Constant-Volume Calorimetry

Jules Bruno
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here, we're going to talk about a bomb cal or emitter. Now, a bomb calorie meter is a steel container with the combustible sample submerged in a known quantity of water. And we're going to say with a bomb cal or emitter, we have the concept of constant volume kalorama tree and this is used to determine the heat released during a combustion reaction. Now here, with this whole idea, we also have constant volume itself. This just means that the calorie meter has a fixed volume that doesn't expand after the sample is combusted. So just think of a combustion reaction as kind of a controlled explosion. So there's a explosion that goes on within the bomb calorie meter itself, but the volume stays fixed, It does not expand outward. And we're going to say, since it's a combustion reaction, that would mean that it's X A thermic. This would mean that our entropy of standard combustion for this reaction would be equal to negative Q. Lost, so negative Q. The amount of heat that's lost by the reaction. Now, if we take a look here, we're gonna first look at the bomb calorie meter itself, its components. So, with the bomb calorie meter, we're gonna have a top these two wires here. These are actually the fuses that helped to ignite the combustion reaction, we're gonna say here that they go down here and inside of this orange box, this represents our combustible sample. So we'll just say that this is our sample. This reaction occurs at some designated temperature and we know that through the use of a thermometer. So here are thermometers saying It's happening at 50°C here, we're going to say that this blue outline here is actually our water and the heat that's combusted that's released by our sample. We wanna make sure that heat is evenly distributed throughout the water sample. So we use this stir and then finally itself we have our our bomb calorie emitter. So our bank will remember, the sample is combusted, gives off heat, the heat exits the bank altimeter and it goes into the water, the water there, its temperature is read by the thermometer, the heat is dissipated evenly throughout the use of the stir. Now here with the bomb calorie meter, we also have our constant volume formula here, we're going to say this is when both the liquid and calorie meter absorb heat from the hot object here, we're going to say that it's equal to negative Q lost. So the amount of heat lost equals the amount of heat gained. So, gaining heat means Q. Is positive plus the calorie meter itself. Remember up here we said that and standard of combustion is equal to negative Q. Lost. So here these are the same. So negative Q. Lost equals our standard entropy of combustion. We're going to say that this amount of heat gained is related to this portion, since the heat gain is positive, that this m cat is also positive. And then we're going to finally say that our calorie meter itself, it uses our heat capacity, which is capital C. Times the change in temperature. So we would say that this portion, when we look at it, is the constant volume formula where our standard entropy of combustion equals positive, plus our heat capacity times change in temperature.