le chatelier's principle is one of the most important in chemistry. this principle allows chemists to manipulate reversible reactions. let's see le chatelier's principle in action by looking at this reversible chemical reaction. in each of these beakers, i have cobalt compounds. in this one, almost all of the cobalt ions are attached to water molecules, so it's pink. in this beaker, almost all of the cobalt ions are attached to chloride ions, so it's blue. since this is a reversible reaction, we should be able to interchange between these two colors. i'll put some pink solution into this beaker. and then i'll add chloride ion. oh, there's the blue color. and then watch what happens if i add water. it goes back to pink. le chatelier's principle tells us that if we add chloride ion, a reactant, then the equilibrium will shift to the product side to use up as much of that chloride as possible. then if we add water to the system, the equilibrium will shift to the reactant side to use up as much of that excess water as possible. the ability to shift the po