19.1. The Nature of Chemical Equilibrium http://www.ck12.org
19.1 The Nature of Chemical Equilibrium
Lesson Objectives
- Define chemical equilibrium in terms of reaction rates.
- Define equilibrium constant.
- Be able to write an equilibrium constant expression for a chemical reaction using the law of mass action.
Lesson Vocabulary
- irreversible process: A chemical reaction that can only be run in the forward direction; that is, the products
do not react to form the reactants. - chemical equilibrium: The state in which the rate of the forward reaction is equal to the rate of the reverse
reaction. - equilibrium constant: The ratio of the rate constant of the forward reaction and the rate constant of the
reverse reaction. - equilibrium constant expression: The ratio of the product concentrations and the reactant concentrations,
raised to their respective exponents. - law of mass action: States that for any reaction at equilibrium, the ratio of product concentrations to reactant
concentrations (along with the appropriate exponents) is equal to a constant.
Check Your Understanding
- Can you give an example of a chemical process that is reversible?
- Can you think of a chemical process that is not reversible, or that would be very difficult to reverse?
Introduction
We have not always known that some chemical processes are reversible. In fact, not long ago, it was widely thought
that chemical processes were irreversible. For instance, the dissolving of table salt into water was viewed as a
unidirectional process; once the salt dissolved, it could not be undissolved from the solution. Dissolution reactions
were therefore viewed asirreversible processes. However, in the early 1800s, the Frenchman Claude Lois Berthollet
(1748-1822) observed a dissolution reaction that appeared to be reversible.