 So chemical reactions. Chemical reactions happen when two groups of molecules basically swap atoms and you end up with something different on the other side of the chemical reaction. When I blow up a gummy bear, it kind of looks a little something like this. All the energy that is stored in the gummy bear's chemical bonds is actually released into the universe. Thankfully, our bodies handle that release of energy a little bit different than an explosion like this. But let's take a look at the basic rules of talking about chemical reactions. First of all, you have reactants and hopefully this is also a review. You have reactants and you have products. And there's something that happens in a chemical reaction that we'll talk about in just a second. So I'm going to give you an example of a chemical reaction that you already are like, pfft, I'm all over that action. And that is the chemical reaction of photos, I mean of cellular respiration. You don't photosynthesize. I wish I did. Cellular respiration is glucose C6H12O6 plus. Now where do we get the glucose? I feel like we've talked about this already. The glucose comes from the food you eat and oxygen. Where do we get that? We breathe and that's why we don't smoke. And if you're in physio, you're not allowed to smoke. In anatomy, I'll give you the pass. You can quit smoking after you're finished taking anatomy. But in physio, no, you're done. It's time to stop smoking. Yeah, and I will happily help you out with that. Better stop. Focus. Now, glucose and oxygen, if you let them go through the chemical reaction, thanks to your mitochondria, we actually are going to get out carbon dioxide, how to get rid of that, plus water, how to get rid of that. Let's not talk about that. And what? In us, we get energy out. We get ATP. ATP was one of my favorite molecules. That's where all of our energy comes from. Now, ATP, yes, you need ATP to carry out most of the chemical reactions in your body. You need energy to make them happen. In fact, when we go into the mechanics of how these transporters are working and how the receptor sends the message, ATP is often involved. You need a source of energy to make this stuff happen. So this chemical reaction is totally relevant. These are the products. You know they're the products because of the direction that the arrow is pointing. These are my reactants. Guess what? I'm not going to tell you the next part. I could flip the whole chemical equation and have the arrow just going in the other direction and it's the same thing. These are still my products. I mean my reactants. And these are still my products. And that, like, get comfortable with that. It doesn't matter which side it's on. I think convention because we read from left to right. The convention is to write it from left to right. But the fact is it could go back the other direction as well. And that leads us right into our next topic. Now, just because I'm here, since I'm here, let's talk about what is the six? That's how many carbon atoms we have. We've got six carbon atoms, 12 hydrogen atoms, and six oxygen atoms in one molecule of glucose. I'm not going to get too crazy about counting atoms, but it's something that you should be able to look at when I give you a molecule like this. You should be able to look at that and go, okay, I know what that is. Do you really know what an atom is? Well, we're not going to get crazy on that one either. Chemical bonds, what? We're not going to get crazy on that either. You can take chemistry for that. In the meantime, we're just going to imagine those little balls that get stuck together with these chemical bonds and make a shape that's going to do something for us. Let's talk about what happens if this particular situation, the reaction happens in the other direction.