Chapter 17: Equilibrium and Equilibrium Constants

Enhanced Introductory College Chemistry

by Gregory Anderson; Caryn Fahey; Jackie MacDonald; Adrienne Richards; Samantha Sullivan Sauer; J.R. van Haarlem; and  David Wegman;

Chapter Contents

In this chapter, you will learn about

  • Chemical reaction rates
  • The dynamic nature of a chemical equilibrium
  • Equilibrium constants
  • The response of a stressed equilibrium using Le Châtelier’s Principle
  • Equilibrium calculations involving changes to the equilibrium
  • Equilibrium constants representing solubility, acids and bases
  • Real world examples of equilibria in nature

To better support your learning, you should be familiar with the following concepts before starting this chapter:

  • Chemical equations
  • Reaction stoichiometry
  • Molarity
  • Solubility
  • Reactions of acids and bases
The image depicts the movement of carbon dioxide from tissue into the blood vessel. C O subscript 2 moves from the cell to the bloodstream resulting in the equilibrium equation of C O subscript 2 plus H subscript 2 O connected by a double-headed arrow to H subscript 2 C O subscript 3 connected by a double-headed arrow to H C O subscript 3, super script negative sign plus H superscript positive sign.
Figure 17a: Movement of carbon dioxide through tissues and blood cells involves several equilibrium reactions (credit: Chemistry (OpenStax), CC BY 4.0).

Imagine a beach populated with sunbathers and swimmers. As those basking in the sun get too hot and want to cool off, they head into the surf to swim. As the swimmers tire, they head to the beach to rest. If these two rates of transfer (sunbathers entering the water, swimmers leaving the water) are equal, the number of sunbathers and swimmers would be constant, or at equilibrium, although the identities of the people are constantly changing from sunbather to swimmer and back. An analogous situation occurs in chemical reactions. Reactions can occur in both directions simultaneously (reactants to products and products to reactants) and eventually reach a state of balance.

These balanced two-way reactions occur all around and even in us. For example, they occur in our blood, where the reaction between carbon dioxide and water forms carbonic acid (HCO3) (Figure 17a). Human physiology is adapted to the amount of ionized products produced by this reaction (HCO3 and H+). In this chapter, you will learn how to predict the position of the balance and the yield of a product of a reaction under specific conditions, how to change a reaction’s conditions to increase or reduce yield, and how to evaluate an equilibrium system’s reaction to disturbances.

Attribution & References

Except where otherwise noted, this page is adapted by David Wegman from “Chapter 13 Introduction” In General Chemistry 1 & 2 by Rice University, a derivative of Chemistry (Open Stax) by Paul Flowers, Klaus Theopold, Richard Langley & William R. Robinson and is licensed under CC BY 4.0. ​Access for free at Chemistry (OpenStax)


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Enhanced Introductory College Chemistry Copyright © 2023 by Gregory Anderson; Caryn Fahey; Jackie MacDonald; Adrienne Richards; Samantha Sullivan Sauer; J.R. van Haarlem; and David Wegman is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

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