Consider an adiabatic vessel with a partition and a plug in the partition wall. On one side of the partition, there is gas at certain pressure and on the other side of partition there is perfect vacuum (at absolute zero pressure).
Now I am opening the plug. Here change in $Q$ is zero and since the gas molecules don't have to do any work to move against vacuum, change in $W$ is also zero. This means change in internal energy is zero.
Now according to whatever knowledge I have, when change in internal energy is zero, the kinetic energy of particles should remain the same. Does this mean that particles aren't moving from one partition to another? And if it isn't moving, why not. My brain is unable to comprehend the fact that particles don't move from a place at particular pressure to a place where absolute zero pressure exist. Please correct if I am wrong somewhere.
P.S. I am aware of the fact that it is physically impossible to create a zero pressure environment.