 Okay guys, good morning. Good morning. Yeah happy Monday morning Did it scare you is that what you were saying all those people come into your door Okay, so hopefully everybody had a happy Halloween yesterday got a lot of candy Got a lot of studying. Yeah, I saw you were online very late last night Okay, anyways Ladies and gentlemen, if you don't mind Everybody came to hear me talk today not each other, right? So yeah, so we might as well get started with listening to me, right? Okay, so if you recall Last time we talked about reaction rate This was a problem that was given at the end of lecture last time Okay, so a solid Sodium was put into pure water all the sodium had reacted after eight seconds And the concentration was found to be 0.001 3 molar how do you figure out this problem? So let's go ahead and figure out. Well, what's the average rate here? All right, so what is the formula say so it says the concentration of a2 minus the concentration of a1 so concentration a2 so this is concentration of a at time 2 Minus the concentration of a at time 1 and remember this is the general reaction a goes to be so we're looking at the reactants here, okay, and we want to do Change of time, so we're going to do time 2 minus time 1 And then we say And then let's figure out what these variables are so what's concentration a1 What is that going to be does anybody know? Since everybody did this problem over the weekend like we were supposed to write Everybody should be telling me what's going on. So what's concentration a1? Okay, good job guys. So why don't you guys do this on your own? and We'll go over it tomorrow when you guys can tell me what the answers of this are okay Okay, so let's start talking about reaction mechanism then So a reaction mechanism is step-wise changes that reactants undergo in their conversion to products Okay, I'll show you a reaction mechanism And we want to think about So I'll erase this stuff. So if we think about reactions going from a to b okay We briefly mentioned this at the end of last period That a reaction going to a and b that's just like watching a Race but not watching what happens in the middle That's only watching what happens at the beginning of the race and at the end of the race So it's like two snapshots like what's the starting order and who won? Okay, but a lot of interesting stuff could happen in between the beginning and the end of a race right I can imagine like I Don't know like a NASCAR race or something like that probably people Watch it more often than not to see what happens in between What happens at the starting and the ending point right then they enjoy watching what happens in the middle Okay, yeah people wreck right so that would be like the Reaction mechanism, okay, so what we've been showing so far is just watching Okay, so this is what happened at the beginning. This is what happened at the end. That's not very interesting Okay, so let's start talking about what happened in the middle. Okay? so what could happen in the middle is a Could go to like intermediate one and then intermediate one could go to intermediate two Intermediate two could go to Intermediate three so on and so forth Until we get to be okay So if we just took these two snapshots We wouldn't know anything about intermediate one two and three. Okay, just to beat a dead horse Okay, so the stepwise changes that the reactants undergo on their way to conversion to products So a reaction mechanism often is expressed as a number of processes that must take place for these reactions to occur So we got to make a few assumptions when we're talking about reactions Okay, so the first assumption is that the reactant particles must collide with one another in order for a reaction to occur Okay, they can't just shout at each other and react Okay, they actually have to come into contact with each other With enough speed to smash into each other break bonds and form bonds Okay, so the reactant particles must collide with one another In order for the reaction to occur this of course is if you have two reactant particles For a decomposition reaction, of course, you're only going to have one reactant, right? So you don't need it to smash into anything else. You just need to give it enough energy to for those bonds to break Okay, this is the assumption that we're talking about if we have something more than one reactant, right? But anyway, so molecules can't react with each other if they don't come into contact with each other and During collisions some bonds are broken Atoms are exchanged and new bonds are formed. Okay, let's look at a proper reaction mechanism So We'll look at Bromo methane Reacting with sodium hydroxide to make methanol. Okay. Let's look at this reaction So you guys remember what a wedge bond means, right? Okay, and a dash bond, you know that too, right? Okay, cool. Okay, so the reaction that I'm going to write here is going to be CH3Br This is the liquid plus NaOH We can make this aqueous goes to CH3OH Plus Na, oops CH3OH liquid plus MABR Aqueous is good enough for me Okay So when we put NaOH into water Everybody probably understands hopefully that it's going to dissolve into water breaking into its two constituent ions Na and OH Okay So if you really wanted to think about it that would be the first step of the reaction mechanism But not the reaction mechanism proper. Okay, because the OH is the only thing that really reacts So we're going to have floating around in solution and Na plus ions and OH minus ions like that Here let's just draw this bond out Okay, so this reaction that we're about to do is not like this reaction where there's One two three four five or whatever steps. Okay, this is a one-step reaction But you can actually see the reaction mechanism So what's going to happen is? The electrons on this oxygen are going to want to attack That carbon there smash into it like that and knock this bond But you can really this really emphasizes what happens. We're Making a bond and we're breaking a bond. Okay, so let's look at the way that we've made the bond and broke the bond okay, so Hopefully everybody can see that we've made a bond in between this oxygen and that carbon. Okay, we've also Broken a bond Between that carbon and that bromine. We broke that bond there So this is a one-step mechanism All that happens is the one piece smashes into the other piece and knocking the Third piece away. Okay, so can everybody see what's going on here and see how we're Describing what is actually happening during the reaction as opposed to just saying what we set up here This now this Okay, so now we're actually saying this is how this molecule came into being right That makes sense, right? This is like a boxing match right instead of just watching two people stand here And then one person fall down right or one person on the ground you can see the actual punch that happened Okay to knock the person down. This would be the punch that happened So here we're seeing here the reactant particles Collide with one another these arrows are describing the motion of these reactant particles We're showing the bonds being broken right here. We see this bond is being broken We see this bond is being formed Okay, so we also assume that the reactant particles collide with a certain amount of energy So the reaction will occur if they don't if you it's like in the boxing match if the guy just taps the other guy It's not going to fall down right so you got to have enough energy to knock the guy out And in some cases reacting particles must be oriented in a specific way for the reaction to occur So like for this reaction This reaction only will occur if this oxygen hits this carbon at this spot if this oxygen came over here Whoops And ran into that bromine right there this reaction wouldn't occur Okay, because this oxygen wants to make a bond with this carbon if it's hitting it here It can't make a the reaction. It's like the boxing Analogy again, right if the boxer that wanted to win hit the other boxer on his foot, right? Probably wouldn't knock him out. Okay, so you got to hit him in the right spot. Okay, not in the little toe Okay So what we've just described is known as an effective collision okay So at all temperatures above absolute zero bonded atoms of molecules vibrate and stretch Okay, so what happens is you can see the bond here This is the average length of the bond, but when you've got some sort of temperature involved they kind of Stretch and bend and do all weird stuff. Okay, but they don't stretch enough to where the bond breaks Okay, so a bond is like kind of like I don't know Like a spider web or something that you that you get stuck to your hand, right? So when you get stuck to your hand, right? You pull it and pull it and pull it until it breaks Okay, and that's when the reaction occurs. Okay, but what happens is they can pull and stretch and bend without Actually breaking. Okay, and this is the actual total energy that the molecule actually has within it Okay, so when we talked about bonds being stored chemical energy That's what they're doing is using that energy just bouncing back and forth. Okay Kind of not really though metal is not covalent bonded together Okay, so you got to think of things that are covalently bonded together. That's why the Ozone layer shields us from UV radiation in the Sun is because when the Sun's UV radiation Hits that ozone it instead of you know breaking to form oxygen What happens it just stretches a little bit and then goes back so it absorbs that energy Okay, so this is covalent bonding. We're talking about not Metallic bonding or ionic bonding This is also like why You see colors Okay, so the colors are Absorbing that light and then reflecting Reflecting the light that they're not absorbing back and that's the colors like your shirts Not absorbing purple and your shirts not absorbing green. Okay, that's why we see those colors Okay, but this is what happens in covalent molecules. They stretch and bend and do all this stuff So they have a certain amount of internal energy is what we call that. Okay This internal energy can be increased by Collisions, okay, so it's just like you can imagine You know you can pull something apart harder or push it together harder and that's giving it even more energy So this Results in more vibration more vibration more vibration until the thing actually breaks Okay So if it breaks then we call that a reaction. Okay So it's not anything special. We have all these special names for all of this mundane things that actually are happening So if we look at this reaction here CH4 and O2 Are the reactants? So we'll do a less detailed analysis than we have done here But we got CH4 Notice this is the Lewis structure that I'm drawing here and O2 Like that Okay. Well, we've got two O2 molecules like that We call it a reaction Right Okay, so what happens? Whoops CO2 H2O Okay, so plus some energy So are these molecules on the left side of this arrow the same as on the right side of the arrow? No, what about everybody else that said didn't say anything No, right, so hopefully everybody can see that the left side and the right side are different. Okay, so But what is the same on the left and the right side? What is the same? So the elements specifically what that there is carbon hydrogen and oxygen? Okay, that's the same. What else is the same? The number of the Specifically yeah, that's what I was looking for right is that the number of atoms The particular atoms is the same on the left and the right side of the equation, right? but What's different about them? Yeah, so they're so Another way to say that right maybe in more layman's type terms is that They're arranged differently, right? They're all arranged differently Okay, so what must have happened from going from here to here? Bonds bonds had to be broken in this thing here, right because there's none of that stuff over here Right and since there's only got one carbon here and one carbon here We know that that carbon must have had some Oxygen's react with it right and also have those hydrogen somehow fall off of it and those hydrogens Since they're not attached to that carbon anymore, but are attached to this is oxygen's over here Something must have happened right so like was said bonds were must have been destroyed and Created or broken and formed right? so in this case the CH single bond was broken and the O double bond was broken O2 double bond was broken and The C double bond O was formed and the OH bond was formed too So energy is required to break the bonds. We'll talk about this in more detail in a second This energy comes from the collision of the molecules, okay? so it's just like the collision of the Boxers hand to the jaw of the other boxer that gives the energy to knock the guy out Right the energy that comes from the Are the it's necessary to break those bonds comes from the things? Smashing into each other and we call this an effective collision okay, so Why does any reaction occur? Okay, so this is is the next question. Why do these reactions occur to begin with? Can anybody think of a reason why reactions occur? There's no wrong answers right now. Well, I mean there's wrong answers, but don't worry about it But don't worry about getting them wrong. Okay, so can anybody think of any reason why a reaction would occur? Okay, so okay. Yeah, so okay I see what well the you guys are thinking of things in a different way than I am so you're thinking if I've got some stuff here How do I make these things react? That's the way you're thinking. I'm thinking generally, okay? So why why will they react if they're there? Kind of yeah, that's one kind of reason They'll hit each other. Yeah, that's kind of that temperature thing again but Okay, so and that's all right. That's all right. Okay, so in the universe I think we've talked about this that things always want to go down in energy. Okay, so since uh If you I guess if I want to say it right if I've got a Couple of things that will react together Okay, the reason that they'll react together is because the thing that they'll form is going to be at a lower overall Energy state than they are already. Okay So That's what's being shown right here. Okay, so Normally you'll see reactions spontaneous reaction specifically Where the reactants overall energy is significantly higher than the products overall energy? Okay, it's like Why does something fall down? Why doesn't it if I just put this here? Why does it just stay there? Yeah, but I mean gravity what it would that doesn't mean anything to me. Tell me more about gravity. What is happening here, huh? Okay, so it's an attractive force, right? There's an attractive force. So okay, so do I have more attraction that when I'm way up here or More attraction when I'm up here or down here. Well, it's what it what happens when it gets to the center Then that must be the last least attractive force. Is that what you're saying? If that's the least attractive force when they bounce away from each other If it's the least amount of attraction, that's like what's the most amount of attraction? It's like when they're stuck together, right? That's gonna be the most amount of attraction, right? If they're things that are not attracted to each other if they're like next to each other, what do they do? Bounce away from each other, right? Okay Yeah, so it wants to go this way, right? So it's like if I have a positive and a negative thing. What's gonna happen? They're gonna want to stick together, right? It's the same kind of thing with gravity. Although. It's not a positive negative thing Okay, so why is that? Why does it go from here to here? How about that? Let's talk about energy Yeah, how is it releasing energy? So what is this when from here to here? The difference is what? This has more What kind of energy? No, not gravity This energy, this energy, what is it called? What are the two kinds of energy? How about that? Kinetic and potential energy, okay. What are we talking about in this? Chapter, what are we talking about in this chapter? Kinetics, okay, so what is that the study of? No, we've talked about this. Okay. What's kinetics? Don't guess. What's kinetics the study of? Okay, and when we're talking Kinetics specifically is the talk topic of rates, okay, rates Okay, so Potential or kinetic energy do you think this has? So where is the kinetic energy when I'm talking about potential and kinetic energy of this system? Okay, so Okay, but so what's this got very high and this has got low what? high Potential energy why? Because it could potentially fall down, right? That's why it's got high potential energy. That's all it means, okay? Kinetics is the study of what? Rates, okay, so you could kind of think its kinetic energy is increasing as it's falling, okay? Hey, when it's doing stuff, when you're doing stuff your kinetic energy increases. Does that make sense? That should make sense to you, okay? If you don't know what the, what chapter we're talking, what we're talking about in the chapter, then it's probably going everything I'm saying is probably not registering and text messaging probably won't help you find the answer either. But anyways, okay, so what you want to always think of I'm serious. A lot of people think text messaging does help them find the answer. Anyways, what you want to think of is that the reactants are always going to be or not always in spontaneous reactions reactants are going to be at a higher energy level than products. Why, why do reactions want to occur? How about that? Let's let's ask this question again. Why do reactions want to occur? Yeah, because they want to be at a lower energy or the products are more stable than the reactants or the reactants are more what, than the products? Unstable or energetic, right? Okay, so they have more energy associated with them. Okay, so let's look at, so we're going to start writing reaction diagrams or potential energy diagrams. Okay, the same thing. Reaction diagrams, potential energy diagrams. When we have a spontaneous reaction, the reactants are going to be up here. The products are going to be down there. And we're going to lose energy. When we lose energy, do you remember I said this thing at the end has energy also? That little triangle is my little campfire symbol for energy. Okay? Okay, so what's happening in this reaction? When I say it's giving off energy, what do you think is what I'm, what am I feeling? Heat, heat, right? This is like, if you do this reaction, you can boil water, right? Because this is the reaction of the Bunsen burner. Okay, yeah, it's an exothermic reaction. Okay, so that's what we're talking about here. I don't know who, if we've talked about exothermic yet, but we can start. We call this an exothermic reaction because heat is one of the products. We can also tell that because the reactants are at a higher energy state than the products. Okay? So in order, so remember the only thing that's different between this side and this side is that they're connected to different things, right? So it's not like we're getting rid of some of these things to lower the energy, right? We're not saying, okay, now we don't have this carbon atom anymore. Okay? So how are we getting, what's happening? Where's all this energy going? Right? That's the question I just asked. That's the question I just asked and you answered it in a different way. You said that you're feeling the energy come off as heat, okay? So that's what actually happens is that the reaction will get hot, okay? In this case, it'll produce fire, you know? And keep going until you get rid of the reactants, okay? But also, when you do the Bunsen-Bernard reaction or the same reaction as like turning on a gas stove, if you guys got a gas stove at home, when I mix oxygen and methane, okay? Does just the mixture of oxygen and methane start on fire and get the reaction going? No. No, what do you have to do to it? You can't just mix those things together and then expect it to go. You have to give it a spark. You have to give it a spark. Yeah, you got to activate it. Very good. Yeah, you got to activate it, okay? So you've got to give it a bit of external energy, okay? It's like the first time you were on the diving board or something, right? And you didn't want to jump off, but your big brother was there behind you to just give you that little activation energy to get you off of that, right? Because you had a lot of potential energy and now you went down in energy. That's a spontaneous reaction as we know falling, right? Like this. This is a spontaneous reaction. Why isn't the chalk falling right now? Because I got energy. I'm giving it energy. I'm like not letting it go, okay? So once I let it go, bam, that's like the activation of it, okay? Or me pushing, you know, my little brother or whatever. I don't have a little brother, but pushing my little somebody off of the diving board. The kittens, yeah, off the diving board, okay? So here we've got So this is your reaction, your reactants, average energy. So they're just chilling like in your beaker just chilling, okay? Or they're coming out of the tube, you're smelling. It's like really smelly of rotten eggs because they just keep coming, methane and methane and methane out of there. And somebody's like, you need to like spark that thing before we all blow up, right? Then you're like, oh, that's what I haven't done, right? You know? So you get your sparker, ping, okay? You spark it. That's your activation energy, okay? So notice this, so this axis here, this y-axis is energy, okay? So we're, this is low energy. This is high energy. This is even higher energy, okay? This axis here is time or reaction progression. This is the beginning of the reaction. This will be the end of the reaction. Okay? So activation energy, we call that, and then it just goes down to products. Okay, so let's mark the activation energy. So it's from where the reactants started, all the way up to the top there. Okay, we call that the activation energy, and its symbol is EA, like that. So this is activation energy. Oh, it's just, you can think of it as like, this is how they always write it, the first letter, the first word at the bottom. But you can think of it as the energy of activation. Okay, so let's talk about an energy diagram specifically. Okay, so an energy diagram states the energy relationship for the reaction that are illustrated graphically by diagrams in which the energy of reaction is graphed on the vertical axis, like we have here, and the progress of the reaction, or over time, is on the horizontal axis. Okay, notice, also this also shows another energy, and that's this energy, from here to here. That's the difference between the reactants and the products. And remember, in this reaction, we said we're getting heat out of it. It was 211 kilojoules or something like that. That is this energy here, and we refer to that as delta H. You can think of H as heat, delta H as the change in heat. Okay, but this stands for this new term called enthalpy. Okay, so this is the enthalpy, I'll write it down. But you can think of it as the change in heat. So delta H is N, so that's just the energy difference between the reactants and products. So let's just make this a little better here, like that. Okay, so here you go, here's another common activation energy that you might be familiar with. Maybe if you guys had a jack-o'-lantern last night and lit a match to put a candle inside of it, you know, that lighting of the match is the activation energy. Of course, the match has a bunch of stored potential energy in it. How do you know that? What does it do? Yeah, it not only sparks, but like burns and it'll burn stuff, right? If you stick it on you, it'll burn you. If you throw it on like, you know, other things, it'll burn them up, right? It's got a bunch of energy in it, right? But you could keep it in a cardboard box, right? That's crazy. That is insane, right? Because like you think about matches, they like burn up cardboard like nobody's business, right? Why is that? Because we haven't given it its activation energy yet, okay? So that activation energy is what it takes to get sparked. And what do you think? The reactants on the tip of the match or the products of that reaction have more energy in them. The reactants? The reactants on the tip or the products after it's done? The reactants have much more energy. How do you know that? Oh, yeah, all of those things, right? What happens? What happens? It gives off heat, you strike it, it does that. What happens if you strike the match after it's done burned up? Nothing. Nothing will happen. Yeah, it'll break all apart, right? Okay. So in some reaction mixtures, the average total energy of the molecules is too low at the prevailing temperature for the reaction to take place at a detectable rate. This or the reaction mixture is said to be stable. For many stable mixtures, addition of a small amount of energy, just like our match, starts the reaction and continues without the addition of any more stimulus from an outside source until you use up your reactants, of course. And then the small amount of outside energy needed to spark these spontaneous things are activation energy. And then here's the match example. Okay, so you can go back to this energy diagram, the activation energy, the minimum amount of energy required to initiate the chemical reaction. You want to become familiar with the exothermic reaction, because we've gone over it quite a bit for quite a bit of a lecture today. Okay, so here's a difference in two reactions. Notice this. This guy's got a low activation energy. So this stuff is almost unstable at those conditions, okay? Right? If you put this stuff at just a little higher temperature, what would happen? It would react, right? Because what is energy and temperature like what? The same. The same, okay? So if we increase the energy here or increase the temperature, right, this stuff would react, okay? But this stuff, if we increase the temperature just a little bit, would it react? No. What about a little bit more? No, no. Because it's got a very high activation energy, okay? That makes sense, right? Okay, good. Notice here, which has the bigger delta H of these A or B, A or B. A, right? If you don't know how to do that, watch the lecture again, okay? Okay, so this reaction is known as an exothermic reaction. Why is that? It's because the reactants are at a higher energy level than the products. So the reactants have more potential energy than the products do, okay? This is also an exothermic reaction, showing, notice, the reaction mechanism at the top here, okay? The interesting thing, or not the reaction mechanism, we call this thing here the activated complex, okay? So the activated complex is an intermediate, okay? Or a transition state, I should say, a transition state. So this thing doesn't actually exist. It's the transition state between the thing forming and breaking bonds, okay? So if we were to look at our example from earlier, the transition state would be where we've got the carbon, the three hydrogens, and the bond that's about to break, really long and about to break, and the other bond that's about to form, really long and about to form, okay? This is the transition state. Notice this isn't a molecule, okay? This thing doesn't actually exist. This is like the snapshot of the boxer like hitting the other boxer, like right under the chin, mouthpiece coming out, all of that stuff. You know, this is that analogy, okay? So at the top of the, so here at the top, you'll get what we call the transition state, okay? Transition state. That's the transition from the reactants to the products. And notice you can see the kind of dashed bonds here that's partial bonds. Notice this says because it's got a large activation energy, it takes a long time for this reaction to progress, okay? Notice the transition state here. Notice the delta H. Notice the activation energy. Well, they have it as the reverse activation energy, so they're looking at it going from oxygen to, so they're saying that this is the reactants here, okay? And the last thing we want to talk about today before we get to leave is the opposite type of a reaction, where the reactants that are at a lower energy state than the products. Notice the activation energy of these reactions is very high, from way down there to way up there. Water freezing? Well, it's not really a reaction. That's a good example of an endothermic process. Well, not water freezing, water melting actually does it. It's kind of a logic little to think about, but it's pretty interesting. We'll talk about it next time, okay? So you can see the transition state of this one. Endothermic reaction, notice the high activation energy. Notice in endothermic reactions, your activation energy is going to be bigger than your delta H, okay? And exothermic reactions probably won't be. And then, yeah, you can read over essentially what we've, this is going to be like a kind of bookkeeping page. It talks about everything that we've talked about in this chapter of Tomail, okay, in terms of rates of reaction. Okay, so thanks for coming today. I'll see you guys on Wednesday, I guess. Or for those of you who are in lab, I'll see you later today. There's some, I have some more blank exam twos up here if anybody wants them, I don't know. Oh, and there should be a sign in sheet going around if you didn't sign in, make sure you do.