Does the temperature of the gas inside a balloon changes with it expands in a vacuum chamber or does it remain constant? I've been trying to figure out if a balloon expanding in a vacuum chamber undergoes a isothermal, adiabatic or a mixture of both processes and I saw that my problem actually comes to knowing whether the temperature of the gas inside the balloon remains constant or not during the whole process.
Let's say we reach 50% of vacuum pressure inside a vacuum chamber which has a balloon inside filled with a certain gas. On the one hand, If the air inside the balloon is properly insulated from the outside, then heat transfer is negligible meaning Q = 0, which is one of the conditions for a process to be adiabatic.
Now, and here's where my confusion starts, I've read sources using this experiment to teach about Boyles law, claiming that for an ideal gas temperature should be the same and that there could be slight but negligible changes for a real gas like air, meaning the process is isothermal.
And I know that a process can be both isothermal and adiabatic, but I don't think this is the case, and crossed information confused me a lot.
Thank you in advance.
 A: If the expansion is rapid, it will be adiabatic.  If the balloon is rubber which must be stretched, the pressure will be higher inside than outside.
A: 
Now, and here's where my confusion starts, I've read sources using
this experiment to teach about Boyles law, claiming that for an ideal
gas temperature should be the same and that there could be slight but
negligible changes for a real gas like air, meaning the process is
isothermal.

The temperature of an ideal gas remains the same only if the internal energy of the gas doesn't change. If the balloon expanded adiabatically ($Q=0$) then then there will be a change (reduction) in internal energy ($\Delta U$), and thus a reduction in the temperature of the gas per the first law
$$\Delta U=Q-W$$
On the other hand, if the balloon expands isothermally (constant temperature) the expansion work done by the ideal gas needs to equal the heat transfer from the gas in the chamber to the gas in the balloon, or $Q=W$.
The question of whether it will expand isothermally or adiabatically will depend on whether or not there is an opportunity for heat to transfer between the balloon and its environment.
As @R.W. Bird pointed out, if the expansion occurs rapidly enough there may not be time for that opportunity, in which case the expansion would be adiabatic and the temperature of the gas would drop during the expansion. How rapidly it expands depends on the difference in pressure between the gas in the vacuum chamber and the gas in the balloon. The greater the difference, the more adiabatic the expansion, all other things being equal.
On the other hand, for the process to be isothermal, the expansion work done by the gas must equal the heat transfer to the gas from the air in the vacuum chamber. For that to happen, all other things being equal, the expansion would have to be slow enough for the heat transfer to keep up with the work done.  This means, as opposed to the adiabatic expansion, a small pressure difference between the gas in the balloon and the gas in the chamber would need to be maintained during the process.
Hope this helps.
