It is possible to predict what will happen to a chemical reaction at equilibrium as conditions change based on collision theory. It is easier to predict using Le Chatelier's Principle. Le Chatelier's Principle says when stress is applied to a system in equilibrium, the reaction will shift in a direction that relieves the stress, and a new equilibrium will be established. Stresses for chemical systems can be changes in temperature, pressure, or concentration. This PowerPoint presentation explains how to use Le Chatelier's principle to predict the effect of stresses on chemical reactions at equilibrium. Worksheets on this topic are available free of charge on my website at www.evanschemistrycorner.com.