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Reaction Rates

Pearson
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So in this video we're gonna learn about reaction rates. Now, lots of different reactions we could run to explore the rates of these reactions as a function of the concentration of the reactants. But let's start with a simple classic experiment that we call "The Simple Clock". So in the simple clock we have solution A that we're going to add to this beaker here and then we're gonna add an equal amount of solution B. And let's see how long it takes and see what happens to this reaction. So if you sit there and stare at it you may think, "Well nothing's happening". Well something is happening you just can't tell yet. If you wait long enough there's going to be a drastic change. So you see that kinda instant change to, to this blue. Now this is actually a very complicated reaction. But if we were to alter the concentrations of some of the reactants in these solutions, we would see that the time for it to turn blue would change significantly. But again it's a complicated reaction so let's just look at one component of it. And we're gonna look at iodate reacting with bisulfite. Ok so what we have here is I have four different solutions. I have a .01 M solution of iodate a .02 M solution of iodate .01 M solution of bisulfite and a .02 M solution of bisulfite. And we're going to mix them together in different orders and measure the time it takes for it to change color. Now it's not going to be this color blue, because this is complicated. But still we can get an idea of how much, how long it takes for these reactions to occur. Now, before we do that. Let's look at the rate law. So the rate law is the rate equals the rate constant times the concentration of the reactants. In this case our reactants are iodate and bisulfite. And notice I've raised them to the "x" and "y" power. We say that this is the rate law and the x and the y are the rate order. So this would be the rate order in terms of the iodate and the rate order in terms of the bisulfite. We want to determine the rate order of x and y by doing these experiments. So what we're going to do is we're gonna do these combinations of concentrations and measure the time it takes for each one of these reactions to occur. So we'll start first with the .01 M iodate and we'll measure out 50 mL of that. And then go with the, pour this in to our beaker here. And then we'll start with our .01 M solution of the bisulfite. And what I have here is a timer so as soon as I add this solution I'm going to start my timer and wait. One minute and forty seconds. So we'll write in our time up here in terms of seconds and so this took 100 seconds for that reaction. So, we'll take this one away and we'll bring out another one and this one based on our tables, we're gonna do the .02 M of the iodate. And put that one in. And then we're going to take the, again the .01 M of the bisulfite. And start our clock as soon as we add it. So that one was 51 seconds. So we'll going to our board. Write in 51 seconds. And now let's go do our next experiment. Here and so based on our table we're going to .01 M of the iodate and .02 of the bisulfite. and .02. Reset our clock. Press start as soon as we add it. So this was 53 seconds. Now what's going to happen when we do the highest concentrations for both .02 M for both the iodate and the bisulfite? You might predict in your head, what you would expect to happen. So there's the iodate. And there is the bisulfite. We'll reset our clock. And we will add this one and wait. This one was 27 seconds. So based on this data that we've just collected. What would you predict or calculate to be the reaction order for the iodate and for the bisulfate? All right, let's go calculate what that answer would be. We really don't need to really do any specific calculations. We can do most of this in our head by just noticing what happened here. So when we doubled the concentration of the iodate, notice that the time was essentially cut in half. So the reaction went twice as fast. So if we double this, we half that. That suggests, but notice that the bisulfite was held constant in both cases. .01 M, .01 M So this wasn't in play. So we double this. We half that. That means x has to be 1. It has to be a first order reaction in the iodate. Similarly, if we do the same thing with the holding the iodate fixed. Here's .01, here's .01. We go from .01 and double the bisulfite concentration. Notice that again we half it, now it's not exact but there's a lot of experimental variables we're not really controlling here. So this is pretty good. So this is being cut in half. So again, the reaction order for the bisulfite should also be 1. So the answer is going to be first order in iodate. First order in the bisulfite. And this reaction was just a check. Notice that we double both, it's going to be quartered. So it's going to be you know one-quarter the time or four times faster than the original reaction. Now let's go talk about another concept in reaction weights and thats a function of temperature, in other words if we do a reaction as a function of temperature we increase the temperature what do you expect? So here we're going to do another reaction and we're going to take the .01 M iodate and add 50 mL of that. And we're going to add it to this beaker. And we're going to heat it up. So we're going to put it there and let it heat up for a little while. Raise its temperature. And in the meantime we're going to do .01 M in the bisulfite. Have it ready to go. And while that warms up and when that get warm we're going to add this. It'll cool it down a little bit but we're gonna be warmer. What do you expect to happen to the rate of the reaction or how long it takes to react? Will it be faster, slower, or the same as at room temperature? Alright. Our solution's pretty warm let's move this out of the way, and we're gonna go add our 50 mL of the bisulfite and start our timer. And let's see how long this takes. Remember at room temperature it took a 100 seconds. So if it's going to be a faster reaction it should take less. Longer reactions should take more. 30 seconds. So you noticed that it was noticeably faster than the room temperature experiment. So heating up a reaction for the most part in general, speeds up reactions. There are exceptions to the rule but this is what you would normally see.
So in this video we're gonna learn about reaction rates. Now, lots of different reactions we could run to explore the rates of these reactions as a function of the concentration of the reactants. But let's start with a simple classic experiment that we call "The Simple Clock". So in the simple clock we have solution A that we're going to add to this beaker here and then we're gonna add an equal amount of solution B. And let's see how long it takes and see what happens to this reaction. So if you sit there and stare at it you may think, "Well nothing's happening". Well something is happening you just can't tell yet. If you wait long enough there's going to be a drastic change. So you see that kinda instant change to, to this blue. Now this is actually a very complicated reaction. But if we were to alter the concentrations of some of the reactants in these solutions, we would see that the time for it to turn blue would change significantly. But again it's a complicated reaction so let's just look at one component of it. And we're gonna look at iodate reacting with bisulfite. Ok so what we have here is I have four different solutions. I have a .01 M solution of iodate a .02 M solution of iodate .01 M solution of bisulfite and a .02 M solution of bisulfite. And we're going to mix them together in different orders and measure the time it takes for it to change color. Now it's not going to be this color blue, because this is complicated. But still we can get an idea of how much, how long it takes for these reactions to occur. Now, before we do that. Let's look at the rate law. So the rate law is the rate equals the rate constant times the concentration of the reactants. In this case our reactants are iodate and bisulfite. And notice I've raised them to the "x" and "y" power. We say that this is the rate law and the x and the y are the rate order. So this would be the rate order in terms of the iodate and the rate order in terms of the bisulfite. We want to determine the rate order of x and y by doing these experiments. So what we're going to do is we're gonna do these combinations of concentrations and measure the time it takes for each one of these reactions to occur. So we'll start first with the .01 M iodate and we'll measure out 50 mL of that. And then go with the, pour this in to our beaker here. And then we'll start with our .01 M solution of the bisulfite. And what I have here is a timer so as soon as I add this solution I'm going to start my timer and wait. One minute and forty seconds. So we'll write in our time up here in terms of seconds and so this took 100 seconds for that reaction. So, we'll take this one away and we'll bring out another one and this one based on our tables, we're gonna do the .02 M of the iodate. And put that one in. And then we're going to take the, again the .01 M of the bisulfite. And start our clock as soon as we add it. So that one was 51 seconds. So we'll going to our board. Write in 51 seconds. And now let's go do our next experiment. Here and so based on our table we're going to .01 M of the iodate and .02 of the bisulfite. and .02. Reset our clock. Press start as soon as we add it. So this was 53 seconds. Now what's going to happen when we do the highest concentrations for both .02 M for both the iodate and the bisulfite? You might predict in your head, what you would expect to happen. So there's the iodate. And there is the bisulfite. We'll reset our clock. And we will add this one and wait. This one was 27 seconds. So based on this data that we've just collected. What would you predict or calculate to be the reaction order for the iodate and for the bisulfate? All right, let's go calculate what that answer would be. We really don't need to really do any specific calculations. We can do most of this in our head by just noticing what happened here. So when we doubled the concentration of the iodate, notice that the time was essentially cut in half. So the reaction went twice as fast. So if we double this, we half that. That suggests, but notice that the bisulfite was held constant in both cases. .01 M, .01 M So this wasn't in play. So we double this. We half that. That means x has to be 1. It has to be a first order reaction in the iodate. Similarly, if we do the same thing with the holding the iodate fixed. Here's .01, here's .01. We go from .01 and double the bisulfite concentration. Notice that again we half it, now it's not exact but there's a lot of experimental variables we're not really controlling here. So this is pretty good. So this is being cut in half. So again, the reaction order for the bisulfite should also be 1. So the answer is going to be first order in iodate. First order in the bisulfite. And this reaction was just a check. Notice that we double both, it's going to be quartered. So it's going to be you know one-quarter the time or four times faster than the original reaction. Now let's go talk about another concept in reaction weights and thats a function of temperature, in other words if we do a reaction as a function of temperature we increase the temperature what do you expect? So here we're going to do another reaction and we're going to take the .01 M iodate and add 50 mL of that. And we're going to add it to this beaker. And we're going to heat it up. So we're going to put it there and let it heat up for a little while. Raise its temperature. And in the meantime we're going to do .01 M in the bisulfite. Have it ready to go. And while that warms up and when that get warm we're going to add this. It'll cool it down a little bit but we're gonna be warmer. What do you expect to happen to the rate of the reaction or how long it takes to react? Will it be faster, slower, or the same as at room temperature? Alright. Our solution's pretty warm let's move this out of the way, and we're gonna go add our 50 mL of the bisulfite and start our timer. And let's see how long this takes. Remember at room temperature it took a 100 seconds. So if it's going to be a faster reaction it should take less. Longer reactions should take more. 30 seconds. So you noticed that it was noticeably faster than the room temperature experiment. So heating up a reaction for the most part in general, speeds up reactions. There are exceptions to the rule but this is what you would normally see.