Constant-Volume Calorimetry

here, we're going to say that the heat of combustion is the amount of heat released when a mole of a substance is burned or combusted. Now recall the combustion reaction normally involves a compound with carbon and hydrogen or carbon, hydrogen and oxygen reacting with 02 Of course, there are other elements that could be involved such a sulfur or nitrogen. But the most common types of combustion reactions are just carbon and hydrogen or carbon, hydrogen and oxygen. Now we're gonna say associated with any combustion reaction is a heat of combustion value, which we represent as Delta H Not so that little circle combustion so well, abbreviate it as comb. So just remember, when discussing constant value volume telemetry, we associated with a combustion reaction.

here, it says. Which of the following statements is true about the combustion off propane? So propane a C three h eight gas. It reacts with five moles of oxygen gas to produce three moles of carbon dioxide gas, plus four moles of water vapor. It has an entropy off combustion that's equal to negative 2222 killer jewels. Here, it says. It is Endo thermic. It is exile. Thermic. It absorbs heat from the surroundings or none of the above. So remember, a combustion reaction is accompanied with a negative Delta H value, which signifies that it is an ex. A thermic process. It releases heat to the surroundings. So it is X, a thermic not in doubt, thermic. And here it's releasing heat to the surroundings. If you're absorbing heat from the surroundings, you are not eggs. A thermic you are Indo thermic. So, out of all the choices on Lee, Option B is correct.

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.

here, it says the heat capacity of a bomb calorie meter was determined by burning 12.13 g of ethane. We're told the heat of combustion equals 1000 pop 160 kg per mole and the bomb. If the temperature changed by 15.2 degrees Celsius, we have to determine the heat capacity of the bomb calorie meter. All right, so remember, that is entropy of combustion equals positive Q of object one that absorb the heat, plus Q of the calorie meter. Here we're going to convert the heat of combustion from killing jewels to Jules, which is customary with these types of questions. So remember, one killer, Jewell is 10 to the three jewels. So that is Jules per mole. Remember, Entropy of combustion is exile thermic So this is a negative sign here. Now we have 12.3 g of ethane. Ethan's formula is C And here if we converted into moles. All right, so we have two carbons, which is 24.2 g for the two carbons. And then we have six. Hydrogen is each one is 1.8 So their combined mass is 6.48 Right, So this comes from the two carbons and the six hydrogen of FAA. When we add that up together the masses 30.68 g per one mole, Take that mole. We're gonna plug it in here for the queue of the object. So the map the moles are 0.4034 moles times. It's specific heat capacity which, when you look it up, is approximately 50 to 63 Jules over moles times degree Celsius. The temperature changed by 15.2 degrees Celsius. So that's our delta. T. We're looking for the heat capacity of the calorie emitter times a change in temperature again, which is still 15 2 degrees Celsius. Moles cancel out degrees Celsius. Cancel out. When I multiply those together, I'm going to get 3 to 2. jewels, plus my heat capacity again times the change in temperature, subtract out what we have here. When we do that, we're gonna get 1559677. equals he capacity times the change in temperature divide out 15.2 degrees Celsius and when we do that, we're gonna get the heat capacity equal to 1.3 times 10 to the five jewels over degrees Celsius. Okay. So that would represent the heat capacity of the bomb calorie emitter within this given question.