All right, welcome to chemical kinetics part two. So soon enough we'll have some snow. All right, so since this is part two, you are actually familiar with this experiment. We did the exact same experiment last week, but now we're going to just look at it in a different light. Um, so we have crystal violet, which is violet or purple, which will react with sodium hydroxide and turn colorless. And we can monitor the rate of that reaction and therefore um get some kinetic information. And now instead of just um figuring out what order with respect to the reactants and the the reaction is we're actually going to use the uranous equation and figure out what the activation energy is. So hopefully you're familiar with this diagram where um you see reactants going to products and you can see because you reactants that are higher level than the products that you end up with an exothermic reaction because your um enalpy is decreasing. But you also see this big hump and we very rarely are able to actually quantify that. But that's what this lab is going to do. We're actually going to figure out exactly what our activation energy is. Okay. So, um we do that using a version of the uranous equation which has been modified a little bit mathematically. We do the natural log of both sides of that equation and then we can get a nice linear equation. Um otherwise we don't like looking at you know certainly exponential graphs. It's hard to extract data from it. But if we can linearize it, then we can end up with something that where we can easily find the activation energy from the slope of this line. Um, you also get other information from the uh, lna. And there's all kinds of very useful things out of this. But to do this, we need to plot the natural log of K versus 1 over T. So, we're going to have to measure it various temperatures. These are target temperatures. These will most likely not be your actual temperatures. In fact, they really shouldn't be. We want you to actually measure what temperatures you reach in the lab. So, it doesn't matter if you're 10°, 11°, 9°. It honestly doesn't matter. Just make sure you have four temperatures over approximately that range so that you can actually extract the data that we need. So, um you're going to measure that and then um we're going to watch the reaction occur again and then get the rate. We're going to get our K observed from our K observed, get our K and then get our ln k. So, if you haven't figured this out, you're going to want to use Excel in my opinion. So, a little review of how we found rate um from part one and found K from part one. Um we actually found the K and then the order with respect to crystal violet and the order with respect to hydroxide. So hopefully you remember what those were. Um first things first, how do we go from absorbance to concentration? Um well, we had to of course use molar absorptivity. So I want to make sure that you remember that because you're going to do that exact same thing again. And then you plotted uh concentration versus time. ln concentration versus time one over concentration versus time in order to determine which plot was linear and the answer to that question is the ln concentration versus time and once we knew that then we knew the order with respect to crystal violet was first order so if you didn't get that right last week you need to know that this week so that you can then go on and do the proper calculations from there how do you find k observed using the appropriate graph well um you want to make sure that you are using the appropriate graph get it from um the slope of that line. So because slope is equal to negative K observed as you can see in the little table down there at the bottom. Then you performed um a series of reactions with three different concentrations of hydroxide to find the order of uh of the reaction with respect to hydroxide which was again one. We use the same graphing technique that we had above and we calculated again K from K observed using this equation here where we had already measured K observed negative slope and u then we divide by the concentration of hydroxide raised to the first power because B is also one and we can get our actual K. Um and that's how we get that whole rate equation that we did last week. So this week as you might imagine since we're doing a very similar experiment with the exact same reagents a lot of the steps are actually the same. The thing that we're changing is that we are going to be doing this at four different temperatures. Um, and then when you get your K, you're going to take it, put it in a new column in Excel, and make a plot or find the natural log of that K. Um, and find our temperatures, which are measured in degrees C, convert them to Kelvin, take one over that, so we can get one over temperature and be able to plot L and K versus 1 over T. So that you can use the arraneous equation then and figure out what our activation energy is. Okay. Um, so, um, I would strongly suggest Excel because this is a great great graphing and, uh, and calculations software for that. Um, so what you're going to be doing in this particular case is we're going to be adjusting the sodium hydroxide temperature to be at our desired temperature. You're going to measure that temperature before the reaction. And then again, you're only adding one drop of crystal violet. So, we're not going to monkey with the temperature of that. We're going to collect our concentration versus time data. You're going to save that data just like you did in in um, part one last week. Um, but then you want to record the temperature after the reaction occurs. So, you're going to measure it before, then you're going to add the crystal violet. You're going to run the reaction, measure the absorption, and then record the temperature again. And then the temperature that you're going to use in your graph. Nope, I'm going to go forward. And that graph comes from the average of your before and after temperatures. Okay? So, you want to make sure you collect all that data. So, like I said, you're going to want to put this in Excel, get your four temperatures. um uh get the one over T so that you know what those temperatures are. Obviously, your temperatures are not going to be 10, 15, 25, and 30. You want to be about that, but it doesn't have to be exactly that. It want to be exactly what it is you measure. Then you're going to find your K, take your L and K, plot those, and get an equation of best fit. The tricky things uh the reason why we need to convert temperature into Kelvin is because our ideal gas constant R that we're going to need in order to use the slope to find the activation energy is in jewels per mole Kelvin. So we need to be in Kelvin. Uh the second thing you want to notice is that EA activation energy is actually in units of KJ per mole and our R value is in jewels. So be careful with that calculation and make sure that you do that conversion appropriately as well. Okay, so there's our arranous plot. Um, a couple things, um, that you want to make sure that you're doing for sure, mix, you know, put a little paraffilm over the cuette, invert it a couple times, just be consistent in exactly what you're doing before you put it in the spectr photoometer and take your measurements. The other thing you want to do, um, and hopefully you did this last week as well, is get rid of any extraneous or invalid data points. Any absorbances greater than one or less than 0.1, make sure you take those out. I think that's easier to do in Excel. We did give you instructions on how to do it in the um, in the lab software as well. Um, in any case, uh, you're going to be using ice water to get below room temperature. You're going to using a hot plate to get above room temperature. So, be careful with those. Um, but again, the exact temperature is what you're after. It doesn't matter that it's exactly 10°. It matters that you measure exactly what it actually is. Okay. Finally, um, as the temperature is changing, it's finally getting a little cooler, I want to remind you to for sure dress appropriately. Um, I was just told today one of my least favorite expressions. I always wear this. Okay, just cuz you always do it doesn't mean that you should be doing it. There are no spandex allowed. Um, please wear the appropriate shoes and dress appropriately and make sure that you are ready for lab so that you can come in and perform the lab safely. Okay, have a great