Writing Papers In The Biological Sciences Free Download

- [Voiceover] Let's talk a little bit about chemical reactions. And chemical reactionsare a very big deal. Without chemical reactions,you or I would not exist. In your body right now,there are countless chemical reactions going on every second. Without chemical reactions,we would have no life, we would not even have theuniverse as we know it. So what are chemical reactions. Well, they're any time thatyou have bonds being formed or broken between atoms or molecules. So what are we talking about there? Well this is maybe one of the most fundamental chemical reactions. Once again if one neveroccurred, we'd be in trouble, we would not have, wewould not have any water. But let's think about whatit is actually describing. So over here on the left-handside we have the reactants. Let me write that down. So here we have the reactants. These are the moleculesthat are going to react. And then we have an arrowthat moves us to the product. So let me do that in a different color. So we have an arrow thatmoves us to the product, or we could say the products. And so what are the reactants here? Well we have molecular hydrogen and we have molecular oxygen. Now why did I say molecular hydrogen? Because molecular hydrogen,which is the state that you would typically find hydrogen in if you just have it by itself, it is actually made upof two hydrogen atoms. You see it right over here,one, two hydrogen atoms. And what we have in orderto have this reaction, you don't just need onemolecular hydrogen and one, or one molecule of hydrogenand one molecule of oxygen. For every, for this reaction to happen, you actually have two moleculesof molecular hydrogen. So this is actually madeup of four hydrogen atoms. So let me make this clear. So this right over here, this is two moleculesof molecular hydrogen. And that's why we have the two right out front of the H sub-two. This little subscripttwo tells us there's two of the hydrogen atoms in this molecule. And then this big, this big white two that we have right over here,that tells us that we're dealing with two of those molecules for this reaction tohappen, that we need two of these molecules for every, for every molecule of molecular oxygen. And molecular oxygen, once again, this is composed of two oxygen atoms. One, two. So under the right conditions,so you need a little bit of energy to make this happen. If under the right conditions these two things are going to react. And actually it's very, very reactive, molecular hydrogen and molecular oxygen. So much so that it's actuallyused for rocket fuel. You are going to producetwo molecules of water. We see that right over here. And look, I did not createor destroy any atoms. I had one, I had one, I had one oxygen atom here. It was part of the oxygenmolecule right here, then I have the secondone right over here now. Now they are part of separate molecules. I had, I had a, I had one two, three, four hydrogens. I now have one, two, three, four hydrogens, just like that. And actually this produces a.. So we could say some energy, and I'm being inexact right over here. Some energy and then wecould say a lot of energy. A lot of energy. So this is a reaction thatyou just give it a little bit of a kick-start and itreally wants to happen. A lot, a lot of energy. So one thing that you might wonder, and this is somethingthat I first wondered when I learned about reactions, well how do, how does this happen? You know, is this a very organized thing? You know, do these molecules somehow know to react with each other? And the answer's no. Chemistry is a incredibly messy thing. You have these things bouncingaround, they have energy. They're bouncing around all over the place and actually when you provide energy, they're gonna bounce aroundeven more rigorously, enough so that theycollide in the right ways so that they break their old bonds and then they form these new bonds. So whenever you see thesereactions in biology or chemistry class, keep that in mind. It looks all neat andorganized but in a real system, these are all of these things just bouncing around in alldifferent crazy ways. And that's why energy'san important thing here. Because the more energyyou apply to the system, the more that they'regoing to bounce around, the more that they're goingto interact with each other. The more reactants you put in, the more chance they'regoing to bounce around and be able to react with each other. Now I'm gonna introduce another word that you're gonna see in chemistry a lot. This water, these two.. We see we have two water molecules here. We could call them molecules,but since they are actually made up of two or more different elements, we could also call this a compound. So water, water is, youcould call it a molecule, or you could call it a compound. So this is a molecule or compound, while this molecular hydrogen, you would not call this a compound. And this molecular oxygen,of course it's a molecule, but you would not callit a compound either. And just to get an appreciation of how much energy this produces, let me just show you thispicture right over here. That's the space shuttle and this, this big tank right over here, let me.. This big tank contains a bunch of liquid oxygen and hydrogen. And to create thisincredible amount of energy, it actually just.. You mix the two togetherwith a little bit of energy and then you produce a ton of energy that makes the rocket, thatmakes the space shuttle. Well, space shuttle'sbeen discontinued now, but back when they did it, to make it get it's necessary,it's necessary velocity. Now let's talk about the idea. So, you know, this reaction,strongly goes in this, in the direction of going to water. But it can actually go the other way, but it's very, very hardfor it to go the other way. So in general we would consider this to be an irreversiblereaction, even though it is. You know irreversible sounds like, hey you can't go the other way. It just really means that it's very unlikely to go the other way. You have to supply a lot ofenergy to go the other way. To make this reaction go the other way, you would have to dosomething called electrolysis, you provide energy, etcetera, etcetera. But in general, the waythat this is written, because the arrow is onlypointing in one direction, this is implying that it is irreversible. Irreversible. Irreversible. Which probably makes you think, well what about reversible reactions? And I have an example of a reversible reaction, right over here. I have a one bicarbonate ion. And the word ion, that'sjust used to describe any molecule or atom that has either, has an imbalance of electrons or protons that cause it to have a net charge. So this makes this an ion,and actually right over here, this is a hydrogen, this is ahydrogen ion right over here. Both of these are charged. One has a positive charge,one has a negative charge. But they are both, they are both ions. And this reactions right over here, you have the bicarbonate ionthat looks something like this. This is just my hand-drawing of it. Reacting with a hydrogen ion,it's really a hydrogen atom that has lost it's electron,so some people would even say this is a proton right over here. This is an equilibrium reaction, where it can form carbonic acid. And notice all that'shappening is this hydrogen is attaching to one ofthe oxygens over here. And this is an equilibriumbecause if in an actual, in an actual solution,it's going back and forth. If you actually provide more reactants, you're gonna go more in that direction. If you provide more ofthe products over here, then you're gonna go in that direction. And so in an actual, inan actual environment, in an actual system, it's constantly going back and forth between these two things. And different reversible reactions might tend to one side or the other. If you provide more ofthe stuff on one side, it might go more in the otherdirections because these are gonna, they're gonna bemore likely to interact, Or if you provide more of this, it might go in the other direction because these might more likely react with their surroundings ordisassociate in some way. Now just to get a sense of, you know, it's nice to kind of, youknow, are these just some random letters that I wrote here? Carbonic acid is actually anincredibly important molecule, or we could call it acompound because it's made up of two or, two or more elements, in living systems and in fact, you know, even in the environment. And even when you go outto get some fast food. When you have carbonateddrinks, it has carbonic acid in it that disassociatesinto carbon dioxide and that carbon dioxide iswhat you see bubbling up. Carbonic acid is incrediblyimportant in how your body deals with excess carbondioxide in its bloodstream. Carbonic acid is involved in the oceans taking up carbon dioxidefrom the atmosphere. So when you're studying chemistry, especially in the context ofbiology, these aren't just, you know, interesting thingsthat seem very academic. These are effecting yourreal life and your body and your environment.