INSTRUCTOR: In this demonstration, we will look at how temperature affects the equilibrium of a reaction. The reaction we will be looking at is nitrogen dioxide going to dinitrogen tetroxide which is an exothermic reaction. Here I have three tubes filled with nitrogen dioxide and dinitrogen tetroxide. Nitrogen dioxide is brown in color whereas dinitrogen tetroxide is colorless. As I mentioned, this reaction is exothermic, which tells us that heat is a product of this reaction. Here we have a beaker filled with room temperature water. When you look at the tube in the room temperature water, you will see that it's brown in color. That tells us that there's more nitrogen dioxide than dinitrogen tetroxide. And in fact, the equilibrium for this reaction lies towards the reactant side with there being a greater amount of nitrogen dioxide than nitrogen tetroxide. Le Chatelier's principle states that if a system at dynamic equilibrium is disturbed by adding a stress, the position of equilibrium will shift to counteract that stress. A stress can be adding or removing a reactant or product. In this case, heat can also be considered a stress, by either adding more heat or removing heat. Let's first look at putting the tube in a beaker full of hot water. What do you predict will happen when I put the tube in hot water? Will it become darker in color or will it become lighter? Remember that the nitrogen dioxide is brown which is our reactant and our dinitrogen tetroxide is colorless which is a product. As you can see, the tube becomes darker brown. The reason it became darker brown is because we're producing more nitrogen dioxide, which is brown. So we've added heat, or added a product. And through Le Chatelier's principle we know that by adding a product, the equilibrium will shift to relieve that stress and thus produce more reactant, which is evidenced by the darker brown in color. Now let's instead of adding heat, let's remove heat. What do you predict will happen when I put the tube of nitrogen dioxide in dry ice and remove a product? Will it become darker brown, stay the same, or become colorless? As you can see, the tube is now colorless, which tells us that more dinitrogen tetroxide has been produced. Which makes sense, because we've put the tube in dry ice which has removed heat. Remember, this reaction is exothermic, which means heat is a product. So essentially, we have removed a product. Le Chatelier's principle states that by removing a product, we will shift the equilibrium to produce more products which is evidenced by the colorless tube that we've produced more dinitrogen tetroxide. When we compare that to our other two tubes that have mainly nitrogen dioxide, which are brown in color, you can see when we've added heat, we shifted towards reactants and the color became darker brown. At room temperature, the equilibrium still is such that we have more nitrogen dioxide than our dinitrogen tetroxide, which is why our tube is still brown.