Chemical equilibrium

... A [ ,nxmIFl Q [prIl(,,,)t,.)] (29) QU =4rp,UpTcj (30) CA.C. UU 3 L1 200 JxxosnAw KosTRowicKi and ADAM Liwo should be done carefully, because bad initial guesses (31) may cause at the beginning too low values of the concentrations of the corresponding ... Spivey H. 0. Li E. LF. ...

The aim of this article was to study the reasons, strategies, and procedures that both students and teachers use to solve some chemical equilibrium questions and problems. Inappropriate conceptions on teaching and a lack of knowledge regarding the limited usefulness of Le Chatelier's principle, with its vague and ambiguous formulation and textbook presentation, may be some of the sources of misconceptions about the prediction of the effect of changing conditions on chemical equilibrium. To diagnose misconceptions and their possible sources, a written test was developed and administered to 170 1st-year university chemistry students. A chemical equilibrium problem, relating to the students' test, was solved by 40 chemistry teachers. First, we ascertained that teacher's conceptions might influence the problem-solving strategies of the learner. Based on this first aspect, our discussion also concerns students' and teachers' misconceptions related to the Le Chatelier's principle. Misconceptions emerged through: (a) misapplication and misunderstanding of Le Chatelier's principle; (b) use of rote-learning recall and algorithmic procedures; (c) incorrect control of the variables involved; (d) limited use of the chemical equilibrium law; (e) a lack of mastery of chemical equilibrium principles and difficulty in transferring such principles to new situations. To avoid chemical equilibrium misconceptions, a specific pattern of conceptual and methodological change may be considered.

Introdução ao equilíbrio químico;
Perturbações
- Perturbação no equilíbrio químico pela variação da concentração;
- Perturbação no equilíbrio químico pela variação da pressão e do volume do container;
- Perturbação no equilíbrio químico pela temperatura;
Relação entre equilíbrio químico e cinética química.
Constantes de equilíbrio em função da pressão ou concentração;
Cálculos e exercícios resolvidos

... in remaining char and increase in oxidant), thus the total amount of hydrogen in the product gas remains roughly constant. ... Bioenergy 84 Vol. 3 Biomass Conversion, 73-79. Durai-Swamy, K., DW Warren, B. Aghamahommadi, and MN Mansour. 1989. ...

In the field of chemistry there has been considerable interest in discovering the reasons why many students have great difficulty in successfully developing a scientifically accepted understanding of chemical equilibrium. Research projects influenced and inspired by constructivism have been invaluable for identifying alternative conceptions that may turn into obstacles to meaningful learning of fundamental ideas regarding chemical equilibrium. Research findings

The need for sustainable alternatives to oil has been of deep concern to many countries around the world, and especially the U.S. due to the rapidly rising cost of oil. As a result, many nations face significant energy security challenges stemming from their dependence on imported oil. To achieve future energy security and independence
and in the long run to prepare for the post-oil energy resources, biomass is considered as one of the most important renewable energy resources in a projected sustainable energy future. The key bottleneck for lignocellulosic-derived biofuels is the lack of technology for efficient conversion of biomass in to readily usable fuel products. Current
work provides a detailed theoretical and experimental analysis of two (air and steam only) gasification technologies which are carbon neutral that can be used to overcome this hurdle.

This work also examines the use of mixed ion-electron conductors (MIEC) membranes as a significant option to enhance the production of H2 from biomass feedstock. Currently there are technologies that produce H2 by using renewable energy sources other than biomass as feedstock but they could not provide a long term solution
because of their adverse effects on eco-system. Thin film SrCe0.7Zr0.2Eu0.1 O3-δ membranes were developed and supported using NiO-SrCe0.8 Zr0.2 O3-δ tubular structure, using Dr. Eric Wachsman’s group’s work at UF. The main advantage of this
membrane setup is that it acts as WGS reactor and also separates the H2 from the gas stream, thus avoiding the need for two stage reactor setup requiring WGS and H2 separation independently. The possibility of sequestering the isolated CO2 stream is also another attribute to such membrane reactors. The overall objective of this current work is to analyze the air gasification and steam only gasification technology in detail and to investigate the performance of proton conducting ceramic membranes at high temperatures. Current research also analyzed a
simplistic model of a concept system, which is a self-sustaining H2 fuel production system that integrates the gasification technology and the MIEC membrane technology. The proposed system enhances the H2 produced from the biomass feed stock by carrying out WGS.

The main objective of this study is to investigate the thermal profiles of a trailer-scale gasifier in different
zones during the course of gasification and also to elaborate on the design, characteristics and performance
of the gasification system using different biomass feedstock. The purpose is to emphasize on
the effectiveness of distributed power generation systems and demonstrate the feasibility of such gasification
systems in real world scenarios, where the lingo-cellulosic biomass resources are widely available
and distributed across the board. Experimental data on the thermal profiles with respect to five different
zones in the gasifier and a comprehensive thermal–chemical equilibrium model to predict the syngas
composition are presented in detail. Four different feedstock-pine wood, horse manure, red oak, and
cardboard were evaluated. The effects of C, H, O content variations in the feedstock on the thermal profiles,
and the efficiency and viability of the trailer-scale gasifier are also discussed.

We consider the onset of thermosolutal (double-diffusive) convection of a binary fluid in a horizontal porous layer subject to fixed temperatures and chemical equilibrium on the bounding surfaces, in the case when the solubility of the dissolved component depends on temperature. We use a linear stability analysis to investigate how the dissolution or precipitation of this component affects the onset

Biomass has great potential as a clean, renewable feedstock for producing modern energy carriers. This paper focuses on the process of biomass gasification, where the synthesis gas may subsequently be used for the production of electricity, fuels and chemicals. The gasifier is one of the least-efficient unit operations in the whole biomass-to-energy technology chain and an analysis of the efficiency of the gasifier alone can substantially contribute to the efficiency improvement of this chain. The purpose of this paper is to compare different types of biofuels for their gasification efficiency and benchmark this against gasification of coal. In order to quantify the real value of the gasification process exergy-based efficiencies, defined as the ratio of chemical and physical exergy of the synthesis gas to chemical exergy of a biofuel, are proposed in this paper. Biofuels considered include various types of wood, vegetable oil, sludge, and manure. In this study, exergetic efficiencies are evaluated for an idealized gasifier in which chemical equilibrium is reached, ashes are not considered and heat losses are neglected. The gasification efficiencies are evaluated at the carbon-boundary point, where exactly enough air is added to avoid carbon formation and achieve complete gasification. The cold-gas efficiency of biofuels was found to be comparable to that of coal. It is shown that the exergy efficiencies of biofuels are lower than the corresponding energetic efficiencies. For liquid biofuels, such as sludge and manure, gasification at the optimum point is not possible, and exergy efficiency can be improved by drying the biomass using the enthalpy of synthesis gas.

... Email: marissa.rollnick@wits.ac.za Page 2. ... The aim of the workshop was to provide these teachers with a variety of practical ideas for portraying the meaning of the mole, such as weighing a number of small everyday objects (eg, rice grains) in order to count them. ...

This paper examines the precipitation of Al (III) ion in water solutions of AlCl3 (10 mM,
5 mM and 3 mM) with phtalic acid and sulphosalicilic acid (100 mM, 10 mM and 1 mM)
in constant ionic strength of 0,6 M NaCl. The region of concentrations clearer solutions
were found and also where the solid phase is presented is determined. Solid phase is analyzed
by means of elementary chemical analysis, IR spectroscopy and x-ray diffraction.
The isolated compounds are:
Al(III) – phtalic acid Al8(OH)18 [C6H4(COO)2]3 ·5H2O
Al(III) – sulphosalicilic acid Al5(OH)13[C6H3OH(COO)SO3] ·2H2O
The product of solvability of isolated compounds can be approximately calculated in
the solid phases, which is of great importance to better understand the distribution of aluminum
in earth and in water.