 Today I'd like to talk to you about equilibrium reactions and some of the concepts that go along with them. Equilibrium reactions are reactions essentially that will always have both products and reactants present in them. And the reason for this is that when you have this reaction, A plus B giving C plus D, you have in the middle you have arrows pointing in both directions, half arrows. This is an indication that there is an equilibrium in existence here. The X, Y, Z and P are the coefficients that balance the equation. How this works is that A combines with B to form C plus D. After a certain quantity of C and D are formed, C and D combine to reform the A plus B. So in the system you will always have a certain amount of each of these present. These processes can cause some interesting things for chemists who want to have reactions to go to high yield. Equilibrium reactions can be challenging, but at the same time there are things we can do that will improve these. One of the things that when you work with equilibrium reactions that you need is to have what is called an equilibrium constant. And the equilibrium constant is represented in Keq. Keq is going to be defined as the quantity of products divided by the quantity of reactants and we are going to raise these quantities to the power that is equal to the subscript in the balanced equation. So for instance in this case we would say that Keq would be C raised to the Z power times D raised to the P power divided by A raised to the X power times B to the Y power. This would be your equilibrium expression. If you had values for the concentration of A, B, C, and D we could calculate what this constant would be. The Keq essentially will tell us which side of the process is favored. If Keq is large that means that products are favored. There is more of this than there is that. If Keq is small that means that your reactants are favored. The reason being is that there is a small amount of this present, most of this is present in the process. So large Keq means products, small means reactants. The reaction of nitrogen and hydrogen to form ammonia is one that you see a lot and a lot of times when it is written people don't write it correctly. The reaction between nitrogen and hydrogen to form ammonia is called the Haber process and it is a process that is an equilibrium reaction or the reaction is an equilibrium. The problem with that is that originally when this reaction was proposed and done there were low yields of ammonia, the NH3. But Fritz Haber was able to design a process where considerable amounts of ammonia could be produced from this reaction. And frankly he won a Nobel Prize for it because it revolutionized the idea of fertilizers and planting foods and things of that type. In other words feeding the world. But when we look at this the Keq expression for this would be ammonia, the concentration of ammonia squared divided by the concentration of nitrogen times the concentration of hydrogen cubed. All right. It's easy to solve for the Keq once you have your expression. All you do is substitute numbers. Over here on the left hand side I've given you some numbers that we can use. Nitrogen is one mole, hydrogen would be two moles, ammonia is one mole. And we put this into the equation and when we do that we remember to square and cube the numbers that we need to square and cube and when we calculate that we get a value of 0.125. Now these numbers that I've given you were simply examples. They would not reflect what you can actually get from this process. But given that, given the values that we have I would ask you this question. With a 0.125 would product be favored or would reactant be favored? Of course the answer is that reactants are favored because this is a small number. We talk about small and large numbers. Large numbers are 100,000 and bigger numbers than that. Small numbers are anything that's one or less. At one or less essentially you're not making much progress toward a product. So you want those numbers to be as large as they can be. But that's how you would do that. That's how you would do that. Now how was this process made efficient? How did the Haber process B become something that could be used? Well it has to do with Le Chatier's principle and I'm sure I didn't say that correctly. But that's Le Chatier. It's written here. You can see it. And his principle says that when there is a stress exerted on a system in equilibrium the system will shift in such a way as to relieve the stress. Now this has implications as far as endothermic exothermic reactions. It has implications on adding and subtracting reactants. It has implications in terms of change in pressure. In this example of an equilibrium you see that we have A plus B in equilibrium with C and heat. And believe it or not in this instance heat is a product of the reaction. Now Le Chatier's principle says that if a shift, that if a stress is applied that the system will move in the direction to relieve the stress. Alright. So let's talk a little bit about this. Heat is a product. What happens if we remove heat from the process? In that instance there'll be more A and B converted to C plus heat. So in that instance if you wanted to produce a lot of C all you would need to do would be to cool the reaction down and make the equilibrium shift this direction. Ask yourself this question. What would happen if instead of removing heat you added heat you raise the temperature of the reaction either accidentally or on purpose? What would happen? You're adding product. So in that instance you're going to shift toward reactants. So you would decrease the yield of your product if you added heat. That's because heat is a product. If we had this occurring heat plus A being in equilibrium with B what would the result of adding and taking away heat be? We ask ourselves this question. What happens is heat a product or is it a reactant? In this instance it is a reactant. So adding heat essentially will shift the reaction toward product. In an endothermic reaction which is what this is adding heat should shift in the direction of your product. So it would help you form more B. Conversely if you cool the reaction down it's going to shift it toward reactants and you're not doing that. Let's take heat out of our equation for just a moment and let's ask ourselves this. What if we had a process where we were having a simple equilibrium between A and B? What would happen if we removed B from the reaction? In that instance the reaction would shift to form more B. How else could you form more B? You would form more B by also adding other quantities of A. What if we had, what if we had this equation? This is an equilibrium and all of these are gases. All of these are gases. How would pressure affect the reaction if we have gases? Here's something to think about. On the left hand side of the equation we have seven molecules of gas. On the right hand side we have two molecules of gas. Increase in pressure will favor the side which has the least molecules of gas because that will be the least pressure. So if you increase the pressure on this system you will form more product. If you decrease the pressure on this system you will form more reactant. There are many ways that we can use Le Chatier's principle and the principle of equilibrium in chemistry and I hope that I've been able to explain some of these concepts to you so that you can better understand it. Thank you.