Assume a closed and adiabatic (isolated) system (no energy or mass transfer at the boundaries) then is it possible for the average temperature to change (increase or decrease)? Corollary: 1. If yes how? Give example of a process. 2. If not. Assume a system that encloses a system that converts mass into energy (Ex. nuclear reaction). The result of the nuclear reaction is producing energy inside the closed system and decreasing the mass inside the closed system. I expect that the resulting increase of energy represents a increase in the internal energy and thus an average temperature increase. Then what is the process that offsets that to maintain the average temperature constant?
I will add an example which we were talking about. Assume a thermodynamic boundary - system - which does not exchange energy or mass with the surrounding (isolated). That closure includes a nuclear plant and the necessary energy sources to prime and sustain the nuclear reaction. All this system is isolated and has an average temperature T before initiating the reaction. The reaction is initiated - without any input of energy from outside - and a mass to energy conversion takes place. At this point the average temperature inside this system is going up, or stays the same? The argument for the temperature to go up would be that the conversion of mass to energy produces some sensitive heat which increased the average temperature of the system. But is that violating the first law - as at the boundary no energy exchange took place? If the average temperature stays the same then this heat production should be offset by something to keep the average the same. What is that?