http://www.ck12.org Chapter 19. Chemical Equilibrium
19.3 Factors Affecting Chemical Equilibria
Lesson Objectives
- Determine whether various changes would alter the position of an equilibrium.
- Describe Le Châtelier’s Principle, and use it to predict the direction that a reaction would shift in response to
various changes.
Lesson Vocabulary
- Le Châtelier’s Principle: States that when a chemical system is at equilibrium and is disturbed by a stress,
the system will respond by attempting to counteract that stress until a new equilibrium is established.
Check Your Understanding
- Write the equilibrium constant expression for the following chemical reaction: 2NOBr(g) 2NO(s)+Br 2 (g)
- If Kcfor this process is 0.0142, would you expect the reaction to be reactant-favored or product-favored?
Introduction
So far you have learned about what chemical equilibrium means and how to calculate an equilibrium constant for a
reaction based on reaction rate and reactant component concentrations. In order to establish chemical equilibrium,
the rates of the forward and reverse reactions change until they become equal. In this lesson, you will learn how a
chemical reaction maintains equilibrium when a stress is put on the system.
Le Châtelier’s Principle
Equilibrium represents a balance between the reactants and the products of a chemical reaction. Changes to the
conditions of the system can disturb that equilibrium. When this occurs, the system reacts in such a way as to restore
the equilibrium. However, the position of equilibrium will be changed following the disturbance. In other words,
the response of the system involves a change in the amounts of the reactants and products. Some will increase and
some will decrease until equilibrium is reestablished.
Chemical equilibrium was studied by French chemist Henri Le Châtelier (1850-1936), and his description of how
a system at equilibrium responds to a change in conditions has become known asLe Châtelier’s principle. This
principle states that when a chemical system is at equilibrium and is disturbed by a stress, the system will respond
by attempting to counteract that stress until a new equilibrium is established. Stresses to a chemical system include