 Okay, this unit deals with how to describe chemical reactions to other people. In case you're not familiar with what a chemical reaction is, it's when you take one or more materials and convert them into one or more new materials. In other words, you take some chemical and do some magic on it and somehow convert it into something new. You can convert it into more than one new thing, but it's got to be at least one new thing. So as an example, this is the symbol for silver. This is the symbol for sulfur. The symbol for silver is a little bit weird unless you speak a romance language like Spanish or Italian or French. Comes from Latin, but that's beside the point. I just want you to be familiar with what element we're actually talking about. So an example of a chemical reaction is I could come up to you and say, look, I took some silver atoms. Here they are. There's a comma separating it from the sulfur atoms so they're not attached to each other. I did some magic and they ended up attached to each other. Two silvers attached to one sulfur, and this is an example of a chemical reaction because I started with one or more things. I started with two things that were separated from each other and I turned them into something new. Here's my something new. Everybody's attached so it's considered to be new. Chemical reaction or an example of a chemical reaction. I'll show you another one in a second. Here's another example of a chemical reaction. I come up to you and I say I have a bunch of H2 molecules, that's two H's stuck to each other. I have a bunch of O2 molecules, also two oxygens stuck to each other. I do some magic and I turn them into water. I rearrange the attachments so the two H's are stuck to one oxygen. Another example of a chemical reaction. If you needed to describe chemical reactions to people, you could do this. You could write the symbol for each element that you started with, write the symbol for each element that you ended up with, and you could convey that information to people. What I'm going to tell you is that this is not terribly informative. It has a little bit of information, but a lot of times, if you're describing reactions to other chemists, they want to know more information than just that. So how do you communicate, how do you tell another chemist more detail about how a chemical reaction took place, what actually happened? The way that it's traditionally done is to make something called a chemical equation. The equation basically says, look, this is much more precisely what happened in my chemical reaction. The way that a chemical equation works is this. You combine the formulas for all of the materials that you used and all of the materials that you produced, and let me show you in more detail. So the materials that you used, the formulas for the materials you used are written on the left side. So our equation is going to go here. But on the left side, you write the formulas for all of the materials that you used. So this is just an example equation that's going to show up here. On the left side, I have some H2 molecule, and I have an O2 molecule. And if you have more than one substance that you used, you write all of the formulas on the left, and you separate the formulas with plus signs. So since there are only two materials being used here, I'm just going to need one plus sign. But if I had some other material, material ABC, then I would add another plus sign. You just keep adding plus signs. The order that you write the formulas in doesn't matter. As long as they're on the left side of the equation for stuff that I used, I could have written O2 plus H2, and that would have been perfectly fine as well. On the right side of the equation, here's the right side, you write the formulas for all of the things that you actually produce. So in this case, in my example chemical reaction, I only produce one type of material, happens to be water, so I just write the formula for water. However, if I made more than just water, if I made some material that had a formula x, y, z, then I would also write the formula for x, y, z, and I would separate all the formulas with a plus sign as well. Again, the order that you write things on the right side, the order that you write the formulas on the right side, doesn't matter. And then in between the left side and the right side, in math, if you had an equation, you would put an equal sign. You can, in chemistry, sometimes that is done. It's much more common, however, to put an arrow like this. Let's see. Oh, there's my arrow. It's a much better looking arrow that the computer can make. And so the way to look at this equation is this chemical equation is saying, look, I started with the stuff on the left side of the arrow, started with H2 and O2, and I transformed it, that's basically what the arrow is saying, I transformed it into all of the materials that are written on the right side of the arrow. Here only one material is written, so I transformed those two things into one new material. So that's the very basics of how to read a chemical equation. Formulas of the materials you started with on the left, formulas of the materials you ended up with on the right, and an arrow separating them. There are some fancy names for the materials on the left and the right. The materials on the left are called reactants. They react with each other to turn into something new. You should know that term. The materials that you end up with are called products. This one is easier for me to remember because those are the things that you produce. So that's why they're called products. You should know products as well. However, what I'll tell you is that writing this is not much more informative. In fact, I don't think it's any more informative than writing this that I showed you on the previous slide. However, there are conventions for writing additional information into chemical equations. So chemical equations can contain other pieces of information about the reaction. You're going to see some of them. For example, everyone saw that amazing animation where parentheses G came in. There's a parentheses G associated with the H2. There's a parentheses G associated with the O2. That G means gas. That means the H2 molecules, they were a gas when the reaction took place. And so were the O2 molecules. Now our equation is starting to gain a little bit more descriptive information about what took place in the reaction. This triangle, if you write a triangle above the reaction, that means heat was needed to start the reaction. Not sure if you can hear my kids fighting upstairs. I'm going to go up and screen soon. So you should also know what this triangle means. A lot of times I ask that to students and they say that it means change. In math it means change. In chemistry it means you needed to heat the reactants up to have the reaction take place. You can have even more pieces of information in an equation. So before we go on to more information, let's look at this equation. This equation is saying I took some carbon, I mixed it with O2 that was a gas. I heated these things up and it made CO2, which some of you may know as carbon dioxide. That's the stuff that we breathe out as waste and the carbon dioxide was also a gas. So now we have some tools under our belt or we have some information now that can let us interpret more complicated chemical equations. Here's a new letter inside of the parentheses. It's S. You may be able to guess what that means. If this means gas, S probably means solid. So this equation now has more information. It's basically saying I took solid carbon. Maybe I took a diamond, which is made of solid carbon and mixed it with O2 gas. I heated the two up together and I made some carbon dioxide gas. So now we're sort of building up a collection of symbols that means something in a chemical equation. We've got parentheses S, we've got parentheses G, we've got this triangle over the arrow. You now know what all of those mean. Guess what? There's even more stuff you can put in. Before we go on to the more stuff, this is basically saying I took some solid aluminum. I mixed it with whatever this is. You don't really need to know what it is. It turned into this other material and I happened to make H2 gas. So more symbols, parentheses AQ. A lot of times I ask students this and I say, what does the AQ mean? And they say aqueous. And I say, what does aqueous mean? And they say liquid. And at that point I tell them that they're wrong. The AQ does stand for aqueous. However, there's a subtle point here. Aqueous basically means watery or related to water. What the AQ means is this stuff, whatever has AQ next to it, is not a liquid all by itself. However, it's dissolved in water. So that AQ basically means not a liquid, but it happens to be dissolved in water. So there's a subtle difference between what aqueous means and if something is a liquid all by itself. And you should understand that subtlety. So now we can look at this equation and we can say, well, OK, I took some solid aluminum. I mixed it with this chemical that was dissolved in water. It turned into this other chemical that was also dissolved in water. And it made some bubbles. That's what the gas means, made gas bubbles that were made of hydrogen. So now we have even more sort of symbols or tools at our disposal for reading chemical reaction. Here's a different one. I took H2 gas, mixed it with O2 gas. Maybe I heated them up and it turned into this. And now this is parentheses with a lowercase letter L. In case it's not clear what that is, that is a lowercase letter L. This L means liquid. So there's a difference between L and AQ. L means the stuff is a liquid all by itself. AQ means the stuff isn't really a liquid but it happens to be dissolved in water. So a whole bunch of little symbols now at your disposal for reading chemical equations. The punchline is that these equations are quick ways of telling you what materials you used. Those are called reactants, what materials you produced, those are called products. What the physical state of the materials was, was the material a solid, was it dissolved in water, was it a gas, was it a liquid all by itself. You also know how to interpret this symbol, which tells you whether heat was needed to make the reaction take place. So what you should know, you should basically be able to read and write a chemical equation if I give you enough information. In other words, if I show you an equation A plus B turns into C plus D. You should know that these are the reactants because they're on the left side of the arrow. You should know that these are the products because they're on the right side of the arrow. You should be able to interpret parentheses S, parentheses AQ, parentheses L, and parentheses G. You should be able to interpret the triangle over the arrow, what that means. You should also be able to write a chemical equation, but only if I give you all of the information, if I give you the formulas, if I tell you that it's a solid or that it's a gas or whatever. I don't expect you, I don't expect to just tell you a couple of chemical names and you be able to put all of the formulas together for the reactants and the products. I would have to give you very specific detailed information for you to be able to do this. So that is it for our introduction to chemical equations. Probably more difficult stuff is coming up in the next couple of videos.