Introduction

Not every change around you runs to completion in one direction. A banana ripening or iron rusting never reverses, but plenty of everyday processes -- even one happening in your own bloodstream right now -- settle into a balance between two opposing directions instead.

What this unit sets out to do. By the end of it you should be able to:

• describe what equilibrium means, and explain the dynamic nature of equilibrium in both physical and chemical processes;
• state the law of mass action, and deduce the expressions for the equilibrium constants $K_C$ and $K_P$;
• establish the relationship between $K_P$ and $K_C$;
• use the equilibrium constant to predict how far a reaction proceeds;
• state Le Chatelier's principle, and explain how various factors disturb a system at equilibrium;
• derive the Van't Hoff equation.