Chapter 17: Chemical Equilibrium

Irreversible Reaction

A reaction that can occur only in the forward direction.

Reversible Reaction

A reaction that can occur in both the forward and reverse directions.

Chemical Equilibrium

The state in which the forward and reverse reaction rates are equal, and the concentration of each substance remains constant.

Equilibrium Constant (K_eq)

A numerical ratio of product concentrations to reactant concentrations at equilibrium.

Characteristics of Reversible Reactions

• Reactants and products exist together in a mixture.
• The ratio of reactants to products depends on the relative speeds of the forward and reverse reactions.
• Changing the rate of either reaction alters the equilibrium position.

Examples of Chemical Equilibrium

• Evaporation and condensation of water.
• Dissolution and precipitation of a solute in a solution.
• Formation and decomposition of calcium carbonate.

Equilibrium Constant

Expression

$K_{\mathrm{eq}}=\frac{\mathrm{[products]}}{\mathrm{[reactants]}}$

Interpretation

• K_eq > 1: Products are favored; equilibrium lies to the right.
• K_eq < 1: Reactants are favored; equilibrium lies to the left.

Types of Equilibria

• Homogeneous Equilibrium: All substances are in the same state of matter.
• Heterogeneous Equilibrium: Substances are in different states of matter (e.g., solids and liquids).

Questions for Students

1. Define reversible and irreversible reactions with examples.
2. What is chemical equilibrium, and how is it achieved?
3. Write the equilibrium constant expression for the formation of ammonia from nitrogen and hydrogen.
4. Explain the difference between homogeneous and heterogeneous equilibrium.
5. How does the value of K_eq indicate the favorability of products or reactants?