 Alright, this video is all about everything you need to know about potential energy diagrams. So this is a potential energy diagram. This is the potential energy diagram for the combustion of methane. It's a hydrocarbon reactant with oxygen producing carbon dioxide and water. That is the general format of a combustion reaction, CH4's methane. So this is the combustion of methane. The first thing you have to be able to tell from one of these potential energy diagrams is what type of reaction is taking place. Whether it's endothermic or exothermic. And for that, we have to look at the relative energies of our reactants and products. Reactants are always on the left side of the potential energy diagram because this is basically the progression of the reaction we have here. As we move along the x-axis, the reaction is moving forward and you start with reactants. That's why they're always over here on the left side. Over on the right side, you find your products. So we look at the relative energies of our reactants and products and we can see our reactants have more potential energy than our products do. This is what we would call a downhill reaction. A downhill reaction is exothermic. So again, you look at your energy, you compare your reactants and products, and if you're going down, it's exo. If you're going uphill, it would be endo. Let me draw you a real quick example of what that would look like. You'd have your potential energy on your y. You'd have your reaction progression on your x. It would look like this. And again, your reactants are always on the left because that's what you start with and your products are over here on the right. And as you can see in this case, we're going up. If we were going uphill, the reactants are lower than the products than it would be endothermic. And again, this particular one, the one I'm working on is exo because it's downhill as we go from reactants to products. The next thing you'd have to be able to do is be able to figure out the energy of your reactants and products with the actual values of those energies are. I'm just going to throw some numbers on here for the sake of working with the graph, being able to get some actual numbers off of it and everything. The energy of your reactants is A. This is reactant energy. It takes us from the x-axis up to where the reactants are. And our reactant energy in this case is 60, whatever it is. It might be kilojoules. It might be joules. Those are the two most common. So we'll say this is joules. My reactant energy would be 60 kilojoules. Again, it's just how far up that y-axis we've gone. My product energy would be E. And again, we're looking at the distance from this up to where the products are. Good thing you're not a social studies teacher. Me either. We wouldn't be doing this video. So again, from the x-axis up to where the products are, E is our product energy. And again, using the numbers I wrote in here. I would say that is 30 kilojoules. And like I said, I can see how I've gone downhill. I've went from 60 kilojoules to 30 kilojoules. That's this downhill idea. And that's how I know it's an exothermic reaction. You need to know what B is. B measures from the reactant energy from our 60 kilojoules to the highest point on our curve. B is what we call activation energy. According to collision theory, when the particles collide, they have to have a certain amount of energy for the reaction to progress. That amount of energy is the activation energy. It's the energy needed to activate the reaction. In this case, what we would do is subtract the big number from the little number, 80 minus 60. And we'd say it's 20 kilojoules of activation energy. The difference between your highest point and your reactants is the activation energy. So again, I just subtract 80 from 60, 20 kilojoules of reaction energy. In other words, if my reactants don't have 20 kilojoules, they don't make it over the hump. They roll back. Nothing happens. To get over the hump and down to where the products are, we have to have 20 kilojoules of energy to get over the hill. That's activation energy. The only other one on here that we need to really be able to work with is D. D is delta H, the change in energy that occurs. D is change in H's heat in this case. That's the change in the heat energy that's happening in this reaction. And the way we figure this one out is we always do the products minus the reactants in that order. So my products are 30. My reactants are 60. That is negative 30. Now what the negative sign means here is that that energy has been removed from the reactions. That energy has left the reaction. It's kind of like when you balance your checkbook. When you take something out of it, you subtract it. So if you went to the store and spent $10 in your checkbook, you'd write minus 10 because you took the $10 away. This is removing energy from the reaction. And so we're taking it away and subtracting it. So we end up with a negative number for an exothermic reaction. And again, this is just telling us how much energy was released by this reaction. 30 kilojoules has been released from that reaction. And that would be in form of heat most of the time, which would cause the temperature of my container to go up. Now on the end of thermic one, everything's still the same. Our reaction energy is still from the x-axis up to where the reactants are. My product energy, which was E in the previous one, is still from the x-axis up to where my products are. My activation energy is still from the reactants to the highest point. That doesn't change at all. And my delta H is still just between my reactants and my products. But there will be a few things that you'll notice that are different. When I look at the activation energy in the exothermic reaction, I can see that it's pretty small. Because my reactants are relatively high. They're close to the peak already. When I look at an endothermic reaction, that activation energy is much, much larger. Because my reactants are lower. The other thing that you'll notice is when you go to do your delta H, it is still P minus R. And so let's say this is at 20, and let's say this is at 40, and for fun, let's say this is at 80. I still find this the same way. My activation energy is still the big number, the peak, minus where my reactants are. My activation energy in this case would be 60 kilojoules. You've got to appear it was only 20, because this is exothermic, and the activation energies are lower in exothermic reactions. Here it's a much bigger number, but I still find it the same way, peak minus reactants. But when I go to do this one, I'm going to get a positive number. And what that positive number means is I have to add that to my reaction. I have to add it. I have to absorb it. It's endothermic. It's like when you put money into your checkbook, and you're going through your check register, it would be a plus. So if you went and deposited $10, you'd write that in as plus 10. Well, I'm depositing 20 kilojoules of energy. I have to put it into my reaction, so I see it as a plus sign. Exothermix, a negative delta H, because you were moving it from the reaction, you're taking it away. It's like taking money out of your checkbook, you subtract it. Endothermix, you add it, so you get a positive number for delta H. And that should be it. That should be about everything. You have to pull off a potential energy diagram.