So far in this text, when we present a chemical reaction, we have implicitly assumed that the reaction goes to completion. Indeed, our stoichiometric calculations were based on this; when we asked how much of a product is produced when so much of a reactant reacts, we are assuming that all of a reactant reacts. However, this is usually not the case; many reactions do not go to completion, and many chemists have to deal with that. In this chapter, we will study this phenomenon and see ways in which we can affect the extent of chemical reactions.
- 13.1: Prelude to Chemical Equilibrium
- More chemical reactions come to an equilibrium. The actual position of the equilibrium-whether it favors the reactants or the products-is characteristic of a chemical reaction; it is difficult to see just by looking at the balanced chemical equation. But chemistry has tools to help you understand the equilibrium of chemical reactions-the focus of our study in this chapter.
- 13.2: Chemical Equilibrium
- Chemical reactions eventually reach equilibrium, a point at which forward and reverse reactions balance each other's progress. Chemical equilibria are dynamic: the chemical reactions are always occurring; they just cancel each other's progress.
- 13.3: The Equilibrium Constant
- Every chemical equilibrium can be characterized by an equilibrium constant, known as Keq. The Keq and KP expressions are formulated as amounts of products divided by amounts of reactants; each amount (either a concentration or a pressure) is raised to the power of its coefficient in the balanced chemical equation. Solids and liquids do not appear in the expression for the equilibrium constant.
- 13.4: Shifting Equilibria - Le Chatelier's Principle
- Le Chatelier's principle addresses how an equilibrium shifts when the conditions of an equilibrium are changed. The direction of shift can be predicted for changes in concentrations, temperature, or pressure. Catalysts do not affect the position of an equilibrium; they help reactions achieve equilibrium faster.