Endothermic and Exothermic Reactions

Hi, it's mister Anderson, and this is chemistry essentials, video 33. It's on endothermic and exothermic reactions. If you understand that therm means heat and exo means to exit or to move out, it's pretty easy to break down these reactions. So an exothermic reaction would be one where heat is being released from the reaction. So a thermite reaction right here. You can almost feel how hot that is is a reaction where we're releasing energy, releasing heat from the reaction itself. And likewise, if we have an endothermic reaction, that's going to be one where the reaction is taking in heat. And so in a cold pack like this, there's a combination of water and ammonium nitrate that reaction is consuming heat. It's taking it from the surroundings. And so it's going to feel cold over time. And so you really have to understand what is the system and what are the surroundings. And so in a reaction, the system is going to be where the reaction is taking place. So in the chemicals themselves, and then the surrounding is going to be outside of that. So if we have a change in heat, that's either going to be an exothermic, or an endothermic reaction. Now in the lab, we can't really see at the level of the atoms. And so we have to view it macroscopically. And we do that by simply measuring the temperature change. And so in exothermic reaction, we're going to find that heat is being released from that reaction to the surroundings. And in an endothermic, it's actually being absorbed. Now a really neat way to observe this is to use a model, is to use an energy diagram like this. And so the way it works is that the energy progress will be going along the X axis. And then the amount of energy in the reactants and products is going to be displayed. And so in an exothermic reaction, what you will see is a downhill reaction. In other words, the reactants are going to have more energy than the products. Now, where is that energy going? Where is that heat going? It's going to the surroundings. And likewise in an endothermic reaction, the reactants are actually going to have less energy than the products. And so they are consuming that energy. And so let me give you an example of that. Here's that exothermic reaction again. We've got a thermite reaction where we're taking iron oxide and aluminum, and we're making iron and aluminum oxide. Now this is a really intense reaction, and it's actually it provides the oxygen in this form of combustion. And so this should be able to work even underwater. But if we were to look at the energy diagram of this over time, as it progresses, we'd find that these reactants, the iron oxide and the aluminum, have a higher energy. In other words, there's more energy locked in those bonds than we are going to have in the products. And so we can see this as a downhill reaction. Now what's going on? Why do we see this increasing energy here? Remember, we have to start pressuring those bonds, put a little bit of pressure on it before we can actually have them break apart. And we get that exothermic reaction. And we call that an activation energy. So you're going to put a little bit of energy into the system, but you can see that we're going to net energy coming out of that. And so that's going to be measured in heat coming off that there might reaction. Now, if we look at an endothermic reaction, again, this would be like solid ammonium nitrate, and we're just combining it with water. So we're going to make ammonium and nitrate ions. In that case, what we're doing is the reactants are actually going to have a lower amount of energy than the products. And so you can see here is our activation energy. But this is an uphill reaction. In other words, it requires energy. It requires heat. Where is it getting for that heat? It's getting it from the surroundings. And so when we're measuring ectothermic or exothermic and endothermic reactions in the lab, we really stuck with the temperature itself. And so if I wanted to measure a reaction like this, let's say I take a chemical and I mix it with water or mix it with another chemical, I can simply use a thermometer to measure what's going on. And so I see a decrease in that temperature. Okay, so what's happening? It's actually consuming heat from the surroundings. And so this would be an endothermic reaction. And so that's pretty simple. What you should be able to do after you're done is to generate a relevant symbolic and or a graphical representation of the changes. Remember, we use an energy diagram to do that. It's all about the heat, and I hope that was helpful.