Author: admin
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Ideal Chemical Theory for Binary Systems
The simplest method of modeling complex behavior is to neglect the nonidealities by modeling a vapor phase as an ideal gas mixture including the complexes (true fugacity coefficients equal to 1), and to model a liquid phase as an ideal solution containing complexes (true activity coefficients equal to 1). This approach is called Ideal Chemical…
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Balance Equations for Binary Systems
The balance equations to be solved take the same form for both vapors and liquids. The liquid equations will be shown, and the reader should recognize the vapor equations by analogy. First, the true mole fractions must sum to unity: In a binary system, a balance equation can be written for either component to match…
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Equilibrium Criteria
Mole Balance One may wonder how quantification of the phenomena can be approached in a generalized fashion, but the criteria are presented clearly by Prigogine and Defay (1954) whose proof we reproduce here with modified notation. The first balances that must be satisfied are the material balances. For a binary solution created from nA moles of A, and nB moles…
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Introducing the Chemical Contribution
Evidence of complexation is often subtle and could be overlooked or ignored in many situations, but its effects are irrefutable in other situations, so a question arises about ignoring facts because they are inconvenient. For example, dimerization of carboxylic acids is observable in the saturated vapor compressibility factor of small acids, but less so for…
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Practice Problems
P18.1. a. Compute the freezing point depression for an aqueous solutions that is 3 wt% NaCl. b. Compute the boiling point elevation for an aqueous solutions that is 3 wt% NaCl. c. Compute the osmotic pressure for an aqueous solutions that is 3 wt% NaCl. 18.27. Homework Problems 18.1. Calcium chloride is used occasionally as an alternative to sodium…
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Supplement 4: Conversion of Equilibrium Constants
Equilibrium constants in electrolyte literature are often presented on the molal scale. For clarity in this section, we will use Ka,m to denote the molality equilibrium constant and Ka to denote the rational (Henry’s law scale) using mole fractions. Recall that the solvent (usually water) is on the Lewis-Randall scale. Using the molality scale for the electrolytes, On the…
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Supplement 3: Standard States
An important principle of the following discussion is that the chemical potential should be a property of the state of the system. All models should result in an identical value for the chemical potential at the same state. The standard state provides a convenient reference condition, but is slightly different from a reference state because…
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Supplement 2: Relation of Apparent Chemical Potential to Species Potentials
To understand the origin of the models for the mean activity coefficient, some discussion of the chemical potentials is necessary. Many of the concepts are extensions of the methods used for reaction engineering. For example, consider the general case of an electrolyte dissociating in solvent. When an electrolyte dissociates, the material balance gives the molality…
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Supplement 1: Interconversion of Concentration Scales
Throughout this chapter, subscript s indicates solvent, and Mw,i represents molecular wt in (g/mol). relation of mole fraction to molality: The relation for molality leads to another commonly used substitution for xs,
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Summary
This chapter began with a review of acid-base behavior to stress the importance of pH on equilibrium. Compounds are in the acid form below the pKa,A and in the base form above. Techniques including Sillèn’s graphical method were provided to determine solution pH values and species distributions at various concentrations. We explained the origin of charges…