According to Le Chatelier's Principle, if stress is applied to any system of reactions at equilibrium, the equilibrium will adjust or shift itself in such a direction so as to reduce the effect (or relieve the stress) of any change in conditions. In this series of activities, students put Le Chatelier's Principle to the test. They learn the four important factors that can disturb the equilibrium of a chemical reaction: concentration, pressure, temperature and light. Your students will discover that chemical reactions do not always go to completion and that all are somewhat reversible. Students encourage one of two simultaneous chemical reactions which cause the equilibrium of the mixture to change. This Lab-Aid is complete for 50 students.