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Law Constant (law + constant)

Distribution by Scientific Domains
Chemistry16%

Kinds of Law Constant

  • henry law constant
    		•

    Selected Abstracts

    Determination of physicochemical properties of tetrabromobisphenol A

    ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 12 2008
    Hidetoshi Kuramochi
    Abstract Aqueous solubility (Sw), 1-octanol/water partition coefficient (KOW), and vapor pressure of the nonionic form of 2,2,,6,6,-tetrabromo-4,4,-isopropylidenediphenol (tetrabromobisphenol A or TBBP-A) were measured. From this, enthalpies of solution and vaporization were estimated. Furthermore, enthalpy of fusion and melting point were measured to estimate subcooled liquid vapor pressure, the infinite dilution activity coefficient, and Henry's law constant. Since TBBP-A is expected to exit in both ionic and nonionic forms at near neutral pH, pH effects on physicochemical properties were also examined. Because of the ionization of TBBP-A, Sw increased by five orders of magnitude, while KOW decreased by eight orders of magnitude. Furthermore, an analytical model based on mass balance and dissociation of TBBP-A was applied to represent the pH dependence. [source]

    Modeling polycyclic aromatic hydrocarbon composition profiles of sources and receptors in the Pearl River Delta, China,

    ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 1 2008
    Chang Lang
    Abstract Changes in concentration profiles of polycyclic aromatic hydrocarbons (PAHs) from emission sources to various environmental media in the Pearl River Delta, China were investigated using fugacity modeling under steady state assumption. Both assumed evenly and observed unevenly distributed PAH moles emission profiles were applied. Applicability of the fugacity model was validated against the observed media PAH concentrations and profiles. At equal emission rates, the differences of media concentrations among various PAHS were as high as three (air) to seven (soil and sediment) orders of magnitude. Dramatic changes of PAH profiles from emission sources to various bulk environmental media also were demonstrated by using the actual emission rates. In general, the fractions of higher molecular weight PAHs in air and water were much lower than those at the emission sources, although the PAH profiles in soil and sediment were characterized by a significant reduction of lower molecular weight PAHs. It is likely that the field-measured median concentration profiles cannot be adopted directly for source apportionment without rectification. The most influential parameters affecting PAH profiles in the study area were emission rates, degradation rates, adsorption coefficient, Henry's law constant, PAH concentrations in upstream surface water, fugacity ratio, vapor pressure, and diffusion coefficient in air. [source]

    The long-term fate of polychlorinated biphenyls in San Francisco Bay (USA)

    ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 10 2004
    Jay A. Davis
    Abstract A simple one-box mass budget model is presented as a first step toward a quantitative understanding of the long-term fate of polychlorinated biphenyls (PCBs) in San Francisco Bay (USA). Sensitivity analysis indicated that the most influential input parameters were degradation half-life in sediment, Kow, outflow, average PCB concentration in sediment, and depth of the active sediment layer. Moderately influential parameters included organic carbon content of suspended solids, sediment burial mass transfer coefficient, and Henry's law constant. If external loading could be eliminated entirely, the mass of PCBs in the bay is predicted to drop to half of the present value in 20 years. The model predicts that sustained loading of 10 kg year,1 would prevent the total PCB mass in the bay from ever dropping below 10% of the present mass. With a sustained loading of 20 kg year,1, the model predicts that the total PCB mass would never fall below about 25% of the present mass. The half-lives in the bay for the individual PCB congeners evaluated in this report ranged from four years for PCB 18 to 30 years for PCB 194. [source]

    Harbor seals (Phoca vitulina) in British Columbia, Canada, and Washington State, USA, reveal a combination of local and global polychlorinated biphenyl, dioxin, and furan signals

    ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 1 2004
    Peter S. Ross
    Abstract The harbor seal (Phoca vitulina) can serve as a useful indicator of food web contamination by persistent organic pollutants (POPs) because of its high trophic level, wide distribution in temperate coastal waters of the Northern Hemisphere, and relative ease of capture. In 1996 through 1997, we live-captured 60 harbor seal pups from three regions, spanning remote (Queen Charlotte Strait, BC, Canada), moderately industrialized (Strait of Georgia, BC, Canada), and heavily industrialized (Puget Sound, WA, USA) marine basins straddling the Canada-United States border. Biopsy samples of blubber were taken and analyzed for congener-specific polychlorinated biphenyls (PCBs), polychlorinated dibenzo- p -dioxins (PCDDs), and polychlorinated dibenzofurans (PCDFs) by using high-resolution gas chromatography-high-resolution mass spectrometry. Harbor seals in Puget Sound were heavily contaminated with PCBs, whereas seals from the Strait of Georgia had relatively high concentrations of PCDDs and PCDFs. Pattern evaluation and principal components analysis suggested that proximity to sources influenced the mixture to which seals were exposed, with those inhabiting more remote areas being exposed to lighter PCB congeners (those with lower Henry's law constant and KOW) that disperse more readily through atmospheric and other processes. Total toxic equivalents to 2,3,7,8-tetrachlorodibenzo- p -dioxin for the PCBs, PCDDs, and PCDFs suggest that Puget Sound seals are at greatest risk for adverse health effects, and that PCBs represent the class of dioxinlike contaminants of greatest concern at all sites. [source]

    Estimating the probability of bird mortality from pesticide sprays on the basis of the field study record

    ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 7 2002
    Pierre Mineau
    Abstract The outcome of avian field studies was examined to model the likelihood of mortality. The data were divided into clusters reflecting the type of pesticide application and bird guilds present on site. Logistic regression was used to model the probability of a bird kill. Four independent variables were tested for their explanatory power: a variable reflecting acute oral toxicity and application rate; a variable reflecting the relative oral to dermal toxicity of the pesticides; Henry's law constant; and a variable reflecting possible avoidance of contaminated food items, the hazard factor (HF). All variables except for HF significantly improved model prediction. The relative dermal to oral toxicity, especially, was shown to have a major influence on field outcome and clearly must be incorporated into future avian risk assessments. The probability of avian mortality could be calculated from a number of current pesticide applications and the conclusion was made that avian mortality occurs regularly and frequently in agricultural fields. [source]

    Using measured octanol-air partition coefficients to explain environmental partitioning of organochlorine pesticides

    ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 5 2002
    Mahiba Shoeib
    Abstract Octanol-air partition coefficients (Koa) were measured directly for 19 organochlorine (OC) pesticides over the temperature range of 5 to 35°C. Values of log Koa at 25°C ranged over three orders of magnitude, from 7.4 for hexachlorobenzene to 10.1 for 1,1-dichloro-2,2-bis (p-chlorophenyl) ethane. Measured values were compared to values calculated as KowRT/H (where R is the ideal gas constant [8.314 J mol,1 K,1], T is absolute temperature, and H is Henry's law constant) were, in general, larger. Discrepancies of up to three orders of magnitude were observed, highlighting the need for direct measurements of Koa. Plots of Koa versus inverse absolute temperature exhibited a log-linear correlation. Enthalpies of phase transition between octanol and air (,Hoa) were determined from the temperature slopes and were in the range of 56 to 105 kJ mol,1 K,1. Activity coefficients in octanol (,o) were determined from Koa and reported supercooled liquid vapor pressures (p), and these were in the range of 0.3 to 12, indicating near-ideal solution behavior. Differences in Koa values for structural isomers of hexachlorocyclohexane were also explored. A Koa -based model was described for predicting the partitioning of OC pesticides to aerosols and used to calculate particulate fractions at 25 and ,10°C. The model also agreed well with experimental results for several OC pesticides that were equilibrated with urban aerosols in the laboratory. A log-log regression of the particle-gas partition coefficient versus Koa had a slope near unity, indicating that octanol is a good surrogate for the aerosol organic matter. [source]

    Measurement of Henry's law constant for methyl tert -butyl ether using solid-phase microextraction

    ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 8 2001
    Britta G. Bierwagen
    Abstract Increasing groundwater contamination with methyl tert -butyl ether (MTBE) requires more efficient remediation technologies. Accurate measurement of MTBE's air,water partitioning coefficient (Henry's law constant, H) is important for the design and optimization of removal efficiency for many treatment systems as well as for predicting its fate and transport. Previously published data for MTBE appear to have some unusual nonlinearity at lower temperatures (15,30°C), and a wide range of values exists for dimensionless H at 25°C, from 0.0216 to 0.1226 in the published literature. We measured H for MTBE using headspace solid-phase microextraction (SPME) and a static method that considers equilibrium partitioning in a closed system, for temperatures between 15 and 40°C. To validate our methods, we measured H for benzene, toluene, and trichloroethylene and compared our results to previously published values, with excellent agreement. The Arrhenius plot for MTBE indicates that ln(HMBTE) = 6.85,2,900 T,1, with T in K. At 25°C, HMBTE = 0.0555 ± 0.0122. [source]

    Modeling nanoporosity development in polymer films for low-k applications

    POLYMER ENGINEERING & SCIENCE, Issue 5 2005
    Prathamesh Doshi
    The bubble growth dynamics of a polymer supersaturated with CO2 have been modeled for micron-size films after nucleation. The model equations are based on the shell model of Arefmanesh, Advani, and Michaelides in which a nucleated bubble is surrounded by a finite concentric shell of polymer supersaturated with gas. Bubbles grow by mass transfer of dissolved gas from this shell. The model is extended to allow for diffusion of dissolved gas out of the shell in addition to diffusion into the bubble. A parametric analysis is performed to examine the effects of film thickness, temperature, diffusivity at the Tg and Henry's law constant. POLYM. ENG. SCI., 45:640,651, 2005. © 2005 Society of Plastics Engineers [source]

    Direct Volumetric Measurement of Gas Oversolubility in Nanoliquids: Beyond Henry's Law

    CHEMPHYSCHEM, Issue 12 2009
    Marc Pera-Titus Dr.
    Abstract The properties of condensed matter are strongly affected by confinement and size effects at the nanoscale. Herein, we measured by microvolumetry the increased solubility of H2 in a series of solvents (CHCl3, CCl4, n -hexane, ethanol, and water) when confined in the cavities of mesoporous solids (,-alumina, silica, and MCM-41). Gas/liquid solubilities are enhanced by up to 15 times over the corresponding bulk values for nanoliquid sizes smaller than 15 nm as long as gas/liquid interfaces are mesoconfined in a porous network. Although Henry's law constant apparently no longer applies under these confinement, the concentration of dissolved H2 still increases linearly with increasing pressure in the range 1,5 bar. We discuss the role and main implications of surface excess concentrations at mesoconfined gas/liquid interfaces in enhancing gas solubility. [source]

    Estimations of vapor pressure and activity coefficients in water and octanol for selected aromatic chemicals at 25°C

    ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 11 2000
    Sum Chi Lee
    Abstract A roupcontribution method is developed to estimate the supercooled liquid vapor pressure and the activity coefficients in water and octanol at 25°C of 98 selected monoaromatic compounds, many of which are or have been produced as chlorinated by-products in the manufacture of pulp and paper. The set includes alkylphenols, chlorinated phenols, anisoles, catechols, cymenes, guaiacols, syringols, and veratroles. The method can be used to estimate vapor pressures, solubilities in water, octanol-water partition coefficients, octanol-air partition coefficients, and Henry's law constants. It can also be used for predicting these partition coefficients as well as solubilities and vapor pressures for these and structurally similar compounds. [source]

    Method for predicting solubilities of solids in mixed solvents

    AICHE JOURNAL, Issue 5 2009
    Martin E. Ellegaard
    Abstract A method is presented for predicting solubilities of solid solutes in mixed solvents, based on excess Henry's law constants. The basis is statistical mechanical fluctuation solution theory for composition derivatives of solute/solvent infinite dilution activity coefficients. Suitable approximations are made for a single parameter characterizing solute/solvent interactions. Comparisons with available data show that the method is successful in describing a variety of observed mixed solvent solubility behavior, including nearly ideal systems with small excess solubilities, systems with solute-independent excess solubilities, and systems deviating from these simple rules. Successful predictions for new solvent mixtures can be made using limited data from other mixtures. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source]