and Measures. Until now none of the countries of the world has the complete collection of high purity substances with evaluated purity level. At the present time the development of high-purity substances with evaluated values of mass fractions of the base substance is intensively going on to ensure metrological traceability to SI units using both primary methods and other instrumental methods of analysis.

The heat of vaporization of a pure substance at its normal boiling temperature is a very important property in many chemical processes. In this work, a new empirical method was developed to predict vaporization enthalpy of pure substances. This equation is a function of normal boiling temperature, critical temperature, and critical pressure. The presented model is simple to use and provides an improvement over the existing equations for 452 pure substances in wide boiling range. The results showed that the proposed correlation is more accurate than the literature methods for pure substances in a wide boiling range (20.3–722 K).

The problem of water determination in the creation of pure substances and new functional materials with a low moisture content is considered. The structure, metrological characteristics, and prospects of application of the state primary standard of mass fraction and mass (molar) concentration of water in solid and liquid substances and materials GET 173-2013 are presented. Examples of developing thermogravimetric and chemical analyses are provided. [ABSTRACT FROM AUTHOR]

In this work, a new generalized correlation for pure substances is proposed for the estimation of vapor pressure, applicable in wide temperature range. Was used equilibrium liquid-vapor data with 28 refrigerants and minimizing the sum of the squares of the relative deviation in liquid-vapour pressure were determined the parameters and constants characteristics of the new equation and generalized for any pure substance using the acentric factor. Vapor pressure predictions were made for 45 pure substances who they didn't not participate in the minimization, generated percent relative average deviation of 1.6073%. The results were compared with others equations for calculating the vapor pressure and the comparison indicates that the proposed method provide more accurate results than other methods used in this work. Finally, the calculations of enthalpies of vaporization were done with deviations of 0.880% and the Waring criterion was applied to check the constants presed in this paper. [ABSTRACT FROM AUTHOR]

• A thermal conductivity model is developed based on the analogy concept and is applied to pure substances. • Data are included for 24 organic families and 56 functional groups in a temperature range of 16.6 to 604.65 K and pressures below 4032 bar. • The final model presents one interaction parameter that is generalized using the group contribution technique. • Prediction of thermal conductivity in the saturation and single-phase conditions are done. • The model provides acceptable results when in comparison to other correlations. The aim of this work is to apply a group contribution method to describe the thermal conductivity of pure substances. The model has five adjustable parameters that have been generalized using the acentric factor, RT c /P c relation, and a contribution of each group in the substance through a tendency graphical analysis. The thermodynamical properties included in the model are estimated using a modified Peng-Robinson EoS. The proposed model is applied to 351 substances distributed into 160 for the correlation, 96 for testing, and 95 for predictive capabilities. The above includes 24 organic families and 56 functional groups. The average absolute deviations are below 6.51% for the liquid-vapor coexistence and below 7.93% for the one-phase condition. The overall results are compared to other literature works on saturation and single-phase conditions. These results show that the model provides acceptable values of deviations and can be used to describe different types of substances. Finally, three cases of study are done as an alternative to represent the alkanes, 1-alcohols, and water substances. The average absolute deviations for 1-alkanes and 1-alcohols are below 7.00% and for water is around 3.76%. In general, the generalized model can be used as an alternative to describe the thermal conductivities of pure substances in the saturation and single-phase conditions with acceptable results. A group contribution method to model the thermal conductivity of pure substances. Luis F. Cardona, Luis A. Forero and Jorge A. Velásquez. [Display omitted] [ABSTRACT FROM AUTHOR]

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Abstract: The heat of vaporization of a pure substance at its normal boiling temperature is a very important property in many chemical processes. In this work, a new empirical method was developed to predict vaporization enthalpy of pure substances. This equation is a function of normal boiling temperature, critical temperature, and critical pressure. The presented model is simple to use and provides an improvement over the existing equations for 452 pure substances in wide boiling range. The results showed that the proposed correlation is more accurate than the literature methods for pure substances in a wide boiling range (20.3–722K). [Copyright &y& Elsevier]

Abstract: A simple equation is presented for predicting the temperature dependence of the vapor-pressure of a pure substance along the entire (liquid+vapor) coexistence curve, from the triple point to the critical point. The proposed equation is based on the use of a dimensionless temperature reduced by using critical and triple point values, and of the Clausius–Clapeyron equation as a zeroth-order approximation. The pressure and temperature at the triple point, the normal boiling temperature, and the pressure and temperature at the critical point are required as input data. The proposed equation is verified for 53 fluids by using NIST data. These data are reproduced with an overall average deviation of 0.55%. [Copyright &y& Elsevier]

Abstract: We use the Clausius–Clapeyron equation to calculate third virial coefficients at low reduced temperatures. This procedure gives an alternative to predict third virial coefficients in a region where the third virial coefficient is difficult to measure. We compare the results of this method with published third virial coefficient data. Calculated third virial coefficients have average percentage deviations within 5% of the experimental values at reduced temperatures between 0.8 and 1.0. [Copyright &y& Elsevier]