Aqueous nonelectrolyte solutions — Part XX: Formula of structure I methane hydrate, congruent dissociation melting point, and formula of the metastable hydrate

2003 ◽  
Vol 81 (12) ◽  
pp. 1443-1450 ◽  
Author(s):  
David N Glew
Keyword(s):  
Melting Point ◽  
Equilibrium Constant ◽  
Methane Hydrate ◽  
Equilibrium Constants ◽  
Stability Range ◽  
Congruent Melting Point ◽  
Quadruple Point ◽  
Dissociation Equilibrium ◽  
Metastable Structure ◽  
The Stability

Sixteen new measurements of high precision for structure I methane hydrate with water between 31.93 and 47.39 °C are shown to be metastable and exhibit higher methane pressures than found by earlier workers. Comparison of earlier measurements between 26.7 and 47.2 °C permit positive identification of the structure II and the structure I hydrates. Forty-nine equilibrium constants Kp(h1[Formula: see text]l1g) for dissociation of structure I methane hydrate into water and methane, 32 between –0.29 and 26.7 °C for the stable hydrate and 17 between 31.93 and 47.39 °C for the metastable hydrate, are best represented by a three-parameter thermodynamic equation, which indicates a standard error (SE) of 0.63% on a single Kp(h1[Formula: see text]l1g) determination. The congruent dissociation melting point C(h1l1gxm) of metastable structure I methane hydrate is at 47.41 °C with SE 0.02 °C and at pressure 505 MPa. The congruent equilibrium constant Kp(h1[Formula: see text]l1g) is 102.3 MPa with SE 0.2 MPa. ΔH°t(h1[Formula: see text]l1g) is 62 281 J mol–1 with SE 184 J mol–1, and the congruent formula is CH4·5.750H2O with SE 0.059H2O. At the congruent point, ΔV(h1[Formula: see text]l1g) is zero within experimental precision, and its estimate is 1.3 with SE 1.6 cm3 mol–1. The stability range of structure I methane hydrate with water extends from quadruple point Q(s1h1l1g) at –0.29 °C up to quadruple point Q(h1h2l1g) at 26.7 °C, and its metastability range with water extends from 26.7 °C up to the congruent dissociation melting point C(h1l1gxm) at 47.41 °C. Key words: methane hydrate, clathrate structure I, metastability range, dissociation equilibrium constant, formula, congruent melting point, metastability of structure I hydrate.

Aqueous nonelectrolyte solutions. Part XIX. Congruent dissociation melting point and the formula of structure II methane hydrate

2003 ◽  
Vol 81 (2) ◽  
pp. 179-185 ◽  
Author(s):  
David N Glew
Keyword(s):  
Melting Point ◽  
Standard Error ◽  
Pressure Measurement ◽  
Methane Hydrate ◽  
Equilibrium Constants ◽  
Congruent Melting ◽  
Stability Range ◽  
Congruent Melting Point ◽  
Quadruple Point ◽  
Dissociation Equilibrium

Twenty-four equilibrium pressures, P(h2l1g), of structure II methane hydrate h2 with water l1 between 27.0 and 46.9°C are well represented by a four-parameter equation, which indicates a standard error (SE) of 1.95% on a single pressure measurement. Forty equilibrium constants Kp(h2[Formula: see text]l1g) for dissociation of structure II methane hydrate into water and methane between 27.0 and 47.7°C and at pressures up to 784 MPa at 45.0°C are best represented by a three-parameter thermodynamic equation, which indicates an SE 1.25% on a single Kp(h2[Formula: see text]l1g) determination. The congruent dissociation melting point C(h2l1gxm) of structure II methane hydrate is at 47.71°C with SE 0.03°C and at pressure 533 MPa with SE 5 MPa. The congruent Kp(h2[Formula: see text]l1g) is 102.9 with SE 0.3 MPa, ΔH°t(h2[Formula: see text]l1g) is 61 531 with SE 244 J mol–1, and the congruent formula is CH4·5.670H2O with SE 0.061H2O. At congruent point ΔV(h2[Formula: see text]l1g) = 0 and its estimate is 1.0 with SE 1.6 cm3 mol–1. Stability range of structure II methane hydrate with water extends from quadruple point Q(h1h2l1g) at 26.7°C and 55.5 MPa up to quadruple point Q(h2h3l1g) at 47.3°C and 620 MPa. The metastability range of structure I methane hydrate with water is discussed.Key words: methane hydrate, clathrate structure II, stability range, dissociation equilibrium constant, formula, congruent melting point, metastability of structure I hydrate.

scholarly journals Role of dimerization in the control of the functioning of the human haemoglobin mutant haemoglobin Howick (β37 Trp→Gly)

1994 ◽  
Vol 300 (2) ◽  
pp. 553-556 ◽  
Author(s):  
T Brittain
Keyword(s):  
Equilibrium Constant ◽  
Equilibrium Constants ◽  
Oxygen Affinity ◽  
Amino Acid Side Chain ◽  
Oxygen Binding ◽  
Dimerization Constant ◽  
Equilibrium Studies ◽  
Human Haemoglobin ◽  
Dissociation Equilibrium ◽  
Wide Range

Haemoglobin Howick shows a high oxygen affinity (p50 = 1 mmHg) and a low co-operativity (n = 1.3). Equilibrium studies show the protein to be essentially totally dimeric in the oxygenated form. A wide range of rapid kinetic experiments indicate that the deoxygenated form of the protein exists in a tetramer<-->dimer equilibrium with an associated equilibrium constant of 3 microM. These kinetic data also indicate that the oxygenated form of the protein exists in a tetramer<-->dimer equilibrium with an associated equilibrium constant of 35 mM, and furthermore clearly identifies a large increase in the rate of the tetramer-to-dimer dissociation process as the origin of the vastly increased dissociation equilibrium constants. Simulations of the protein-concentration-dependence of the oxygen-binding properties of haemoglobin Howick, based on the measured equilibrium parameters, closely fits the experimental data. The change in dimerization constant for the deoxygenated form of the protein corresponds remarkably well to the free-energy change predicted for the simple transfer of the amino acid side chain at position beta 37 from a hydrophobic to a hydrophilic environment during the dimerization process.

Aqueous nonelectrolyte solutions. Part XVI. Formula of deuterium sulfide D-hydrate and its dissociation thermodynamic functions

2000 ◽  
Vol 78 (1) ◽  
pp. 1-9 ◽  
Author(s):  
Colin W Clarke ◽  
David N Glew
Keyword(s):  
Heat Capacity ◽  
Thermodynamic Functions ◽  
Standard Enthalpy ◽  
Approximate Formula ◽  
Deuterium Oxide ◽  
Equilibrium Constants ◽  
Hydrate Dissociation ◽  
Quadruple Point ◽  
Dissociation Equilibrium ◽  
Heat Capacity Changes

A method has been devised to approximate both the hydrate formula number n and the standard thermodynamic functions for hydrate dissociation from the temperature change of the hydrate former fugacity along a univariant three-phase (hl1g) equilibrium line. Thermodynamic equations are derived, their validity discussed, and an iterative method for their solution is described. The univariant (hl1g) equilibrium dissociation of deuterium sulfide D-hydrate (D2S·nD2O phase h) into gaseous deuterium sulfide (g) and liquid deuterium oxide (l1) has been treated to give approximate formulae and dissociation constants at 58 temperatures from 2.798 to 30.666°C. Dissociation equilibrium constants Kp(h–> l1g) have been represented as a function of temperature by a four-parameter equation which yields both values and standard errors (i) for ΔHot(h–> l1g) and ΔCpot(h–> l1g) the standard enthalpy and heat capacity changes for D-hydrate dissociation and (ii) for n = r the approximate formula number of the D-hydrate at each experimental temperature. The formula D2S·6.115D2O with standard error 0.018D2O is found for deuterium sulfide D-hydrate at lower quadruple point Q(hs1l1g) 3.392°C; an approximate formula D2S·5.840D2O with SE 0.019D2O is found at upper quadruple point Q(hs1l2g) 30.770°C. Key words: clathrate D-hydrate of deuterium sulfide, deuterium sulfide D-hyfrate, formula of deuterium sulfide D-hydrate, thermodynamics of clathrate hydrate dissociation, dissociation equilibrium constant of deuterium sulfide D-hydrate, standard enthalpy, and heat capacity changes for dissociation of deuterium sulfide D-hydrate.

Aqueous nonelectrolyte solutions. Part XVIII. Equilibrium pressures of two methane hydrates with water. Formulae and dissociation thermo -dynamic functions for the structures I and II methane hydrates

2002 ◽  
Vol 80 (4) ◽  
pp. 418-439 ◽  
Author(s):  
David N Glew
Keyword(s):  
Standard Enthalpy ◽  
Pressure Measurement ◽  
Methane Hydrate ◽  
Equilibrium Constants ◽  
Methane Hydrates ◽  
Hydrate Dissociation ◽  
Quadruple Point ◽  
Methane Gas ◽  
Thermodynamic Equation ◽  
Parameter Equation

Literature data for the saturation pressure P(hl1g) of methane hydrate with water, at 102 temperatures between –0.29 and 46.87°C, are properly represented by two distinct equations, with a quadruple point Q(h1h2l1g) transition temperature at 26.7°C with standard error (SE) 0.9°C and 55.5 MPa with SE 5.3 MPa. The structure I type methane hydrate phase h1 is stable below 26.7°C and the structure II type methane hydrate phase h2 is stable above 26.7°C. Between –0.29 and 25.54°C, 85 equilibrium pressures of methane hydrate with water are best represented, with SE 1.33% on a single pressure measurement, by a four-parameter thermodynamic equation. The corresponding equilibrium methane fugacities are represented, with SE 0.94% on a fugacity determination, by a five-parameter equation. Between 26.98 and 46.87°C, 17 equilibrium methane hydrate pressures with water are best represented, with SE 2.22% on a pressure measurement, by a three-parameter equation. Composition of the equilibrium aqueous phase is evaluated using methane fugacity with the solubility equation including a Poynting correction. Literature data between –2.22 and –14.10°C, for the saturation pressure P(h1s1g) of structure I methane hydrate with ice, are properly represented by a two-parameter equation, with SE 1.1% on a single pressure measurement. Standard enthalpy change for structure I methane hydrate dissociation into ice and methane gas is found to be ΔHot(h1[Formula: see text] s1g) = 18058 J mol–1 with SE 608 J mol–1 at -8.28°C. The quadruple point Q(h1s1l1g) is estimated at –0.290°C with SE 0.0064°C and at 2.527 MPa with SE 0.053 MPa. Using the classical thermodynamic method, as described for deuterium sulfide D-hydrate, methane hydrate equilibrium fugacities define 85 equilibrium constants Kp(h1[Formula: see text]l1g) between –0.29 and 25.54°C for dissociation of structure I hydrate h1 into liquid water l1 and methane gas. Temperature dependence of ln Kp(h1[Formula: see text]l1g) is well-represented by a three-parameter thermodynamic equation that gives both estimates and their standard errors for (i) ΔHot(h1[Formula: see text]l1g) and ΔCpot(h1[Formula: see text]l1g), the standard enthalpy and heat capacity changes, respectively, for hydrate h1 dissociation, and for (ii) n = r, the approximate formula number of the hydrate CH4·nH2O at each experimental temperature. The formula CH4·6.205H2O with SE 0.066H2O is found for the structure I methane hydrate h1 with water at quadruple point Q(h1s1l1g) –0.29°C; an approximate formula CH4·5.759H2O with SE 0.077H2O is found at quadruple point Q(h1h2l1g) 26.7°C. Between 26.98 and 46.87°C, the 17-equilibrium constants Kp(h2[Formula: see text]l1g) for dissociation of structure II methane hydrate h2 into liquid water l1 and methane gas are represented by a constrained three-parameter thermodynamic equation. For structure II methane hydrate the formula CH4·5.822H2O with SE 0.064H2O is found at quadruple point Q(h1h2l1g) 26.7°C and the formula CH4·5.699H2O with SE 0.064H2O at 46.87°C. Molar volumes and cohesive energy densities of the methane hydrates are compared with equilibrium compressed water.Key words: clathrate hydrates of methane, two methane gas hydrates, formula of structure I methane hydrate, thermodynamics of clathrate hydrate dissociation, dissociation equilibrium constants of structure I methane hydrate, standard enthalpy and heat capacity changes for dissociation of structure I methane hydrate, methane hydrates' transition temperature, formula of structure II methane hydrate, dissociation equilibrium constants of structure II methane hydrate, standard enthalpy change for dissociation of structure II methane hydrate, methane hydrates' cohesive energy density.

Extraction of strontium and barium salts by the nitrobenzene solution of dicarbolide in the presence of glymes

1985 ◽  
Vol 50 (3) ◽  
pp. 581-599 ◽  
Author(s):  
Petr Vaňura ◽  
Emanuel Makrlík
Keyword(s):  
Stability Constants ◽  
Organic Phase ◽  
Equilibrium Constants ◽  
Minor Role ◽  
Nitrobenzene Solution ◽  
Ligand Structure ◽  
Stability Constants Of Complexes ◽  
Separation Factors ◽  
The Stability ◽  
A Minor

Extraction of microamounts of Sr2+ and Ba2+ (henceforth M2+) from the aqueous solutions of perchloric acid (0.0125-1.02 mol/l) by means of the nitrobenzene solutions of dicarbolide (0.004-0.05 mol/l of H+{Co(C2B9H11)2}-) was studied in the presence of monoglyme (only Ba2+), diglyme, triglyme, and tetraglyme (CH3O-(CH2-CH2O)nCH3, where n = 1, 2, 3, 4). The distribution of glyme betweeen the aqueous and organic phases, the extraction of the protonized glyme molecule HL+ together with the extraction of M2+ ion and of the glyme complex with the M2+ ion, i.e., ML2+ (where L is the molecule of glyme), were found to be the dominating reactions in the systems under study. In the systems with tri- and tetraglymes the extraction of H+ and M2+ ions solvated with two glyme molecules, i.e., the formation of HL2+ and ML22+ species, can probably play a minor role. The values of the respective equilibrium constants, of the stability constants of complexes formed in the organic phase, and the theoretical separation factors αBa/Sr were determined. The effect of the ligand structure on the values of extraction and stability constants in the organic phase is discussed.

Mucosal gastrin receptor. III. Regulation by gastrin

1980 ◽  
Vol 238 (2) ◽  
pp. G135-G140 ◽  
Author(s):  
K. Takeuchi ◽  
G. R. Speir ◽  
L. R. Johnson
Keyword(s):  
Serum Gastrin ◽  
Binding Capacity ◽  
Specific Binding ◽  
Equilibrium Constants ◽  
Biological Response ◽  
Liquid Diet ◽  
Regulatory Process ◽  
Membrane Preparation ◽  
Gastrin Receptor ◽  
Dissociation Equilibrium

Specific binding of 125I-labeled gastrin to rat gastric mucosal membranes was found to vary with serum gastrin levels. The dissociation equilibrium constants were not significantly different between receptor preparations. However, the binding capacities of the membrane preparations were directly correlated with serum gastrin levels. Fasting, feeding a liquid diet, and antrectomy significantly decreased serum gastrin and the concentrations of the gastrin receptor. Treatment of fasted and liquid-fed animals with pentagastrin prevented the decrease in receptors. Vagotomy increased both binding capacity and serum gastrin levels. These data indicate that gastrin stimulates the production of its own receptor. The upregulation of the gastrin receptor was evident if the binding capacity was expressed per milligram of protein, per microgram of DNA, or per amount of 125I-labeled choleragen bound to the same membrane preparation. This indicates that the biological response to gastrin is controlled in part by the regulation of the number of gastrin receptors present and that gastrin plays a role in this regulatory process.

scholarly journals Influence of the Al content on the phase transformations in Cu-Al-Ag alloys

2003 ◽  
Vol 28 (1) ◽  
pp. 33-38 ◽  
Author(s):  
A. T. Adorno ◽  
A. V. Benedetti ◽  
R. A. G. da Silva ◽  
M. Blanco
Keyword(s):  
Thermal Analysis ◽  
Differential Thermal Analysis ◽  
Transition Temperature ◽  
Phase Transformations ◽  
Decomposition Reaction ◽  
Phase Decomposition ◽  
Stability Range ◽  
X Ray ◽  
Al Content ◽  
The Stability

The influence of the Al content on the phase transformations in Cu-Al-Ag alloys was studied by classical differential thermal analysis (DTA), optical microscopy (OM) and X-ray diffractometry (XRD). The results indicated that the increase in the Al content and the presence of Ag decrease the rate of the <FONT FACE=Symbol>b</font>1 phase decomposition reaction and contribute for the raise of this transition temperature, thus decreasing the stability range of the perlitic phase resulted from the b1 decomposition reaction.

SOME EQUILIBRIUM CONSTANTS OF TRANSITION METAL HALIDES

1960 ◽  
Vol 38 (10) ◽  
pp. 1827-1836 ◽  
Author(s):  
M. W. Lister ◽  
P. Rosenblum
Keyword(s):  
Ionic Strength ◽  
Transition Metal ◽  
Equilibrium Constant ◽  
Spectrophotometric Method ◽  
Equilibrium Constants ◽  
Cell Voltage ◽  
Metal Halides ◽  
Complex Ions ◽  
Anomalous Variation ◽  
A Cell

Measurements are reported on the formation of complex ions in solutions containing cupric and chloride or bromide ions, and solutions of nickel or cobalt with chloride. In each case the halide was present in very low amount. With copper a spectrophotometric method was used, and a cell voltage method with nickel and cobalt. The ionic strength was kept constant, but the temperature was varied. The data show difficulties of interpretation if it is assumed that only MX+ ions (M is the metal, X is the halogen) are formed, the difficulties arising from the anomalous variation of the equilibrium constant with temperature, and from the general drift of the calculated constants from the e.m.f. measurements. Various explanations are considered and it is shown that postulation of M2X+3 ions is at least a possible explanation.

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