HOMEWORK POSTED IN WRONG FORUM, SO NO TEMPLATE I have encountered a problem at the university in which there is a thermally isolated container of constant volume in which the number of particles and temperature change with time(the temperature increases). The change in particle number ensures constant pressure. The question was to find the heat that is needed to change that temperature. So, naturally I would conclude from the beginning that δQ=0 since it's thermally isolated but then again, particles flow out of the system. So, I used δQ=C*dT. Our professor said that C(the heat capacity) should be that of a process of constant pressure. But, I don't quite understand why. His reasoning was that the system in reality is not in constant volume since particles flow out of it. But, my reasoning is that while particles do flow out, the remaining particles spread out in the original volume of the container and it's just the density of the gas that changes. Could someone explain to me what is the correct reasoning here? Thanks in advance!.