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The Groundwater Geochemical System
Published in William J. Deutsch, Groundwater Geochemistry, 2020
Each chemical reaction has associated with it an equilibrium constant (K). The equilibrium constant is a numerical value that represents the ratio of the activities (effective concentrations) of the participants in the chemical reaction when that reaction has reached chemical equilibrium. At equilibrium, the ratio of the activities will not change and can be represented as a constant (K). For example, calcite dissolution in water can be represented by the following reaction: () CaCO3(s)→Ca2++CO32−
Applications of Green Chemistry Principles in Engineering Introduction to Sustainability
Published in Vera M. Kolb, Green Organic Chemistry and Its Interdisciplinary Applications, 2017
Output-pulled design can also be achieved via temperature control of reversible reactions. One can consider exothermic and endothermic reactions in a way in which one imagines that heat itself behaves as a chemical reactant or product. Chemical equations that include heat are termed thermochemical (Brown and Holme, 2006). Such equations allow us to predict the response of a system with the change in temperature in the same way as we have done previously for the change in concentration. An important difference, however, is that the temperature change alters the value of the equilibrium constant. Table 8.3 shows the response of a system in equilibrium upon a change in temperature (Brown and Holme, 2006). A more rigorous treatment of the response of equilibrium to temperature can be found in Atkins and de Paola (2006).
Etherification
Published in Mark J. Kaiser, Arno de Klerk, James H. Gary, Glenn E. Hwerk, Petroleum Refining, 2019
Mark J. Kaiser, Arno de Klerk, James H. Gary, Glenn E. Hwerk
The temperature dependence of the equilibrium constant for the etherification reaction, Keq, is shown in Figure 34.3. The equilibrium constant decreases with increasing temperature. The equilibrium for etherification of olefins with methanol is also more favorable than etherification with ethanol. In the case of TAME, there are two equilibrium constants, because 2-methyl-1-butene and 2-methyl-2-butene are both reactive for etherification.
A numerical investigation of bio-convective electrically conducting water-based nanofluid flow on the porous plate with variable wall temperature
Published in Numerical Heat Transfer, Part A: Applications, 2023
Shuhe Sun, Shuguang Li, Sidra Shaheen, Muhammad Bilal Arain, Khalid Ali Khan
The least amount of energy needed for a particle to undergo various chemical alterations or reactions is called activation energy, or Ea. Mechanochemistry, food processing, chemical engineering, geothermal, and oil storage all use activation energy. The impression of activation energy upon the outlines of concentration is portrayed in Figure 8. The amount of nanofluid within the boundary layer augments as the activation energy rises. As a result, energy flow encounters more resistance. Figure 9 shows how the chemical reaction constant affects concentration boundary layer thickness. The proportionality constant, known as the rate constant, links the rate of a chemical reaction to the concentrations of reacting components in an equation. Looking at the equilibrium constant allows us to determine whether a response tends to have a higher concentration of products or reactants at equilibrium. The concentration boundary layer’s thickness is observed to decrease as chemical reaction constant rises.
Catalysts used in biodiesel production: a review
Published in Biofuels, 2021
A catalyst is a substance that increases the chemical reaction rate without being consumed by the reaction itself. Theoretically, the catalyst is practically consumed in one stage and regenerated at a later stage, and this operation is continuously repeated without imposing a permanent change on the catalyst. Accordingly, the catalyst in a given reaction can be recycled unchanged at the end of the reaction. Catalysts change the speed of a chemical reaction that can be thermodynamically carried out. Therefore, they cannot perform reactions that are not thermodynamically feasible. Basically, a catalyst is considered a chemical compound capable of applying an accelerating effect on the reaction rate and a directional effect on the reaction progression which is thermodynamic in nature. In a reversible reaction, the catalyst evenly affects the rate of forward and backward reactions. Therefore, the equilibrium constant of the reaction is the same whether in the presence of a catalyst or without it. When there are several mechanisms available for the reaction, the catalyst must be selected. In principle, the catalyst should increase the ratio of the desired material to the unwanted material. Although ideally catalysts remain unchanged during the reaction, this is inaccurate in practice, since the catalyst itself is a reactive substance that undergoes irreversible physical and chemical changes during the reaction, reducing its ability to function. Over time, this reality may be vividly observed since the catalyst enters into billions of reactions [5]. In general, the catalysts used in the transesterification of vegetable oils and animal fats can be classified into three groups – homogeneous, heterogeneous and enzymatic catalysts [12] – as shown in Figure 1.
Revisiting the Kellogg diagrams: roaster diagrams and their usefulness in pyrometallurgy
Published in Mineral Processing and Extractive Metallurgy Review, 2018
M. Sadegh Safarzadeh, Stanley M. Howard
The values of equilibrium constants are fixed when the temperature is fixed. Regardless of the metal used in the M–S–O system, the slope of each line in the diagram remains the same being a consequence of stoichiometry only. The equilibrium constant for each metal system determines the intercept, thus position of each line. As an example, the predominance area diagram for the Zn–S–O system at 900 K is shown in Figure 2. The equilibrium constants at 900 K were calculated using the data shown in Table 1. Also, shown in Figure 2 is the loci where the total pressure of all gases equals 0.2 atm.