Texas Tech University
Temperature And Rate - Overview


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So now let's talk about the temperature effect on the reaction rates. So, first of all, what do we need for a reaction to a cure? The sink. You have this blue molecule and we have a red and yellow molecules. And let's say in the products what we want to see is blue read and yellow. Now, how we're going to have this molecule is you want this blue to collide with red to give us blue, red, yellow. But what happens if the orientation was like this? So if our blue coal is fit, Yellow Village simply give us the same result. It feel not actually a lot of collisions or cure in a normal reaction fashion. So not every collision is going to give us the reaction that we want. So one of the things that we want in our reactions to happen is collusion, orientation. What else do we want? We want, ah, lot of collisions to take place, so he wants collusion frequency. Now, after you're talking about these two, let's talk about one very important things that we deal with when reaction occurs. Let's draw and potential energy diagram, and let's say this potential energy diagram ISS for ch tree and see to become ch tree See to pull bond. And so, if you want to rotate or react ings to become our product, how does that happen? So this is our potential in Asia diagram. And over here we have C h tree and see our reactant. Over here we put a star and we call this our activated complex. And this is going to look something like this. This is C H tree and this is Hulshof Rotated. See end. And over here, our product ch three, see? And now this energy off activation is a barrier. We want our reactions to pass this barrier. Now, if you can recall firm General Kim Soo one, what we have is a graph like this. This is going to be the fraction off molecules, and this is an energy diagram, and our molecules are distributed in the on this energy. Dead grass se is distributed like this and you'll find the most energy over here. But let's say our barrier, the activation energy is over here. So Onley this part off the molecules have enough energy to get activated to reach here. If the increase the temperature, we increase the energy off the molecules. So what we're going to have is going to be something like this, mate. And as you can see, we are going to have Mawr fraction off molecules if you increase the temperature. So the third thing we need is the energy off activation off our molecules to reach the energy of activation. So now our Hennis equations is basically including all these three elements into one rate Constant K will be equal to a times. Eat the power off. Negative energy of activation over rt Over here. Car is rates constant are a is going to be frequency factor. Our energy off activation is our energy off actuacion temperature and constant. Now, if he increase t are red constant increases according to this equation, if it increase energy off activation, our que is going to decrease. And lastly, if this freaking see factor is, ah higher number, que is going to be ah, higher number. This a tends to be not changing constant with the temperature changing temperature, but you need to so keep in mind that this frequency factor is different for different kind of reactions. Okay, so Let's talk about the Chinese. Are Chinese decoration more? What we have is audience equation. K equals two a. Eat the poor off negative e a or RT. You find a natural logs off both sides. LNK would be equal to Ellen A. It's the poor off negative e a or arty. And if you can recall from your math classes Ln a Times B would be equal to Ln a plus l m B. So furthermore, what we'll have is LNK equals to Ellen. A plus. Ln eats the part off Negative e A or arty. Now again, if you can't recall from your math glasses whatever, let's say we have logarithms X base X to the power of why this means is equal to Why so in the same time, Ellen e. To the power of why would be cool to Why? Because LME's located E based hence what we're going to have is lnk equals to l. A. Minus e a over rt. Furthermore, how I can rearrange this is Ellen K equals two minus e a over our one over tea. Plus Melanie, what does it look like? So this looks like why equals two m X plus B and this will show us a, uh, graph off line. And by using this graph, we can just come up with the slope and the l N A. The, um, frequency factors natural log. And we can even, uh, come up with the Ln ky k the solution to this equation. But of course, this is not the Onley benefit we get from this equation. We can do one more thing and is going to be pretty helpful with some of the questions. So let's say you half Ln k two and that's equal to minus energy of activation or are one over t two plus Ln X Now what I mean by this KTT to is at a temperature t two. We have great constant Katie. The energy off activation doesn't change because it's the same reaction are is a constant, and the frequency factor really hardly changed with the different temperatures. So we're going to take it as it ISS. And let's try it the same thing for K one. Yeah, or are this time we're talking about the temperature at t one plus Elena. Now what we can do, we can softs tracked both sides from each other Ln k to minus lnk one equals two minus e a or are plant This is one over here t two plus Ln a minus minus e a or are part this is one over to you one plus Melanie if you call from math just as l l a Times B equals l N a plus l m B if you have Ln a minus l m b it means Ellen a over B. So if you're going to use that and this is going to become Ellen Kay tse over K one and on the right hand side, we're going to use C common parentheses E a or are pardon to see is one over t one minus one over t t. So now, with the given different temperatures and if you know one off the constance, we can't find the other. Why, sir, versa. This is going to be a very useful equation for us to be able to solve the questions that we're gonna take country. So lastly, let's talk about hey a equals two p Times e. And what they represent is P is going to be our orientation factor and our Z is coalitions frequency. So if you ever see questions that are asking us the collision frequency or orientation factor, then we can basically use the same exact, um, Formula four k equals two e to the power of negative e A or arty. And please don't forget this. A does not change with changing temperatures. So the orientation factor and the collision frequencies are going to be the exact same with the changing temperatures. And if you can recall what the orientation factor Waas. Let's say you had two molecule blue and red yellow. And if you wanted these guys to give us the molecule blue read and yellow, we need an orientation like this. If we had a collision that looks like this, then the reaction would not occur because what you want is the blue to hit the red, not dealing. And the collision frequency is basically how many collisions we have, Uh, in a period of time. So keeping these mind what we will have is going to be a that is equals two pz and we can always use the ordinance equation to be able to solve what number are collision frequency or orientation. Factors are in the given questions

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