Influência do meio reacional no comportamento fotoquímico do inseticida paration etílico

The photodegradation of parathion in natural and dezionised waters was studied under irradiation at two different wavelengths: 280 nm and 313 nm. The influence of humic acids was evaluated. The results demonstrated that the degradation occurred only due to photochemical processes. The chemical hydrolysis and biological processes can be neglected in this case. The addition of humic acids did not increase the photodegradation rate in either water samples (natural or dezionised). In alkaline solutions the photodegradation rate was higher in dezionised water when compared to natural waters. The kinetic degradation in all experiments obeyed a first order reaction pattern.

Efeito da temperatura no desempenho catalítico de óxidos de ferro contendo cobre e alumínio

Aluminum and copper doped hematite was evaluated in the high temperature shift (HTS) reaction at several temperatures in order to find catalysts that can work in different operational conditions. It was found that the catalysts work in kinetic regime in the range of 300-400 ºC. Both copper and aluminum increases the activity and selectivity. Aluminum acts as textural promoter whereas copper acts as structural one. The most promising catalyst is that with both copper and aluminum which showed higher activity and selectivity than a commercial sample. This catalyst has the advantages of being non toxic and can work at low temperatures.

O estado vítreo dentro da perspectiva do curso de graduação em química (físico-química)

We consider the relevance of the study of the glassy state properties and the glass transition as important topics of the physical chemistry for undergraduate courses of Chemistry. Two of the most important theoretical approaches for the description of the glassy state, the thermodynamic and the kinetic models, are summarized with emphasis on the physical chemistry aspects. Examples illustrating the glass transition of some materials are also presented.

Descomposicion termica del diperoxido de pinacolona (3,6-diterbutil-3,6-dimetil-1,2,4,5-tetraoxaciclohexano) en solución de 2-metoxietanol

The thermal decomposition reaction of pinacolone diperoxide (DPP; 0.02 mol kg-1) in 2-methoxyethanol solution studied in the temperature range of 110.0-150.0 °C, follows a first-order kinetic law up to at least 50% DPP conversion. The organic products observed were pinacolone, methane and tert-butane. A stepwise mechanism of decomposition was proposed where the first step is the homolytic unimolecular rupture of the O-O bond. The activation enthalpy and activation entropy for DPP in 2-methoxyethanol were calculated (deltaH# = 43.8 ± 1.0 kcal mol-1 and deltaS# = 31.9 ± 2.6 cal mol-1K-1) and compared with those obtained in other solvents to evaluate the solvent effect.

Efeito da aplicação foliar de ácidos graxos na "Via das Lipoxigenases" de plantas de soja

The involvement of lipoxygenase isozymes in several physiological processes of plants has been described but their role is not well understood and more biochemical studies are needed to elucidate the role of the "Lipoxygenase Pathway" in plant physiology. Thus, the biochemical and kinetic characterization of a lipoxygenases "pool" from soybean leaves was carried out. Two genotypes were used: IAC-100 (a normal variety having lipoxygenases in the seeds) and IAC-100 TN (genetically modified genotype, which is devoid of lipoxygenases in the seeds). The plants were submitted to the application of fatty acids (lipoxygenase substrates) on leaves. The results of the biochemical and kinetic studies of lipoxygenase isozymes from leaves of the two genotypes analysed showed that genetic removal of lipoxygenase from seeds did not affect the response of the plant to the treatment, since both genotypes showed similar results.

A quimiluminescência como ferramenta analítica: do mecanismo a aplicações da reação do luminol em métodos cinéticos de análise

Relevant aspects of proposed mechanisms of the chemiluminescent reaction of luminol are presented and commented to emphasize its perspectives for kinetic analysis. A careful search for analytical applications of this reaction is discussed in order to point out new trends of the studies. Kinetic analysis using the luminol reaction is proposed to be a very attractive due to the good performance of the reaction in analytical applications and the positive characteristics of kinetic analysis, such as low cost and sensibility. It is pointed out that kinetic analysis using the chemiluminescent reaction of luminol should be encouraged.

Um experimento com propostas múltiplas para um laboratório de química geral

This article suggests a sequence of experiments on the preparation, analysis and some photochemical aspects of potassium tris (oxalato) ferrate(III) trihydrate. The sequence of experiments could be carried out in four or five 4-hour laboratory periods. The new part of this article is related to the kinetics studies involving the ambient illumination as well as the use of the cellophane paper of different colors as light filters. The aspects such as quantum yield, light absorption and photochemical reactions are explored in order to illustrate the relationships between the exposure time, light intensity and wavelength range on the photochemical reactions.

Reaction Kinetics and Viscosity Modelling in the Fusion Syntheses of Ca- and Ca/Mg-resinates

Rosin is a natural product from pine forests and it is used as a raw material in resinate syntheses. Resinates are polyvalent metal salts of rosin acids and especially Ca- and Ca/Mg- resinates find wide application in the printing ink industry. In this thesis, analytical methods were applied to increase general knowledge of resinate chemistry and the reaction kinetics was studied in order to model the non linear solution viscosity increase during resinate syntheses by the fusion method. Solution viscosity in toluene is an important quality factor for resinates to be used in printing inks. The concept of critical resinate concentration, c crit, was introduced to define an abrupt change in viscosity dependence on resinate concentration in the solution. The concept was then used to explain the non-inear solution viscosity increase during resinate syntheses. A semi empirical model with two estimated parameters was derived for the viscosity increase on the basis of apparent reaction kinetics. The model was used to control the viscosity and to predict the total reaction time of the resinate process. The kinetic data from the complex reaction media was obtained by acid value titration and by FTIR spectroscopic analyses using a conventional calibration method to measure the resinate concentration and the concentration of free rosin acids. A multivariate calibration method was successfully applied to make partial least square (PLS) models for monitoring acid value and solution viscosity in both mid-infrared (MIR) and near infrared (NIR) regions during the syntheses. The calibration models can be used for on line resinate process monitoring. In kinetic studies, two main reaction steps were observed during the syntheses. First a fast irreversible resination reaction occurs at 235 °C and then a slow thermal decarboxylation of rosin acids starts to take place at 265 °C. Rosin oil is formed during the decarboxylation reaction step causing significant mass loss as the rosin oil evaporates from the system while the viscosity increases to the target level. The mass balance of the syntheses was determined based on the resinate concentration increase during the decarboxylation reaction step. A mechanistic study of the decarboxylation reaction was based on the observation that resinate molecules are partly solvated by rosin acids during the syntheses. Different decarboxylation mechanisms were proposed for the free and solvating rosin acids. The deduced kinetic model supported the analytical data of the syntheses in a wide resinate concentration region, over a wide range of viscosity values and at different reaction temperatures. In addition, the application of the kinetic model to the modified resinate syntheses gave a good fit. A novel synthesis method with the addition of decarboxylated rosin (i.e. rosin oil) to the reaction mixture was introduced. The conversion of rosin acid to resinate was increased to the level necessary to obtain the target viscosity for the product at 235 °C. Due to a lower reaction temperature than in traditional fusion synthesis at 265 °C, thermal decarboxylation is avoided. As a consequence, the mass yield of the resinate syntheses can be increased from ca. 70% to almost 100% by recycling the added rosin oil.

Fotocromismo em filmes finos de óxidos de tungstênio de diferentes composições

Tungsten oxide thin films with three different compositions were deposited by reactive sputtering in an oxygen-argon plasma. In a system composed of a home made photochemical reactor coupled with an optic fiber spectrophotometer, the photochromic effect was studied in these oxide films as function of UV irradiation time, in ethanol, methanol and formaldehyde atmospheres. It was observed that the photochromic efficiency depends on the vapor chemical nature where the film is irradiated as well as the film composition. Kinetic analysis suggest that two kinds of optical absorption centers should respond by the photochromic effect in these films, one generated at film surface and other inside it, which one presenting a different time constant.

Fotocatálise eletroquímica de atrazina sobre dióxido de titânio: efeito de diferentes parâmetros experimentais

The atrazine photoelectrochemical degradation has been examined in solutions containing TiO2 on immobilized films under a variety of experimental conditions. It was possible to observe that the supporting electrolyte nature affects the intensity of the photocurrent, being an indicative of the adsorption process. The disappearance of the organic molecule follows approximately a pseudo-first order kinetic. As mineralization product, NH4+ and NO3- ion have been identified. These results indicated that the formation of NH4+ ion can be associated to the effect of atrazine adsorption, due to need of potential adaptation together with a variation in the supporting electrolyte concentration.

Technical Wind Energy Potential in Russia

The goal of the master's thesis is a detailed research of the technical wind energy potential in Russian Federation: the distribution of the potential all over the territory of the country and the possibility of the application of the potential for power supply of various objects. The main attention of the thesis is devoted to the assessment of wind energy resources (potential) of Russian Federation, both for the territory of country in whole and for every region. Theoretical basic wind energy concepts and the scheme of transformation of kinetic energy of a wind into electric energy by modern wind turbines are given in the work. Also the costs of energy, stimuli of development of wind-engineering and obstacles which impact the industry development are analyzed. The review of existent and projected wind power plants in Russia is carried out.

Um experimento de análise em fluxo envolvendo reações enzimáticas e quimiluminescência

An experiment is proposed to introduce some fundamentals of flow analysis, chemiluminescence and kinetic monitoring of enzymatic reactions in undergraduate courses. Chemiluminescence detection is performed with a simple spectrophotometer equipped with a lab-made spiral flow cell constructed from a polyethylene tube. The hydrogen peroxide produced by the glucose oxidation in the presence of glucose oxidase is continuously monitored by the reaction with luminol in alkaline media in a flow injection system. The exercise allows also the discussion of important analytical features and the comparison with different optical methods of analysis.

O eletrólito suporte e suas múltiplas funções em processos de eletrodo

The aim of this work is to present the principal properties and applications of supporting electrolytes (SE) to students, teachers and researchers interested in electrode processes. Different aspects are discussed including the importance of SE in maintaining constant the activity coefficients and the diffusion coefficients and reducing the transport number of electroactive species. Its effect on the electrochemical kinetic parameters is also presented.

Efecto de solvente sobre la descomposición térmica de trans-3,6-dimetil-3,6-difenil-1,2,4,5-tetraoxaciclohexano en solución

The thermal decomposition reaction of trans-3,6-dimethyl-3,6-diphenyl-1,2,4,5-tetraoxacyclohexane (acetophenone cyclic diperoxide, DPAF), in different solvents (methanol, 1,4-dioxane, acetonitrile and 2-propanol/benzene mixtures) in the initial concentration and temperature ranges of (4.2-10.5) x 10-3 M and 140.0 to 185.0 ºC, respectively, follows a pseudo first order kinetic law up to at least 70% DPAF conversion. An important solvent effect on the rate constant values, activation parameters (DH# and DS#) and reaction products obtained in different solvents is detected, showing that the reaction is accelerated in alcohols.

The trouble with resonance energies: a Hückel theory topic

Resonance energies are shown to be quasithermodynamic in character. Hence, they are generally unsuitable as bases for anticipating kinetic stabilities. Examples are provided, leading to the conclusion that those who intend the word 'aromatic' to mean chemically unreactive, need to carry out full Hückel calculations in order to rank hydrocarbons using the frontier orbital energies.