Endothermic process equilibrium constant

In Figure 2.4, data for the equilibrium constants of esterification/hydrolysis and transesterification/glycolysis from different publications [21-24] are compared. In addition, the equilibrium constant data for the reaction TPA + 2EG BHET + 2W, as calculated by a Gibbs reactor model included in the commercial process simulator Chemcad, are also shown. The equilibrium constants for the respective reactions show the same tendency, although the correspondence is not as good as required for a reliable rigorous modelling of the esterification process. The thermodynamic data, as well as the dependency of the equilibrium constants on temperature, indicate that the esterification reactions of the model compounds are moderately endothermic. The transesterification process is a moderately exothermic reaction. 

Le Chatelier s principle predicts that when heat is added at constant pressure to a system at equilibrium, the reaction will shift in the direction that absorbs heat until a new equilibrium is established. For an endothermic process, the reaction will shift to the right towards product formation. For an exothermic process, the reaction will shift to the left towards reactant formation. If you understand the application of Le Chatelier s principle to concentration changes then writing "heat" on the appropriate side of the equation will help you understand its application to changes in temperature. 

The endothermic nature of this exchange process on smectites has been verified from the effect of temperature on the equilibrium constant of exchange, Ke. The van t Hoff equation ... 

The agreement between the values of kinetic parameters and the thermodynamics of the process. On the one hand, the activation energy for an elementary endothermic reaction cannot be less than the heat of reaction. On the other hand, if the data about rate constants for both direct and reverse reactions are available, their ratio should be equal to the equilibrium constant calculated independently from thermodynamic data for species participating in the reaction. 

For endothermic reversible reactions there is no direct process optimization problem with regard to the temperature. For endothermic reversible reactions higher temperatures are always favourable for both the rate of reaction and the equilibrium conversion. The dependence of the equilibrium constant upon temperature for reversible reactions is usually given by ... 

Le Chatelier s principle predicts that when heat is added at constant pressure to a system at equilibrium, the reaction will shift in the direction that absorbs heat until a new equilibrium is established. For an endothermic process, the reaction will shift to the right towards product formation. 

Dissociation of reactant A is an endothermic process in which the entropy change is positive. Consequently, the equilibrium constant increases at higher temperature via Le Chatelier s principle, which shifts the reaction to the right in favor of... 

In the case of exothermic reactions (negative values of the standard enthalpy of reaction), the equilibrium constant will decrease with increasing temperature. This means that also the maximum conversion will decrease, as for example, in the case of the SO3 and the NH3 production. The opposite is true in the case of endothermic reactions, for example, in the case of the production of synthesis gas (CO and H2) by the steam reforming process. Qualitatively, this behavior is shown in Figure 12.4. While for endothermic reactions, high temperatures have to be realized (see Examples 12.6 and 12.8) to get high conversions. For exothermic reactions low temperatures are needed, although it must be taken into account that at low temperatures the reaction rates are slow. 

That is, the autoionization of water is an endothermic process. According to Le Chatelier s principle (Section 10.4), the equilibrium of an endothermic process will shift in the direction of products when the temperature is increased, leading to a corresponding increase in the equilibrium constant. Therefore, the value of K will be larger than its value at 25°C (1.01 X 10" " ) for temperatures above 25°C and smaller than its value at 25°C for temperatures below 25°C. Table 11.2 shows the value of at a variety of temperatures. 

Nickel that is more than 99.9% pure can be produced by the carbonyl process Impure nickel combines with CO at 50 C to produce Ni(CO)4( ). The Ni(CO)4 is then heated to 200°C, causing it to decompose back into Ni(s) and CO g). (a) Write the equilibrium-constant expression for the formation of Ni(CO)4 (b) Given the temperatures used for the steps in the carbonyl process, do you think this reaction is endothermic or exothermic (c) In the early days of automobiles, nickel-plated exhaust pipes were used. Even though the equilibrium constant for the formation of Ni(CO)4 is very small at the temperature of automotive exhaust gases, the exhaust pipes quickly corroded. Explain why this occurred. 

Reforming of natural gas is a common process for the production of hydrogen, where the yield is a function of the equilibrium established among the different chemical species and depends on the operating pressure, due to the difference in the number of moles in the stoichiometry, and on the temperature, as the reforming reaction is endothermic. The stoichiometry and the equilibrium constants are given by Equations ll.10andll.il [11] ... 

For an exothermic reaction, the difference in enthalpy between products and starting materials is negative and the equilibrium constant (K) is greater than 1. For an endothermic reaction (read the first reaction backward to produce an endothermic process), the enthalpy difference is positive and K is less than 1. 

An equilibrium constant of 5.4 translates into 84.4% product at equilibrium One would very often be quite happy to find a reaction that gives about 85% product, and a mere 1 kcal/mol suffices to ensure this. Conversely, if we are fighting a 1-kcal/mol endothermic process, it will be a futile fight indeed because equilibrium will settle out at 84.4% starting material. A little bit of energy goes a long way at equilibrium. Table 8.1 summarizes a number of similar calculations. 

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