 Today, I'd like to talk to you about reaction rates. Reaction rates are the rate at which reactants are turned into products or the rate at which products are formed. And there are a number of factors which influence reactions. There are a number of factors which influence reaction rates. Before you can evaluate a reaction rate, you have to have a reaction. And so, on the board, I have a few things that will help us determine whether or not a reaction is going to occur. The first is energy. A reaction has to have a certain amount of energy. The energy of the reactants has to be sufficient when they come together to cause this reaction to occur. The second thing that has to happen is that when two chemicals react, they have to be properly oriented. In other words, if you were trying to hook up a trailer hitch, you have to align the trailer hitch in a certain direction in order for it to fit. Reactions in some instances are similar to that. And that one particular reactant will need to react with a particular part of the site in a particular way. So orientation is a factor. The other thing is that you have to have a lot of collisions taking place for these things to react. Not every collision between two molecules is going to cause a chemical reaction. So if we want to increase the rate of reaction, what kind of things do we do? Well the first thing you can do is you can increase the temperature of the solution. In doing that, the molecules will move faster and they will have a higher kinetic energy which will give any collision a better opportunity to produce a product. That's the first thing. The second thing you can do is that you can increase the quantities of the reactants that are present. And a lot of times I tell my students this. What would happen if I put two of you in a room and I blindfolded you and told you to walk around the room until you ran into each other? And the probability of the two of you hitting one another is probably not great. But if I blindfolded 20 of you and put you into this room, the probability of hitting somebody else is greatly increased. So by increasing the concentration of the reactants, you increase the probability that you're going to have a connection and a reaction. Of the three, the orientation is the one that we as chemists would have more difficulty controlling. But we can look at energy and we can look at collisions. And energy is actually fairly important. All you have here in front of you is called an energy diagram. And the energy diagram shows us the different areas where we relate energy to reactants and products. Typically, your reactant will have an energy which is going to be low. We consider it to be lower. The energy can be high. It can be up here. But typically this is the traditional thing you see. The reactant will gain energy. And as it gain energy, it approaches what we call the transition state. And once you reach the transition state, it has enough energy to make it over into a product. Doesn't necessarily mean that you're going to get a product, but it at least means you have the energy needed. But once you pass that transition state and you're here, pretty much you're going to form a product. Now the amount of energy that it takes to raise the reactant from its reactant state up into a transition state is called the activation energy. And it is actually this area from here to here. The difference in those two areas is your activation energy. Another factor that's important when you're talking about energy of reactions is the idea of what is energy. Well the energy of a reaction is always calculated using the energy of the products minus the energy of the reactants. And so when we do that, what we find is that if you have a product which has a higher energy than a reactant, that process is going to have a positive energy. What if we had a situation where our product had an energy down here below the reactant? In that instance, your energy output is going to be negative, meaning that you're going to actually require less energy overall to produce the product than you're putting into the process. So when you have reactions that are set up this way, you can determine whether or not you're going to need to add energy continuously to make these things happen or whether or not once they begin they will continue to function. The way we like to refer to our reactions in this instance is are they exothermic or are they endothermic? For an exothermic reaction heat is lost during the reaction and the endothermic heat is gained in the reaction. In the exothermic reaction, the energy of the products is less than the energy of the reactant and the endothermic energy of the product is greater than the energy of the reactant. So as we look at a chemical reaction like this, let's think about some examples that you might see of exothermic and endothermic reactions. An endothermic reaction is typical of the new type of ice pack that are used for athletic games. These ice packs are essentially chemicals that when they're shaken or pushed around in a bag, the bag begins to get cool. And the reason is that there's a reaction taking place inside the bag that's requiring energy. It's moving the energy away from the outside of the bag and thus the outside of the bag is getting colder and you can put that on some type of injury and it will help it. For those of you who have ever experienced it, a good example of an exothermic reaction is the baby bottle warmers that people use. And essentially it has a reaction inside that when it is activated it will produce heat and it will essentially warm the milk slowly so that the baby will be happy with not having cold milk. Obviously, other examples of the exothermic reaction would be a campfire or a charcoal grill or something like that where heat is liberated during the process. I hope that this discussion has helped you with the idea of chemical reactions and thank you so much.