The discussion centers on calculating the heat supplied to 1 kmol of a multi-atomic gas heated by 100K under free expansion conditions. The correct answer is established as 3320 kJ, derived using the equation Q = ΔH = nC_pΔT, where n is the number of moles and C_p is the molar heat capacity. The participants clarify that for multi-atomic gases, the value of C_p can be approximated using x = i/2 + 1, where i represents the degrees of freedom of the gas molecules.
PREREQUISITESStudents in engineering and physics, particularly those studying thermodynamics, as well as professionals involved in heat transfer calculations and gas behavior analysis.
I do not have any definition. It is said in the task. I guess it means, there is nothing influencing the expansion of gas.Chestermiller said:What is your definition of free expansion conditions?
Usually, free expansion is defined as expansion into a vacuum. However, I don't think that is what was intended here. I think what was intended here is expansion against a constant pressure equal to the initial pressure of the gas. If that were the case, then the amount of heat supplied would be equal to the change in enthalpy of the gas. This is given by $$Q=\Delta H=nC_p\Delta T$$where n is the number of moles and ##C_p## is the molar heat capacity of the gas. Are you given no information about the gas? If not, from the answer they gave, what is the molar heat capacity of the gas?MisterP said:I do not have any definition. It is said in the task. I guess it means, there is nothing influencing the expansion of gas.
There is nothing more.. Just the temperature - 100K (how much it was risen) and 1kmole, that`s it.. Maybe the fact that it is multi-atom gas changes something?Chestermiller said:If not, from the answer they gave, what is the molar heat capacity of the gas?
Not really. What do you calculate for Cp? That might tell us something.MisterP said:There is nothing more.. Just the temperature - 100K (how much it was risen) and 1kmole, that`s it.. Maybe the fact that it is multi-atom gas changes something?
Let's see the number you get using their answer.MisterP said:I really do not know.. :(
Edit: or c = Q / (mΔT). ??
But that won`t help..
Dues the equation I wrote make sense to you? What course is this for?MisterP said:I do not get it. I have not been solving these types of tasks since I was in high school, that's around 13 years ago and now they through all the themes on basic physics and I have to solve this "easily" they say ..
We are trying to "back out" the value of Cp from the answer they gave to see if we can make any sense out of it.MisterP said:We had 3 day course on physics - starting mechanics, energy, oscilations, molecular physics, thermodynamics, electrics. I am studying electric engeneering and so, there is this fast course on physics, just for a check. I do understand Your formula, but I do not have Cp.
Very nice.MisterP said:So, I found this. E = x*n*R*T
If x = 4, then I get right answer, but I do not know if this is right. But I have seen that x is 3.
n - moles
R - 8.3 constant
T - temperature
Edit: x = i/2+1
i = 6 for multi atomic gases, so that is how to get 4 and seems like this formula works :)