Publications

Abstract The standard (p degrees = 0.1 MPa) molar energies of combustion in oxygen, at T= 298.15 K, of two crystalline bis(N,N-diethylthioureas) R(CONHCSNEt2)(2): pyridine-2,6-dicarbonyl-bis(N,N-diethylthiourea), R = pyridyl. abbreviated as (bis-py-DETU). and adipoyl-dicarbonyl-bis(N,N-diethylthiourea), R = (CH2)(4), abbreviated as (bis-ad-DETU). were measured by rotating bomb calorimetry so, the standard molar enthalpies of formation of both compounds, in their crystalline phase, were derived. [GRAPHICS] Furthermore, the energetics of the title compounds were studied by means of density functional theory Calculations at the B3LYP/6-311G(dp) level of theory.

Abstract The standard (p = 0.1 MPa) molar enthalpies of combustion in oxygen of five N-thenoylthiocarbamic-O-n-alkylesters, C4H3SCO-NHCSOR, R = Et (Httee), n-Pr (Httpe), n-Bu (Httbe), n-Pen (Httpene), and n-Hex (Htthe), were measured, at T = 298.15 K, by rotating-bomb calorimetry. The standard molar enthalpies of sublimation of these compounds were determined using Calvet microcalorimetry. These values were used to derive the standard molar enthalpies of formation of the title compounds, in their crystalline and gaseous phases, respectively. Furthermore, differential scanning calorimetry was applied in order to measure the temperatures and enthalpies of fusion for all compounds. Entropies of fusion were derived from the experimental results and the odd and even effect was found. [GRAPHICS]

Abstract Batch processes were carried out for the photocatalytic degradation of Acid Red 151 from its aqueous solution using ZnO catalyst at different initial dye concentrations. The process was found to be diffusion controlled for the first 15-20 minutes (before irradiation) with an average diffusion coefficient of 6.759 × 10 -6 cm 2/s. The photocatalytic degradation kinetics was analyzed using the first order, second order and Langmuir-Hinshelwood expressions by linear and non-linear method. The four types of second order kinetic and Langmuir-Hinshelwood kinetic models were also discussed. Non-linear method is a better way to obtain the kinetic parameters. The photocatalytic degradation process was found to follow first order kinetics at lower substrate concentrations and second order kinetics at higher substrate concentrations. © 2007 Science & Technology Network, Inc.

Abstract A new mini-bomb combustion calorimeter designed at the University of Lund was improved, installed and calibrated at the University of Porto. This calorimeter is suitable for high precision combustion calorimetry with samples of mass about (10 to 40) mg. The energy equivalent of the calorimeter, = (1946.45 +/- 0.11) J center dot K-1, was obtained from 15 independent calibration experiments with benzoic acid SRM 39i. Anthracene, succinic acid, acetanilide, and 1,2,4-triazole were used as test compounds, with excellent agreement with the literature values. [GRAPHICS]

Abstract This letter explains the appropriate way to calculate the parameters in pseudo first and second order kinetics, Langmuir and Freundlich isotherm.

Abstract The energetics of the C-F, C-Cl, C-Br, and C-I bonds in 2-haloethanols was investigated by using a combination of experimental and theoretical methods. The standard molar enthalpies of formation of 2-chloro-, 2-bromo-, and 2-iodoethanol, at 298.15 K, were determined as Delta(f)(ClCH2CH2OH, l) = -315.5 +/- 0.7 kJ center dot mol(-1), Delta(f)(BrCH2CH2OH, l) = -275.8 +/- 0.6 kJ center dot mol(-1), Delta(f)(ICH2CH2OH, l) = -207.3 +/- 0.7 kJ center dot mol(-1), by rotating-bomb combustion calorimetry. The corresponding standard molar enthalpies of vaporization, Delta(vap)(ClCH2CH2OH) = 48.32 +/- 0.37 kJ center dot mol(-1), Delta(vap)(BrCH2CH2OH) = 54.08 +/- 0.40 kJ center dot mol(-1), and Delta(vap)(ICH2CH2OH) = 57.03 +/- 0.20 kJ center dot mol(-1) were also obtained by Calvet-drop microcalorimetry. The condensed phase and vaporization enthalpy data lead to Delta(f)(ClCH2CH2OH, g) = -267.2 +/- 0.8 kJ center dot mol(-1), Delta(f)(BrCH2CH2OH, g) = -221.7 +/- 0.7 kJ center dot mol(-1), and Delta(f)(ICH2CH2OH, g) = -150.3 +/- 0.7 kJ center dot mol(-1). These values, together with the enthalpy of selected isodesmic and isogyric gas-phase reactions predicted by density functional theory (B3LYP/cc-pVTZ) and CBS-QB3 calculations were used to derive the enthalpies of formation of gaseous 2-fluoroethanol, Delta(f)(FCH2CH2OH, g) = -423.6 +/- 5.0 kJ center dot mol(-1), and of the 2-hydroxyethyl radical, Delta(f)(CH2CH2OH, g) = -28.7 +/- 8.0 kJ center dot mol(-1). The obtained thermochemical data led to the following carbon-halogen bond dissociation enthalpies: DHo(X-CH2CH2OH) = 474.4 +/- 9.4 kJ center dot mol(-1) (X = F), 359.9 +/- 8.0 kJ center dot mol(-1) (X = Cl), 305.0 +/- 8.0 kJ center dot mol(-1) (X = Br), 228.7 +/- 8.1 kJ center dot mol(-1) (X = I). These values were compared with the corresponding C-X bond dissociation enthalpies in XCH2COOH, XCH3, XC2H5, XCHCH2, and XC6H5. In view of this comparison the computational methods mentioned above were also used to obtain Delta(f)(FCH2COOH, g) = -594.0 +/- 5.0 kJ center dot mol(-1) from which DHo(F-CH2COOH) = 435.4 +/- 5.4 kJ center dot mol(-1). The order DHo(C-F) > DHo(C-Cl) > DHo(C-Br) > DHo(C-I) is observed for the haloalcohols and all other RX compounds. It is finally concluded that the major qualitative trends exhibited by the C-X bond dissociation enthalpies for the series of compounds studied in this work can be predicted by Pauling's electrostatic-covalent model.

Abstract The results are analyzed in terms of structural contribution to the standard molar enthalpies of formation. The metal-ligand exchange enthalpies in the crystalline phase show that the increase of the ester-alkyl chain length does not significantly affect the difference between the metal to ligand and the hydrogen to ligand binding enthalpies, [D(M-L) - D(H-L)].

Abstract The study of Chemical Equilibrium is a central and inevitable point for knowledge acquiring in Chemistry. However, it is here where students do present more alternative conceptions becoming more difficult for them to understand it and thus a great challenge for the teaching. As something abstract, that includes non observable events, multiple factors, advanced reasoning and complex microscopic interpretation, this is one of the topics in the Chemistry curriculum that appeals more to the use of computational simulations for its teaching. We have carried out studies using a computer programme for the teaching of chemical equilibrium which confirm the usefulness of these digital tools. Computational simulations are very useful and rich context educational resources. Webquests may be supporting material in the exploration of a computational simulation: they are a kind of an "exploration guide" and at the same time a way of creating students' nearby contexts. There are several advantages that come from the use of this work dynamic using the Web.

Abstract A monitoring program of pesticides was implemented in the "ZV1" vulnerable zone (Directive 91/676/EEC) in Portugal, in order to assess the impact of intensive horticulture practices on groundwater contamination. The monitoring network comprised 23 sampling points sampled every 3 months during a 2-year period. Forty-two pesticides belonging to varied chemical families, including current pesticides, persistent organic pollutants (POPs), and degradation products, were analyzed by solid-phase microextraction (SPME) and gas chromatography with electron-capture detection-thermoionic specific detection (GC-ECD-TSD) or mass spectrometry (GC-MS). Statistical treatment was performed by descriptive analysis followed by chemometric multivariate analysis. The latter included cluster analysis, linear discriminant analysis, and factor analysis. Twenty-two pesticides were quantitated, 20 pesticides were not detected, and metalaxyl, benalaxyl, quinalphos, pirimicarb, and prometryn were only qualitatively detected. The most frequently detected pesticides (% of samples analyzed) were lindane (53%), pendimethalin (49%), endosulfan sulfate (44%), and endosulfan (38%) while those that most frequently exceeded the 0.1 mu g L-1 European Union (EU) limit were pendimethalin (13%), endosulfan (12%), endosulfan sulfate (11%), and atrazine (9%). 45% of the samples exceeded the EU limit for individual pesticides while 27% exceeded the limit set to the sum of pesticides (0.5 mu g L-1). Principal component analysis revealed five principal components that were attributed to environmental/agrochemical managing factors. The broad range of pesticides investigated combined with the intensive character of the local agriculture contributed to the diversity of pesticides that were detected. However, the frequency of pesticides above the EU regulatory limit is comparable to that found in the literature concerning different Portuguese and European regions.