Theory on the selection of A+ property methods – electrolyte model
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For a system with a solvent dielectric constant less than 10, ionic reactions do not take place. Therefore, the Aspen Physical Property System bypasses all solution chemistry calculations for such systems. If you define reactions on the Reactions Chemistry form, the Aspen Physical Property System checks for infeasible or redundant reactions. If such reactions exist, the Aspen Physical Property System ignores them during the calculations. This is the description of the ELECNRTL model in the A+ v7 help system: “For systems with a solvent dielectric constant less than 10, ionic reactions do not occur.” . . . ”, so what should the theoretical effect of the dielectric constant on ion reactions be like?
When only the effect of the dielectric constant ε of different solvents on the rate of ionic reactions is considered, there are some qualitative rules. The higher the dielectric constant of a solvent, the greater its polarity; according to the principle of \"like dissolves like,\" it exhibits stronger forces with molecules that are also highly polar. Therefore: (1) Solvents with a high ε are favorable for reactions that result in increased polarity. Due to the formation of an activated complex. For example, in the bromination of toluene, using CS2 (with a low ε) as solvent, benzyl bromide is the main product (85.2%) ； While using *** mainly yields o- and p-bromotoluene (98%). (2) Regarding the laws of ionic reactions: ① If the reactants are ions of the same charge, an increase in ε accelerates the reaction rate. This is because the repulsion between ions of the same sign decreases significantly with ε, making it easier to form a transition state. ②If the reactants are ions of opposite signs, an increase in ε leads to a decrease in the reaction rate. This is because the decrease in the attraction between ions of opposite signs due to ambassador ε is greater, making it more difficult to form activated complexes. ③If neutral molecules are present in the reactants, an increase in ε causes the reaction rate between ions and neutral molecules to decrease slightly. Due to the reduced polarity of the formed activated complex.