Modelling the adsorption of phospholipid vesicles to a silicon dioxide surface using Langmuir kinetics

The rate constants and equilibrium constant for the adsorption and desorption of lipid vesicles from a SiO2 surface have been determined.

The study of phosphate ions sorption from silicon dioxide solutions obtained by using acid decomposition of nepheline

The process of sorption of phosphate ion by silicon dioxide obtained by acid decomposition of nepheline is studied. The experimental data were processed using the Freundlich and Langmuir sorption equations, which showed that the sorption process is fairly accurately described by both equations, while the use of the Langmuir monomolecular adsorption equation is preferable in the calculations. The capacity of the adsorption monolayer of the synthesized sample relative to the РО43–-ion and the adsorption equilibrium constant are calculated. Based on the obtained data, various options for sorption treatment of municipal wastewater from РО43--ion to normalized MPC values were evaluated.

Binding Reactions at Finite Systems

A perpetual yearn exists among computational scientists to scale-down the size of physical systems, a desire shared as well with experimentalists able to track single molecules. A question then arises whether averages observed at small systems are the same as those observed at large, or macroscopic, systems. Utilizing statistical-mechanics formulations in ensembles in which the total numbers of particles are fixed, we demonstrate that system's properties of binding reactions are not homogeneous functions. That means averages of intensive properties, such as the concentration of the bound-state, at finite-systems are different than those at large-systems. The discrepancy increases with decreasing numbers of particles, temperature, and volume. As perplexing as it may sound, despite these variations in average quantities, extracting the equilibrium constant from systems of different sizes does yield the same value. The reason is that correlations in reactants' concentrations are ought be accounted for in the expression of the equilibrium constant, being negligible at large-scale but significant at small-scale. Similar arguments pertain to the calculations of the reaction rate-constants, more specifically, the bimolecular rate of the forward reaction is related to the average of the product (and not to the product of the averages) of the reactants' concentrations. Furthermore, we derive relations aiming to predict the composition of the system only from the value of the equilibrium constant. All predictions are validated by Monte-Carlo and molecular dynamics simulations. An important significance of these findings is that the expression of the equilibrium constant at finite systems is not dictated solely by the chemical equation but requires knowledge of the elementary processes involved.

Formation of carnosine - an ab initio study

Formation of carnosine from histidine and b-alanine is studied by ab initio MO-LCAO-SCF method followed by the perturbative configuration interaction (MP2) in vacuo. After the full geometry optimization at the SCF level, the molecular properties were evaluated and followed by the vibrational-rotational analysis. Consequently, the energy, entropy and free energy were evaluated for the reactants and products of the reaction histidine + beta-alanine = carnosine + H2O and finally the equilibrium constant was enumerated.

Conceptions and troublesome knowledge on acid-base using the two-tier multiple-choice diagnostic test

Acid-base is one of the materials that tend to be difficult for students to understand. Acid-base is a material that is conceptually solid and requires an integrated understanding of many of the concepts of introductory chemistry. This research is descriptive research that aims to find conceptions of students on acid-base subjects and asking about concepts that are considered troublesome according to their learning experiences. The subjects of this research were 31 students of class XI IPA 4 at SMAN 3 Pariaman. The instruments in this research are diagnostic tests and interviews. The result of this research is the students of SMAN 3 Pariaman have difficulties in learning about the acid-base subject with high category. The percentage of conceptions experienced by students in each indicator is 56.3% of students understand the concept, 20.8% misconception, and 22.9% do not understand the concept. In the second indicator, 45.2% of students understood the concept, 18.3% had misconceptions and 36.5% did not understand the concept. In the 3rd indicator, 35.5% of students understood the concept, 31.2% had misconceptions and 33.3% did not understand the concept. In the 4th indicator, 21.9% of students understand the concept, 27.7% do not understand the concept and 50.3% do not understand the concept. Meanwhile, the acid-base theory, the calculation of pH or pOH, and the relationship between the degree of acidity (pH) and the degree of ionization (a), and the acid equilibrium constant (Ka) or the base equilibrium constant (Kb) are considered troublesome knowledge because they can be conceptually difficult.

Theoretical evaluation of equilibrium constant for boron isotopes exchange between boric acid and borate in pure and saline water

Evaluation of the equilibrium constant of boron isotope fractionation between boric acid and borate (k3−4) in water is of high geochemical importance, due to its contribution in reconstruction of ancient seawater pH and atmospheric CO2. As a result, precise evaluation of k3−4 has been the subject of numerous studies, yielding diverse and controversial results. In the present study, employing three different rigorous and high-precision theoretical approaches, we provide a reliable estimation of k3−4 which is a value between 1.028 to 1.030 for both pure and saline water. Within the context of present study, we also propose partial normal mode analysis, Boltzmann weighted averaging and a revision on the Bigeleisen and Mayer method which allow a more rigorous evaluation of isotope fraction in solution and can be used for studying other isotopic systems as well.

Fundamentals of Electrochemistry

Fundamentals of Electrochemistry build on basic oxidation-reduction reactions and present an overview of their use in electrochemical cells. The construction and operation of a galvanic cell is described with cell diagrams including the function of the electrodes (cathode and anode). Also covered are the standard electrode potential and its applications, including calculations involving the standard electrode potential, the Gibbs free energy and the equilibrium constant, determination of the spontaneity in redox reactions and the dependence of cell potential on concentration (the Nernst equation). Finally a qualitative and quantitative overview of electrolysis is presented with a focus on predicting the products of electrolysis and the stoichiometry of electrolysis, which relates the charge flowing through an electrolytic cell to the amount of products formed at the electrodes.

Chemical Thermodynamics

Chemical Thermodynamics discusses the fundamental laws of thermodynamics along with their relationships to heat, work, enthalpy, entropy, and temperature. Predicting the direction of a spontaneous change and calculating the change in entropy of a reaction are core concepts. The relationship between entropy, free energy and work is covered. The Gibbs free energy is used quantitatively to predict if reactions or processes are going to be exothermic and spontaneous or endothermic under the stated conditions. Also explored are the enthalpy and entropy changes during a phase change. Finally the Gibbs free energy of a chemical reaction is related to its equilibrium constant and the temperature.

Chemical Equilibrium

Chemical Equilibrium reviews the principles of equilibrium in systems of gases and liquids, starting with the concepts of reversible and irreversible reactions and dynamic equilibrium. The equilibrium constant (K) and reaction quotient (Q) are described, and comparison of K and Q is used to determine the direction in which a reaction must proceed to reach equilibrium. Calculations involving K in terms of concentration and pressure are presented. The relationship between the magnitude of K, the equilibrium position and the concentrations of reactants and products is discussed for both homogeneous and heterogeneous equilibria. The chapter ends with a qualitative treatment of equilibrium based on Le Chatelier’s principle, as well as how changes in reaction conditions can disturb a chemical equilibrium and how the chemical reaction responds to those changes.