13: Chemical Equilibrium
- Page ID
- 409112
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So far in this text, when presented a chemical reaction, it has been implicitly assumed that the reaction goes to completion. Indeed, previous stoichiometric calculations were based on this; when asked how much of a product is produced when so much of a reactant reacts, it was assumed 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: Collision Theory and Reaction Rates
- The rate, or speed, at which a reaction occurs depends on the frequency of successful collisions. Remember, a successful collision occurs when two reactants collide with enough energy and with the right orientation. That means if there is an increase in the number of collisions, an increase in the number of particles that have enough energy to react, and/or an increase in the number of particles with the correct orientation, the rate of reaction will increase.
- 13.2: Dynamic Equilibrium
- Virtually all chemical reactions are reversible to some extent. That is, an opposing reaction occurs in which the products react, to a greater or lesser degree, to re-form the reactants. Eventually, the forward and reverse reaction rates become the same, and the system reaches chemical equilibrium, the point at which the composition of the system no longer changes with time.
- 13.3: The Equilibrium Constant Expression
- Because an equilibrium state is achieved when the forward reaction rate equals the reverse reaction rate, under a given set of conditions there must be a relationship between the composition of the system at equilibrium and the kinetics of a reaction (represented by rate constants).
- 13.4: Le Chatelier's Principle
- The description of how a system responds to a stress to equilibrium has become known as Le Châtelier's principle: When a chemical system that is at equilibrium is disturbed by a stress, the system will respond in order to relieve the stress. Stresses to a chemical system involve changes in the concentrations of reactants or products, changes in the temperature of the system, or changes in the pressure of the system.
- 13.E: Exercises
- These are exercises and select solutions to accompany Chapter 13.