 Hello. This is Kevin Conley. I'm an instructor at Foresight Tech, and I'd like to present to you another lecture on nuclear chemistry. It's time to give you the distinction between fission and fusion, two very important reactions that you'll come across in your studies of chemistry. I want to compare and contrast them qualitatively first, and then we'll take a look at some most common examples of two reactions. First of all, for fission, what you're doing is you're, what happens is a large nucleus is broken down into two small nuclei, two smaller nuclei, and normally it's a very large nucleus, something that comes from the bottom half of the periodic table. You need an initial energy source to get this to happen through a bombardment reaction, otherwise this nucleus will be rather stable or it would be a decay reaction. But fission is normally when you hit that nucleus with some energy and then it will decay, and that amount of energy can be a simple explosion with TNT or a normal type of explosive, or it can be a bombardment reaction. Either one will do. Critical mass. If you have a critical mass, you can create a chain reaction and really detonate or explode a good deal of nuclear material, otherwise you have to see to it that each one of these nuclei receives its own bombardment particle. And the chain reaction can be set up if you do have a critical mass. On the other hand, if we take a look at fusion, in fusion you take small nuclei and you push them together in such a way that they get glued and in the process they give up energy. Now that is very counter intuitive. It's due to something called the mass defect and actually that's where the concept of E equals MC squared comes from. You put in so much energy that you lose mass and you generate more energy. It's a strange process but it is also a very powerful process. As mentioned in a previous lecture, this is the process by which the stars generate their energy. They have a certain amount of mass. These protons and neutrons hit each other. They lose mass. They generate energy. And as a result, the mass of the star will decrease as time goes by. So small particles create large ones and again in this case, fusion occurs normally only in elements that are like oxygen and smaller for fusion reactions. You need an intense energy source and commonly you need to be up around 100 million degrees Fahrenheit and that temperature is nearly being reached in research labs to create fusion reactions which have been studied for the last 40, 50 years. And also you get an intense energy release on the end such as that that you see from a star for example. So there's a big payoff once you do get to that point. It's like an investment. You put this much in. You're going to get even more out but you have to have that much investment to get the result. Here's an example of the most common fusion reaction that you will hear of which is uranium which is commonly used inside of nuclear power plants. What you do is you take the uranium, you've fission it off, you get a lot of energy. The energy is within a tube and the tube heats up and then it heats up the water and as it heats up water the water is used to turn a steam turbine and then you have mechanical energy that can do various types of things. It can power a dynamo to create electrical energy for example. But the original source is nuclear and then thermal and then mechanical and then electrical if you if you so choose. So when you take the uranium 235 we're going to take a look first of all as we have before at the 92. The 92 is going to get broken up into two components and this is just what naturally does occur. 92 is going to be 36 plus 56. We have 30 and 50 is 80 plus 12, 92. So this is the way that the atomic number bounces out and you can see immediately you look on the periodic cable. 36, krypton 56, baryum. And then for the 235 it's going to be distributed among krypton and baryum but also we're going to get some neutrons out. And these three neutrons are very important because for every one of the 235s that is going to be fissioned we're going to get three neutrons. And if you happen to have a critical mass which is to say that your uranium is sufficiently dense and this is enough of it these three neutrons are going to be captured by other uranium nuclei that are nearby and this process will continue. And as the process continues as you see the first uranium creates three the next one creates another three and so forth. So if you have 12 reactions you're going to have you're going to have I don't know it's going to be like between 20 and 30 neutrons left after these so your 20 or 30 neutrons are going to be going out there to find more and more uranium nuclei so the reaction will continue. On the other hand the primary fusion reaction that you will see inside of fusion reactors that are being tested now on the earth as well as the primary cycle inside of stars is to take four nucleons which can be protons or neutrons. I could have written as two protons and two neutrons that works just the same. Four of these will create a helium plus energy. Now yes I know the number doesn't work here I could have put two protons and two neutrons but the star is really a soup of a mixture of protons and neutrons together and when they fuse together here even though it looks like I'm just conserving I would be conserving the charge in the mass numbers an incredibly large amount of a lot of energy comes out of this. This has to do with something called a mass defect which is very exciting but it's beyond what you're going to be seeing in your class here. I look I suggest you look into the stellar process here it's really pretty cool but for now you get to see the distinction between fission large things breaking up into small ones and fusion smaller things combining to be bigger ones.