12: Equilibrium Chemistry
- Page ID
- 526616
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Regardless of the problem on which an analytical chemist is working, its solution requires a knowledge of chemistry and the ability to apply that knowledge to solve a problem. For example, an analytical chemist who is studying the effect of pollution on spruce trees needs to know, or know where to find, the chemical differences between p‐hydroxybenzoic acid and p‐hydroxyacetophenone, two common phenols found in the needles of spruce trees.
The ability to “think as a chemist” is a product of your experience in the classroom and in the laboratory. For the most part, the material in this text assumes you are familiar with topics covered in earlier courses; however, because of its importance to analytical chemistry, this chapter provides a review of equilibrium chemistry. Much of the material in this chapter should be familiar to you, although some topics—ladder diagrams and activity, for example—likely afford you with new ways to look at equilibrium chemistry.
- 12.1: Reversible Reactions and Chemical Equilibria
- In 1798, chemist Claude Berthollet observed Na2CO3 deposits at Egypt's Natron Lakes, which contradicted existing chemical theory based on elective affinities that dictated reactions proceed in one direction only. Berthollet's insight into the reversibility of reactions, exemplified by the formation of Na2CO3 using CaCO3 and NaCl, contributed to the understanding of chemical equilibrium.
- 12.2: Thermodynamics and Equilibrium Chemistry
- The page discusses the principles of thermodynamics, focusing on chemical reactions and the factors influencing their equilibrium positions. It outlines the roles of Gibbs free energy, enthalpy, and entropy in determining whether reactions are thermodynamically favorable. The Gibbs free energy equation predicts reaction direction under specific conditions. The equilibrium constant (K) describes a reaction's equilibrium position using concentrations or partial pressures.
- 12.3: Manipulating Equilibrium Constants
- The page elaborates on two principles regarding equilibrium constants: reversing a reaction inverts its equilibrium constant, and combining reactions involves multiplying their equilibrium constants. An example and exercise demonstrate these principles. For the example, the equilibrium constant for a reaction is calculated by combining constants of related reactions, resulting in 0.10. In a similar exercise, the equilibrium constant for a different reaction is calculated to be approximately 31.
- 12.4: Equilibrium Constants for Chemical Reactions
- The document provides an in-depth overview of several essential chemical reactions relevant to analytical chemistry, such as precipitation, acid-base, complexation, and oxidation-reduction (redox) reactions. It explains the concepts of equilibrium constants like Ksp for precipitation reactions, Ka and Kb for acid-base reactions, and Kf for complexation reactions. The text discusses strong and weak acids and bases, amphiprotic species, the dissociation of water, and the pH scale.
- 12.5: Ladder Diagrams
- The page discusses the importance of considering chemical interactions, like pH and solubility, when developing or evaluating analytical methods. It critiques the inappropriate use of NH3 in precipitating AgCl due to its solubility-increasing effect. Key analytical errors often stem from overlooking chemical interferences. Ladder diagrams are introduced as tools for visualizing equilibrium chemistry, aiding in understanding reaction dynamics and evaluating changes in solution conditions.
- 12.6: Problems
- This page contains a comprehensive set of chemistry problems related to equilibrium constants, redox reactions, solubility, acid-base equilibrium, buffer solutions, and complexation reactions. It starts with deriving equilibrium constant expressions for given chemical reactions, analyzing the favorability of reactions using ladder diagrams, and calculating potentials for redox systems.
- 12.7: Additional Resources
- The page provides a comprehensive list of references addressing various aspects of equilibrium chemistry. Topics covered include experimental determination of equilibrium constants, the impact of ionic strength, solubility products, and buffer capacity. Historical perspectives on the field are also offered. Additionally, the list encompasses instructional strategies, simulations for teaching, and critiques of conventional approaches to equilibrium concepts.
- 12.8: Chapter Summary and Key Terms
- The chapter discusses analytical chemistry as the application of chemistry to analyze samples, focusing on using chemical reactivity to dissolve samples, separate analytes, transform analytes, or provide a signal. Key reactions include precipitation, acid-base, metal-ligand complexation, and oxidation-reduction. It also covers equilibrium concepts, such as Le Ch??telier's principle, and solutions like buffers, using equilibrium constants, ladder diagrams, and activity coefficients.