Introductory statistical mechanics is studied for a simple two-state system using an inexpensive and easily built apparatus. A large variety of demonstrations, suitable for students in high school and introductory university chemistry courses, are possible. This article details demonstrations for exothermic and endothermic reactions, the dynamic nature of equilibrium, and Le Chatelier's principle. The demonstrations show how the equilibrium changes as the temperature, energy, and entropy are varied. (Contains 5 figures.)