The Foundations of Chemistry

OUTLINE

17-1 Basic Concepts

17-2 The Equilibrium Constant

17-3 Variation of Kcwith the Form

of the Balanced Equation

17-4 The Reaction Quotient

17-5 Uses of the Equilibrium

Constant, Kc

17-6 Factors That Affect Equilibria

17-7 The Haber Process: A Practical

Application of Equilibrium

17-8 Application of Stress to a

System at Equilibrium

17-9 Partial Pressures and the

Equilibrium Constant

17-10 Relationship between KP

and Kc

17-11 Heterogeneous Equilibria

17-12 Relationship between 
G^0 rxn

and the Equilibrium Constant

17-13 Evaluation of Equilibrium

Constants at Different

Temperatures

OBJECTIVES

After you have studied this chapter, you should be able to

• Explain the basic ideas of chemical equilibrium


• Explain what an equilibrium constant is and what it tells us


• Explain what a reaction quotient is and what it tells us


• Use equilibrium constants to describe systems at equilibrium


• Recognize the factors that affect equilibria and predict the resulting effects


• Use the equilibrium constant expressed in terms of partial pressures (KP) and
  relate it to Kc


• Describe heterogeneous equilibria and write their equilibrium constants


• Use the relationships between thermodynamics and equilibrium


• Estimate equilibrium constants at different temperatures

BASIC CONCEPTS

Most chemical reactions do not go to completion. That is, when reactants are mixed in

stoichiometric quantities, they are not completely converted to products. Reactions that

do not go to completion andthat can occur in either direction are called reversible reac-

tions.

Reversible reactions can be represented in general terms as follows, where the capital

letters represent formulas and the lowercase letters represent the stoichiometric coeffi-

cients in the balanced equation.

aAbB 34 cCdD

17-1

Gaseous ammonia, NH 3 , and
gaseous hydrogen chloride, HCl,

react to form solid NH 4 Cl, the
white smoke. In the reverse

reaction, solid NH 4 Cl decomposes
when heated, to form gaseous NH 3

and HCl.

See the Saunders Interactive
General Chemistry CD-ROM,
Screen 16.2, The Principle of
Microscopic Reversibility.