Author: admin
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Thermodynamic Network for Electrolyte Equilibria
Equilibrium Constants Suppose an electrolyte has a chemical formula C2A where C+ is a monovalent cation and A2– is a bivalent anion. Succinic acid, H2Succ, is an example of an electrolyte with this formula. An equilibrium network can be created as shown in Fig. 18.2. An electrolyte with an arbitrary C2A composition is shown, with the expectation that…
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The Definition of pH
The pH of a solution is defined to be where the activity is expressed on the molal scale. Methods for calculating the activity are covered later. Commonly as an approximation, the concentration (mol/L) is substituted, and the “p” notation stands for the negative of the common logarithm: We use this common approximation for introductory examples.…
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Concentration Scales and Standard States
To discuss the concentration of an electrolyte, some terminology conventions are important for clarity. For example, when 0.01 mole of sodium chloride is added to water and diluted to 1 liter at 25°C, the solution results in 0.02 mol/L of ions because it acts as a strong electrolyte. However, we need a method to communicate…
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Speciation and the Dissociation Constant
The term speciation refers to a cataloging of the species that exist in solution. The species are characterized by writing dissociation reactions that identify the species and material balance constraints that exist in solution. To introduce the concepts of speciation, consider the dissociation of water: Thus, in pure water, the species in solution are H2O, H+, and…
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Colligative Properties
Boiling points, freezing points and osmotic pressure are sometimes termed colligative properties. The adjective “colligative” describes phenomena that are dependent on molar concentration and ignore the solution nonidealities. This of course is an approximation. We understand from previous chapters discussing nonelectrolytes that solution nonidealities can be important. However, in the case of dissolved solids such as sodium…
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Introduction to Electrolyte Solutions
Briefly, an electrolyte is a substance that dissociates into charged species in a liquid phase. The behavior can occur in solution, or in the case of ionic liquids used as nonvolatile solvents, occurs in the pure state. Electrolytes exist in biological and industrial systems and are thus important to our everyday life. Sodium chloride almost totally…
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Homework Problems
17.1. For their homework assignment three students, Julie, John, and Jacob, were working on the formation of ammonia. The feed is a stoichiometric ratio of nitrogen and hydrogen at a particular T and P. Julie, who thought in round numbers of product, wrote: John, who thought in round numbers of nitrogen, wrote: N2 + 3H2 2NH3 Jacob, who thought in round…
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Practice Problems
P17.1. An equimolar mixture of H2 and CO is obtained by the reaction of steam with coal. The product mixture is known as “water-gas.” To enhance the H2 content, steam is mixed with water-gas and passed over a catalyst at 550°C and 1 bar so as to convert CO to CO2 by the reaction: Any unreacted H2O is subsequently…
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Summary
We have greatly enlarged the scope of our coverage of engineering thermodynamics with very little extension of the conceptual machinery. All we really did conceptually was recall that the Gibbs energy should be minimized. The provision that atoms can be moved from one chemical species to another with commensurate changes in energy and entropy simply…
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Simultaneous Reaction and VLE
It is not difficult to imagine situations in which reactions take place in the presence of multiple phases. Absorption of CO2 into NaOH solution involves a reaction of the CO2 as it dissolves to form sodium bicarbonate and sodium carbonate. Hydrogen bonding in “pure” fluids implies reaction and phase equilibrium at saturation conditions. The production of methyl…