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This paper presents the calculation method allowing one to obtain the matched magnitudes of critical parameters of hydrocarbon gases with an accuracy comparable to the errors of the experimental methods. The ratios obtained allow an assessment of the values of the critical temperature, critical pressure, critical volume, acentric factor, and compressibility in the homologous series of alkanes up to C 100 . The critical parameters for alkanes 4 < n C < 40 calculated using formulas presented in the article demonstrated good consistency with the experimental data. The proposed values of critical constants for normal alkanes can be used to calculate the physiochemical properties of the compounds, while the calculation methods can be used to determine the critical constants of hydrocarbon components of other homologous series.

IntroductionSystematic comparative analysis of temperature dependences of thermodynamic potentials within a broad range of concentrations and temperatures is used to calculate the excess thermodynamic functions of crystals and glasses required to create the physicochemical model of oxide systems (silicate, borate, germanate, etc.) and to compare the resulting thermodynamic data with the structure of compounds. The enthalpy of formation and standard entropy are the key characteristics of synthesis of new construction materials needed for the high-tech fields of space and nuclear power industries. However, the properties of many silicates, the essential components of these materials, have not been studied to the full extent. The reason is that the thermodynamic properties of sodium, potassium, and lithium silicates given in reference books [1][2][3] significantly differ due to characteristics of the methods used for processing and estimating the calorimetric data. If no reliable criterion for choosing the proper value is suggested, the accuracy of calculations performed using these data is rather doubtful [4, 5]. Thus, the initial data that can be used to determine the thermodynamic properties of alkali metal silicates in a condensed state for K 2 SiO 3 and K 2 Si 2 O 5 are given in [3], while the experimental and calculated thermodynamic data for K 2 SiO 3 , Li 2 SiO 3 , Li 2 Si 2 O 5 , Na 2 SiO 3 , and Na 2 Si 2 O 5 are presented in [1]. Hence, currently there is no unified matched database of thermodynamic data suitable for creating an adequate physicochemical model that would include silicate and borate.

Processes of surface and underground water forming in the Khibiny massif have been studied using a physical-chemical model of the "water-rock-atmosphere-organic substance" system. The obtained model solutions are indicative of the fact that formation of surface and underground water of the Khibiny massif takes place on the whole in the framework of the considered system without attracting a hypothetical outside source of pollutants. The results are of practical and methodological importance for assessment of prediction of the man-induced impact on water systems in conditions of Subarctic.