Low cost easy lab to demonstrate the effect of pressure on chemical equilibrium, one of Le Chatelier's principles. Students dissolve Alka Seltzer in test tubes, put a stopper with a hole on top and cover the hole and notice how the reaction changes when the pressure increases and when it decreases. Includes 5 student pages and 2 pages of teacher instructions and answer key. Student pages include data tables, modeling, research, presentations of models, refining models, CER (claim, evidence, re