Index of content:
Volume 20, Issue 6, November 1991

A New Equation of State and Tables of Thermodynamic Properties for Methane Covering the Range from the Melting Line to 625 K at Pressures up to 100 MPa
View Description Hide DescriptionThis work reviews the data on thermodynamic properties of methane which were available up to the middle of 1991 and presents a new equation of state in the form of a fundamental equation explicit in the Helmholtz free energy. A new strategy for optimizing the structure of empirical thermodynamic correlation equations was used to determine the functional form of the equation. The Helmholtz function containing 40 fitted coefficients was fitted to selected experimental data of the following properties: (a) thermal properties of the single phase (pρT) and (b) of the liquid‐vapor saturation curve (p _{ s }ρ’ρ‘) including the Maxwell criterion, (c) speed of soundw, (d) isochoric heat capacityc _{ v }, (e) isobaric heat capacityc _{ p }, (f) difference of enthalph Δh, and (g) second virial coefficient B. Independent equations are also included for the vapor pressure, the saturated liquid and vapor densities, the isobaric ideal gas heat capacity and the meltingpressure as functions of temperature. Tables for the thermodynamic properties of methane from 90 K to 620 K for pressures up to 1000 MPa are presented. For the density, uncertainties of ±0.03% for pressures below 12 MPa and temperatures below 350 K and ±0.03% to ±0.15% for higher pressures and temperatures are estimated. For the speed of sound, the uncertainty ranges from ±0.03% to ±0.3% depending on temperature and pressure.Heat capacities may be generally calculated within an uncertainty of ±1%. To verify the accuracy of the new formulation, the calculated property values are compared with selected experimental results and existing equations of state for methane. The new equation of state corresponds to the new International Temperature Scale of 1990 (ITS‐90) and is extrapolable up to pressures of 20000 Mpa.

Thermodynamic Properties of the Aqueous Sulfuric Acid System to 350 K
View Description Hide DescriptionExperimental measurements for aqueous sulfuric acid and its related pure, solid phases have been thermodynamicallyanalyzed and correlated as a function of temperature and composition from pure water to pure acid. The pure phases included anhydrous sulfuric acid, five of its hydrates and ice. Experimental data which were used in the correlation included measurements of the enthalpy of dilution, both solution and pure phase heat capacities, electromotive force and solution freezing points. The correlation yielded mutually consistent expressions for the Gibbs energy of each phase and these functions generally reproduce the experimental data to ±0.75 percent. The Gibbs energy functions of the pure solid phases were used to generate tables of their thermodynamic properties from 0 K to the melting points. The Gibbs energy function for aqueous sulfuric acid was used to produce tables of both integral and partial molar solution properties as a function of sulfuric acid mole fraction every 50° from 200 to 350 K.

The Solubility of Carbon Dioxide in Water at Low Pressure
View Description Hide DescriptionThe system carbon dioxide‐water is of great scientific and technological importance. Thus, it has been studied often. The literature for the solubility of carbon dioxide in water is vast and interdisciplinary. An exhaustive survey was conducted and approximately 100 experimental investigations were found that reported equilibrium data at pressures below 1 MPa. A model based on Henry’s law was used to correlate the low pressure data (those up to 1 MPa). The following correlation of the Henry’s constants (expressed on a mole fraction basis) was developed ln(H _{2} _{1}/MPa)=−6.8346+1.2817×10^{4}/T−3.7668×10^{6}/T ^{2} +2.997×10^{8}/T ^{3} The correlation is valid for 273<T<433 K(0<t<160 °C) where T is in K. Any experimental data that deviated significantly from this model were duly noted.

Chemical Kinetic Data Sheets for High‐Temperature Reactions. Part II
View Description Hide DescriptionRate coefficient measurements for over fifty gas‐phase bimolecular reactions were critically evaluated and compared to theoretical calculations. The results of this work are summarized here in forty‐nine Data Sheets, one sheet for each reaction or set of reactions of a single pair of reagents. The reactions chosen are of interest in propulsion, combustion, and atmospheric chemistry. Each Data Sheet consists of two pages that include a brief resumé of the important experimental measurements and theoretical calculations, a graphical presentation of the data, a recommended rate coefficient expressed as a function of temperature, k(T)=A T ^{ n }exp(−B T), with probable uncertainty limits, a discussion of the basis for the recommendation, an equilibrium constant and a rate coefficient for the reverse reaction where applicable, and pertinent references.

Atomic Weights of the Elements 1989
View Description Hide DescriptionThe biennial review of atomic weight, A__{r}(E), determinations, and other cognate data has resulted in changes for nickel from 58.69±0.01 to 58.6934±0.0002 and for antimony from 121.75±0.03 to 121.757±0.003 due to new calibrated measurements. Because the measurement of the isotopic composition of mercury has also been improved during the last two years, the Commission was able to reduce the uncertainty of the atomic weight of this element from 200.59±0.03 to 200.59±0.02. Due to the nearly constant isotopic composition of protactinium in nature, where ^{2} ^{3} ^{1}Pa is the predominant isotope, the atomic weight of this element was fixed to 231.03588±0.000 02. The Table of Isotopic Compositions of the Elements 1989 will be published as a companion paper to that on Atomic Weights of the Elements 1989. The Table of Standard Atomic Weights Abridged to Five Significant Figures and current data on isotopic compositions of nonterrestrial material are included to benefit users who are more concerned with the length of time during which a given table has full validity to the precision limit of their interest. The Table of Atomic Weights to Four Significant Figures was prepared and has been published separately.

Isotopic Compositions of the Elements 1989
View Description Hide DescriptionThe Subcommittee for Isotopic Abundance Measurements (SIAM) of the IUPAC Commission on Atomic Weights and Isotopic Abundances has carried out its biennial review of isotopic compositions, as determined by mass spectrometry and other relevant methods. The Subcommittee’s critical evaluation of the published literature element by element forms the basis of the Table of Isotopic Compositions of the Elements as Determined by Mass Spectrometry 1989, which is presented in this Report. Atomic Weights calculated from the tabulated isotopic abundances are consistent with A _{ r }(E) values listed in the Table of Standard Atomic Weights 1989.