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9: Chemical Equilibria

Last updated

Apr 13, 2022
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- 8.S: Phase Equilibrium (Summary)
- 9.1: Prelude to Chemical Equilibria

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As was discussed in Chapter 6, the natural tendency of chemical systems is to seek a state of minimum Gibbs function. Once the minimum is achieved, movement in any chemical direction will not be spontaneous. It is at this point that the system achieves a state of equilibrium.

9.1: Prelude to Chemical Equilibria
The passage discusses the behavior of chemical systems, which naturally seek to achieve a state of minimum Gibbs function. When this minimum is reached, the system is in a state of equilibrium, and spontaneous chemical movement ceases. The direction of spontaneous change is related to the minimization of the partial derivative of Gibbs function with respect to the extent of reaction (??). A negative slope indicates a shift toward products, while a positive slope favors reactants.
9.2: Chemical Potential
The page explains the concept of chemical equilibrium, focusing on how the chemical potential of reactants and products balance. Using the reaction A(g) ??? B(g), equilibrium is reached when chemical potentials equate. For ideal gases, this involves using mole fractions and equilibrium constants (K???). It discusses calculating the Gibbs free energy changes and their relation to K???, highlighting that ??G < 0 indicates a spontaneous reaction.
9.3: Activities and Fugacities
The text discusses the concept of thermodynamic equilibrium constants, emphasizing that they are unitless and expressed in terms of activities and fugacities rather than concentrations or pressures. Activities of solids and pure liquids are considered unity, assuming ideal behavior, and don't affect the equilibrium constant's magnitude.
9.4: Pressure Dependence of Kp - Le Châtelier's Principle
The page discusses the effect of pressure on chemical equilibria, focusing on Le Chatelier's principle which states that a system will adjust to reduce stress when disturbed. While the equilibrium constant K??? remains unchanged with pressure at a fixed temperature, pressure changes impact equilibrium mixtures' composition.
9.5: Degree of Dissociation
Reactions such as the one in the previous example involve the dissociation of a molecule. Such reactions can be easily described in terms of the fraction of reactant molecules that actually dissociate to achieve equilibrium in a sample. This fraction is called the degree of dissociation.
9.6: Temperature Dependence of Equilibrium Constants - the van ’t Hoff Equation
The page discusses the temperature dependence of the equilibrium constant using the van 't Hoff equation. It explains how the equilibrium constant is temperature-dependent due to changes in standard Gibbs energy, with temperature, unlike its pressure independence.
9.7: The Dumas Bulb Method for Measuring Decomposition Equilibrium
The Dumas Bulb experiment is a method to study the temperature-dependent dissociation of N2O4 gas, commonly used in physical chemistry labs. The experiment measures the dissociation degree by equilibrium gas density at varying temperatures in a calibrated glass bulb. A formula calculates dissociation, factoring in measured versus theoretical densities, and an equilibrium constant is derived. The data enables the construction of a van't Hoff plot, providing insights into reaction enthalpy.
9.8: Acid-Base Equilibria
This page explains the principles of acid-base reactions and proton transfer processes, emphasizing the importance of pH in biological systems. It covers the dissociation of weak acids using acetic acid as an example, demonstrating the calculation of pH using equilibrium constants. The auto-ionization of water is discussed, illustrating how water dissociates into ions and explaining pH variations with temperature.
9.9: Buffers
Buffer solutions are essential for pH control in various processes and involve the equilibrium between a weak acid and its conjugate base. The pH of a buffer can be calculated using an ICE table or the Henderson-Hasselbalch approximation. The accuracy of these calculations relies on the pK??? and concentrations being sufficiently large to maintain equilibrium conditions close to their initial values.
9.10: Solubility of Ionic Compounds
This page discusses the solubility of ionic compounds in water using equilibrium concepts. The solubility product, $K_{sp}$ , is the equilibrium constant describing the solubility of an electrolyte. Two examples illustrate the calculations for solubility.
9.E: Chemical Equilibria (Exercises)
Exercises for Chapter 9 "Chemical Equilibria" in Fleming's Physical Chemistry Textmap.
9.S: Chemical Equilibria (Summary)
The page lists various vocabulary terms and concepts related to chemistry, such as common ion effect, conjugate base, degree of dissociation, and others. It also includes references to scientific literature and textbooks where these concepts may be explored in more detail. No further context or summary is provided regarding the terms themselves.

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