Chemical Equilibrium

10

These skills are usually tested on the SAT Subject Test in Chemistry. You
should be able to...

Explain the development of an equilibrium condition and how it is

expressed as an equilibrium constant, and use it mathematically.

Describe Le Châtelier’s Principle and how changes in

temperature, pressure, and concentrations affect an equilibrium.

Solve problems dealing with ionization of water, finding the pH,

solubility products, and the common ion effect.

Explain the relationship of enthalpy and entropy as driving forces

in a reaction and how they are combined in the Gibbs equation.

This chapter will review and strengthen these skills. Be sure to do the
Practice Exercises at the end of the chapter.

In some reactions no product is formed to allow the reaction to go to completion;

that is, the reactants and products can still interact in both directions. This can be
shown as follows:

A + B C + D

The double arrow indicates that C and D can react to form A and B, while A and
B react to form C and D.

TIP

Equilibrium is reached when the forward and reverse reaction rate are equal.

REVERSIBLE REACTIONS AND EQUILIBRIUM

The reaction is said to have reached equilibrium when the forward reaction rate
is equal to the reverse reaction rate. Notice that this is a dynamic condition, NOT