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Chemical Equilibria: Systematic Approach to Equilibrium Calculations

Chemical Equilibria: Systematic Approach to Equilibrium Calculations

Equilibrium calculations for systems involving multiple equilibria are often complex. For example, to calculate the solubility of a sparingly soluble salt in an aqueous solution in the presence of a common ion, one must consider all the equilibria in this solution. Calculations for these systems can be complicated and tedious, so a systematic approach with a series of steps is often helpful. The process is detailed below.
The first step is to identify all the chemical reactions involved, The...

The Phase Rule

The Phase Rule

The phase rule describes the relationship between the variance (degrees of freedom), the number of components, and the number of phases in a system at equilibrium.Variance is a concept that denotes the number of independent intensive properties (properties are those that do not depend on the amount of material in the system), such as temperature, pressure, and composition, that can be altered without impacting the number of phases in equilibrium.In a single-component system, such as pure water,...

Homogeneous Equilibria for Gaseous Reactions

Homogeneous Equilibria for Gaseous Reactions

Homogeneous Equilibria for Gaseous Reactions
For gas-phase reactions, the equilibrium constant may be expressed in terms of either the molar concentrations (Kc) or partial pressures (Kp) of the reactants and products. A relation between these two K values may be simply derived from the ideal gas equation and the definition of molarity. According to the ideal gas equation:

Calculating the Equilibrium Constant

Calculating the Equilibrium Constant

The equilibrium constant for a reaction is calculated from the equilibrium concentrations (or pressures) of its reactants and products. If these concentrations are known, the calculation simply involves their substitution into the Kc expression.
For example, gaseous nitrogen dioxide forms dinitrogen tetroxide according to this equation:

The Equilibrium Constant

The Equilibrium Constant

Consider the oxidation of sulfur dioxide:

Calculating Equilibrium Concentrations

Calculating Equilibrium Concentrations

Being able to calculate equilibrium concentrations is essential to many areas of science and technology—for example, in the formulation and dosing of pharmaceutical products. After a drug is ingested or injected, it is typically involved in several chemical equilibria that affect its ultimate concentration in the body system of interest. Knowledge of the quantitative aspects of these equilibria is required to compute a dosage amount that will solicit the desired therapeutic effect.
A more...

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Phase Behavior of Charged Vesicles Under Symmetric and Asymmetric Solution Conditions Monitored with Fluorescence Microscopy

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Group Contribution Methods for Phase Equilibrium Calculations.

Jürgen Gmehling¹, Dana Constantinescu, Bastian Schmid

¹Department of Industrial Chemistry, University of Oldenburg, D-26111 Oldenburg, Germany;

Annual Review of Chemical and Biomolecular Engineering

|August 7, 2015

Summary

Predictive thermodynamic models, like group contribution methods, are crucial for chemical process simulation when experimental data is scarce. These models, utilizing group interaction parameters and databases like Dortmund Data Bank, enable accurate phase equilibrium calculations.

Keywords:

electrolyte model equation of state gE–model process design process development solvent selection

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Area of Science:

Chemical Engineering
Thermodynamics
Process Simulation

Background:

Chemical process development relies on accurate property data for simulation.
Separation processes are vital, necessitating reliable phase equilibrium data.
Existing models often lack sufficient experimental data for parameter fitting.

Purpose of the Study:

To review group contribution methods for predicting phase equilibrium data.
To assess the status, strengths, and weaknesses of these predictive models.
To highlight their application in chemical process design.

Main Methods:

Utilizing group contribution methods for phase equilibrium prediction.
Leveraging comprehensive databases (e.g., Dortmund Data Bank) for group interaction parameters.
Analyzing existing literature on predictive thermodynamic models.

Main Results:

Group contribution methods offer a viable solution for data-scarce scenarios.
These methods require fitting group interaction parameters using available experimental data.
Databases are essential for the development and application of these methods.

Conclusions:

Predictive thermodynamic models, particularly group contribution methods, are indispensable for modern chemical process simulation.
The availability of comprehensive databases significantly enhances the accuracy and applicability of these models.
Further development and validation of group contribution methods are crucial for advancing chemical engineering.