What happens to a gas when it suddenly expands?

[bac]

My friend and i were talking about this a few days ago and he told me the process was endothermal.Is this true?If so,why?

 

[stewartcs]

My friend and i were talking about this a few days ago and he told me the process was endothermal.Is this true?If so,why?

Rapid expansions of gas are typically treated as adiabatic processes since it is assumed that there is not enough time (due to the rapid expansion) for the gas to have any heat transfer with its surroundings.

What happens to the gas really will depend on the system and how one models it.

CS